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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

Our house has a patio of stone slabs (slightly irregular size, shape and
thickness - not rectangular concrete slabs). They seem to have been laid
on bare earth, as far as I can see from looking into the gaps, without
levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've removed
the broken bits and brush away as much of the powder residue that
remains. I'm using ready-mixed mortar from B&Q, with water added to form
a stiff paste which is thick enough to adhere to a palette knife so I
can direct it into the gap (typically 5-20 mm) and then tamp it down
with my fingers (wearing rubber gloves in case the cement causes skin
irritation).

I then use the hosepipe to spray a fine mist over the sections every few
hours (given that it's hot and sunny here) so it has enough water to
cause the cement to set.

But some sections never set: even after a couple of days the mortar can
be rubbed away in a powder of sand and cement. Other sections have set
rock solid. The colour of the dry mortar varies from slate grey where
it's set to almost white (maybe with golden sand granules on top) where
it remains powdery after several days.

I've tried various alternative techniques to the stiff-paste consistency:

- adding a bit more water to the mix so it's a bit more runny, and
letting it fall off the palette knife into the gap, building up the
level gradually and then tamping it down to make it roughly level with
the slabs

- filling the section with dry ready-mix and then spraying a mist of
water over to start the setting process: repeating the misting every few
hours

I've checked that all the dry powder is thoroughly wetted, to avoid dry
sections.

No technique seems to give better or worse results. Sometimes sections
set, sometimes they dry to a firm dust that can be rubbed or washed away.

I don't know what the proportions of sand and cement are - just the
standard mortar mix.

I'm making up small batches of a few hundred grammes of dry mix, mixed
in a plastic bowl, so as not to make so much that it has started to set
before I've finished the painstaking job of tamping the mortar into the
gaps.


Should I try soaking the ground through the cracks that I'm about to
fill, to prevent the water in the mortar leaching into the ground before
it has had chance to set the mortar?


I don't need it to be a perfect job, as long as there are no longer gaps
that weeds can grow through.
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape and
thickness - not rectangular concrete slabs). They seem to have been laid
on bare earth, as far as I can see from looking into the gaps, without
levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've removed
the broken bits and brush away as much of the powder residue that
remains. I'm using ready-mixed mortar from B&Q, with water added to form
a stiff paste which is thick enough to adhere to a palette knife so I
can direct it into the gap (typically 5-20 mm) and then tamp it down
with my fingers (wearing rubber gloves in case the cement causes skin
irritation).


I forgot to say: the mortar is brand new and the bag was only opened a
few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.
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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape and
thickness - not rectangular concrete slabs). They seem to have been laid
on bare earth, as far as I can see from looking into the gaps, without
levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've removed
the broken bits and brush away as much of the powder residue that
remains. I'm using ready-mixed mortar from B&Q, with water added to form
a stiff paste which is thick enough to adhere to a palette knife so I can
direct it into the gap (typically 5-20 mm) and then tamp it down with my
fingers (wearing rubber gloves in case the cement causes skin
irritation).


I forgot to say: the mortar is brand new and the bag was only opened a few
days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.


Another thing I forgot to say. Where I've dug up the loose mortar from when
the patio was first laid (about 10 years, according to neighbours), it's
been a thin crust, in some places only about 5 mm thick, with a large void
below it down to the level of the base on which the slabs have been laid. Is
this normal? I'd have thought the whole depth of the crack between slabs
would have been filled with mortar.

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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape
and thickness - not rectangular concrete slabs). They seem to have
been laid on bare earth, as far as I can see from looking into the
gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder residue
that remains. I'm using ready-mixed mortar from B&Q, with water added
to form a stiff paste which is thick enough to adhere to a palette
knife so I can direct it into the gap (typically 5-20 mm) and then
tamp it down with my fingers (wearing rubber gloves in case the
cement causes skin irritation).


I forgot to say: the mortar is brand new and the bag was only opened a
few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.


Another thing I forgot to say. Where I've dug up the loose mortar from
when the patio was first laid (about 10 years, according to neighbours),
it's been a thin crust, in some places only about 5 mm thick, with a
large void below it down to the level of the base on which the slabs
have been laid. Is this normal? I'd have thought the whole depth of the
crack between slabs would have been filled with mortar.



When I laid my patio , about 20 years ago, I put all the pavers / slabs
on a bed of sharp sand / cement mixed at about 7 or 8:1. I have had to
re point the gaps about 3/4 times since and I use a 3:1 mix of builders
sand and cement with just enough water to make it damp and no more. .

That works of for me.

Laying the slabs on bare soil is not a good idea for a start.
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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar



"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape
and thickness - not rectangular concrete slabs). They seem to have been
laid on bare earth, as far as I can see from looking into the gaps,
without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've removed
the broken bits and brush away as much of the powder residue that
remains. I'm using ready-mixed mortar from B&Q, with water added to
form a stiff paste which is thick enough to adhere to a palette knife
so I can direct it into the gap (typically 5-20 mm) and then tamp it
down with my fingers (wearing rubber gloves in case the cement causes
skin irritation).

I forgot to say: the mortar is brand new and the bag was only opened a
few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.


Another thing I forgot to say. Where I've dug up the loose mortar from
when the patio was first laid (about 10 years, according to neighbours),
it's been a thin crust, in some places only about 5 mm thick, with a
large void below it down to the level of the base on which the slabs have
been laid. Is this normal? I'd have thought the whole depth of the crack
between slabs would have been filled with mortar.



When I laid my patio , about 20 years ago, I put all the pavers / slabs on
a bed of sharp sand / cement mixed at about 7 or 8:1. I have had to re
point the gaps about 3/4 times since and I use a 3:1 mix of builders sand
and cement with just enough water to make it damp and no more. .

That works of for me.


Not very well tho given that you have had to redo the mortar 3/4 times.

Laying the slabs on bare soil is not a good idea for a start.




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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

"RobH" wrote in message
...
When I laid my patio , about 20 years ago, I put all the pavers / slabs on
a bed of sharp sand / cement mixed at about 7 or 8:1. I have had to re
point the gaps about 3/4 times since and I use a 3:1 mix of builders sand
and cement with just enough water to make it damp and no more. .

That works of for me.


"Just enough water to make it damp and no more" sounds similar to the
consistency I've used. I found that any more runny was very difficult to
direct into the gap without it dribbling over the surface of the slabs and
having to be wiped off afterwards; it also led to patches of golden sand in
the wet mixture, rather than the grains of sand remaining coated in grey
cement.

There seems to be no rhyme or reason to which parts set like stone and which
remain the consistency of damp sand. The very first batch I made was partly
used to fill a couple of holes in the rendering on the brick wall of the
house (and that has set solid), but the rest of the same batch has set hard
in places but there are patches which haven't set -- and that's for the same
batch, all used within about 30 minutes.

I'm getting a success rate of about 1/3 ie 2/3 of what I've done will have
to be gouged out with a screwdriver and washed out so I can redo it .

How long does mortar remain workable after it has been made? I presume if it
was starting to set before I'd finished using it, it would get noticeably
more stiff and lumpy, rather than remaining a smooth paste. I'm sure I'm
getting each batch used within about 30 minutes of adding water to the dry
mix.

Is the porosity of the base that the slabs are laid on relevant? Am I right
in wondering if the "just enough water to make it damp and no more" mortar
is drying out by water leaching into the ground (or evaporating from the
surface on a hot day) before the water has had chance to react with the
cement to make it set around the sand?


The ready-mix is made by Tarmac (ie it's not B&Q's own brand of dubious
quality) and the label says "cement 15% aggregates 85%". That's a ratio of
about 5.5:1 - quite a bit less cement than the figure of between 3:1 and 4:1
that I've seen mentioned everywhere. Surprisingly the mixture ratio is not
advertised in large letters - I had to search the various paragraphs of
small print to find the 15%/85% figure.


A lot of what I see when I google "grouting/filling gaps in patio slabs"
makes it sound very easy, so there's obviously something I'm not doing
right!

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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape and
thickness - not rectangular concrete slabs). They seem to have been laid
on bare earth, as far as I can see from looking into the gaps, without
levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've removed
the broken bits and brush away as much of the powder residue that
remains. I'm using ready-mixed mortar from B&Q, with water added to form
a stiff paste which is thick enough to adhere to a palette knife so I
can direct it into the gap (typically 5-20 mm) and then tamp it down
with my fingers (wearing rubber gloves in case the cement causes skin
irritation).

I then use the hosepipe to spray a fine mist over the sections every few
hours (given that it's hot and sunny here) so it has enough water to
cause the cement to set.

But some sections never set: even after a couple of days the mortar can
be rubbed away in a powder of sand and cement. Other sections have set
rock solid. The colour of the dry mortar varies from slate grey where
it's set to almost white (maybe with golden sand granules on top) where
it remains powdery after several days.

I've tried various alternative techniques to the stiff-paste consistency:

- adding a bit more water to the mix so it's a bit more runny, and
letting it fall off the palette knife into the gap, building up the
level gradually and then tamping it down to make it roughly level with
the slabs

- filling the section with dry ready-mix and then spraying a mist of
water over to start the setting process: repeating the misting every few
hours

I've checked that all the dry powder is thoroughly wetted, to avoid dry
sections.

No technique seems to give better or worse results. Sometimes sections
set, sometimes they dry to a firm dust that can be rubbed or washed away.

I don't know what the proportions of sand and cement are - just the
standard mortar mix.

I'm making up small batches of a few hundred grammes of dry mix, mixed
in a plastic bowl, so as not to make so much that it has started to set
before I've finished the painstaking job of tamping the mortar into the
gaps.


Should I try soaking the ground through the cracks that I'm about to
fill, to prevent the water in the mortar leaching into the ground before
it has had chance to set the mortar?


I don't need it to be a perfect job, as long as there are no longer gaps
that weeds can grow through.

It's many years since I've pointed slabs but the advice used to be: to
brush-in the dry mix, brush any cement powder off the surface of the
slab and then to sprinkle a *small* amount of water on the joints and
let nature (humidity and/or light rain) take its course. By doing that
you fill the gaps, get a strong mortar and don't smudge the slabs.
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 30/05/2021 17:48, NY wrote:

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, Some of the mortar "grouting" between the slabs has cracked and
disintegrated,

Wait until it's been dry weather for a few days, then tip a good mortar
mix, dry, onto the slabs, and brush it around until it goes into the
cracks. Then go round bashing the slabs with a big lump of wood to
vibrate them, then brush some more in. Then leave it alone for a couple
of weeks, unless you're in a very dry area, in which case sprinkle a bit
of water gently all over and cover it with polythene.

Bill
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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar



"NY" wrote in message
...
"RobH" wrote in message
...
When I laid my patio , about 20 years ago, I put all the pavers / slabs
on a bed of sharp sand / cement mixed at about 7 or 8:1. I have had to
re point the gaps about 3/4 times since and I use a 3:1 mix of builders
sand and cement with just enough water to make it damp and no more. .

That works of for me.


"Just enough water to make it damp and no more" sounds similar to the
consistency I've used. I found that any more runny was very difficult to
direct into the gap without it dribbling over the surface of the slabs and
having to be wiped off afterwards; it also led to patches of golden sand
in the wet mixture, rather than the grains of sand remaining coated in
grey cement.


There seems to be no rhyme or reason to which parts set like stone and
which remain the consistency of damp sand.


But there must be.

The very first batch I made was partly used to fill a couple of holes in
the rendering on the brick wall of the house (and that has set solid),
but the rest of the same batch has set hard in places but there are
patches which haven't set -- and that's for the same batch, all used
within about 30 minutes.


Bet thats due to when you add water later after
the mixture is in the gap between the slabs, you
are washing the cement out. You arent adding
water later with the holes in the render on the
brick wall of the house.

I'm getting a success rate of about 1/3 ie 2/3 of what I've done will have
to be gouged out with a screwdriver and washed out so I can redo it .


How long does mortar remain workable after it has been made?


Quite a while.

I presume if it was starting to set before I'd finished using it, it would
get noticeably more stiff and lumpy, rather than remaining a smooth paste.
I'm sure I'm getting each batch used within about 30 minutes of adding
water to the dry mix.


Should be fine.

Is the porosity of the base that the slabs are laid on relevant?


Probably as far as the added water is concerned.

Am I right in wondering if the "just enough water to make it damp and no
more" mortar is drying out by water leaching into the ground (or
evaporating from the surface on a hot day) before the water has had chance
to react with the cement to make it set around the sand?


Probably.

The ready-mix is made by Tarmac (ie it's not B&Q's own brand of dubious
quality) and the label says "cement 15% aggregates 85%". That's a ratio of
about 5.5:1 - quite a bit less cement than the figure of between 3:1 and
4:1 that I've seen mentioned everywhere. Surprisingly the mixture ratio is
not advertised in large letters - I had to search the various paragraphs
of small print to find the 15%/85% figure.


A lot of what I see when I google "grouting/filling gaps in patio slabs"
makes it sound very easy, so there's obviously something I'm not doing
right!





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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 30/05/2021 19:41, NY wrote:
A lot of what I see when I google "grouting/filling gaps in patio slabs"
makes it sound very easy, so there's obviously something I'm not doing
right!

if you are getting non setting crumbly **** there is not enough cement

the problem with a pre iced bag is that it may after a while not have
the mixture uniform and if you use it in small quantities you may get
all cement or no cement.

It better to buy separately for small jobs and it doesn't cost a lot more



--
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and people tell those stories because everyone important believes them.
Indeed, when a conventional wisdom is at its fullest strength, ones
agreement with that conventional wisdom becomes almost a litmus test of
ones suitability to be taken seriously.€ť

Paul Krugman
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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

The Natural Philosopher wrote:
On 30/05/2021 19:41, NY wrote:
A lot of what I see when I google "grouting/filling gaps in patio slabs"
makes it sound very easy, so there's obviously something I'm not doing
right!

if you are getting non setting crumbly **** there is not enough cement

the problem with a pre iced bag is that it may after a while not have
the mixture uniform and if you use it in small quantities you may get
all cement or no cement.

It better to buy separately for small jobs and it doesn't cost a lot more

I've been doing some of this recently, I have separate cement and sand
and I've been using a 'strong' mix of maybe 2 or 3 sand to 1 cement.
I've also been using a pretty wet sort of mix which makes it easy to
get it into the gaps, they are cement slabs so a bit of splash round
the edges doesn't matter at all. The results seem pretty solid so far
(but it has only been done for a month or so).

--
Chris Green
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size,
shape and thickness - not rectangular concrete slabs). They seem to
have been laid on bare earth, as far as I can see from looking into
the gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder
residue that remains. I'm using ready-mixed mortar from B&Q, with
water added to form a stiff paste which is thick enough to adhere
to a palette knife so I can direct it into the gap (typically 5-20
mm) and then tamp it down with my fingers (wearing rubber gloves in
case the cement causes skin irritation).

I forgot to say: the mortar is brand new and the bag was only opened
a few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar
from when the patio was first laid (about 10 years, according to
neighbours), it's been a thin crust, in some places only about 5 mm
thick, with a large void below it down to the level of the base on
which the slabs have been laid. Is this normal? I'd have thought the
whole depth of the crack between slabs would have been filled with
mortar.



When I laid my patio , about 20 years ago, I put all the pavers /
slabs on a bed of sharp sandÂ* / cement mixed at about 7 or 8:1. I have
had to re point the gaps about 3/4 times since and I use a 3:1 mix of
builders sand and cement with just enough water to make it damp and no
more. .

That works of for me.


Not very well tho given that you have had to redo the mortar 3/4 times.


That was over a 20 year period tho'.
I'm not a builder so I have been learning as I go along so to speak.
Also I put it down to frost / extremely cold weather that has caused the
mortar to break up or go crumbly on the surface

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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

In article ,
RobH wrote:
On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size,
shape and thickness - not rectangular concrete slabs). They seem to
have been laid on bare earth, as far as I can see from looking into
the gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder
residue that remains. I'm using ready-mixed mortar from B&Q, with
water added to form a stiff paste which is thick enough to adhere
to a palette knife so I can direct it into the gap (typically 5-20
mm) and then tamp it down with my fingers (wearing rubber gloves in
case the cement causes skin irritation).

I forgot to say: the mortar is brand new and the bag was only opened
a few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar
from when the patio was first laid (about 10 years, according to
neighbours), it's been a thin crust, in some places only about 5 mm
thick, with a large void below it down to the level of the base on
which the slabs have been laid. Is this normal? I'd have thought the
whole depth of the crack between slabs would have been filled with
mortar.


When I laid my patio , about 20 years ago, I put all the pavers /
slabs on a bed of sharp sand / cement mixed at about 7 or 8:1. I have
had to re point the gaps about 3/4 times since and I use a 3:1 mix of
builders sand and cement with just enough water to make it damp and no
more. .

That works of for me.


Not very well tho given that you have had to redo the mortar 3/4 times.


That was over a 20 year period tho'.
I'm not a builder so I have been learning as I go along so to speak.
Also I put it down to frost / extremely cold weather that has caused the
mortar to break up or go crumbly on the surface


When we moved into this house 44 years ago, the previous owner had left a
pile to irregularly shaped paving for a path at the side of the house.
He's already laid a terrace at the back of the house. I laid the path and
40+ years later it's still looking good - no cracks between the slabs. On
the other hand, the terrace .....

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle


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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar



"RobH" wrote in message
...
On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape
and thickness - not rectangular concrete slabs). They seem to have
been laid on bare earth, as far as I can see from looking into the
gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder residue
that remains. I'm using ready-mixed mortar from B&Q, with water added
to form a stiff paste which is thick enough to adhere to a palette
knife so I can direct it into the gap (typically 5-20 mm) and then
tamp it down with my fingers (wearing rubber gloves in case the
cement causes skin irritation).

I forgot to say: the mortar is brand new and the bag was only opened a
few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar from
when the patio was first laid (about 10 years, according to
neighbours), it's been a thin crust, in some places only about 5 mm
thick, with a large void below it down to the level of the base on
which the slabs have been laid. Is this normal? I'd have thought the
whole depth of the crack between slabs would have been filled with
mortar.


When I laid my patio , about 20 years ago, I put all the pavers / slabs
on a bed of sharp sand / cement mixed at about 7 or 8:1. I have had to
re point the gaps about 3/4 times since and I use a 3:1 mix of builders
sand and cement with just enough water to make it damp and no more. .

That works of for me.


Not very well tho given that you have had to redo the mortar 3/4 times.


That was over a 20 year period tho'.


Still nothing like what it should be. You dont have to repoint
brickwork at anything even remotely like a 7 year interval.

I'm not a builder so I have been learning as I go along so to speak. Also
I put it down to frost / extremely cold weather that has caused the mortar
to break up or go crumbly on the surface


You dont get that with brickwork either.

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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 31/05/2021 09:08, Chris Green wrote:
The Natural Philosopher wrote:
On 30/05/2021 19:41, NY wrote:
A lot of what I see when I google "grouting/filling gaps in patio slabs"
makes it sound very easy, so there's obviously something I'm not doing
right!

if you are getting non setting crumbly **** there is not enough cement

the problem with a pre iced bag is that it may after a while not have
the mixture uniform and if you use it in small quantities you may get
all cement or no cement.

It better to buy separately for small jobs and it doesn't cost a lot more

I've been doing some of this recently, I have separate cement and sand
and I've been using a 'strong' mix of maybe 2 or 3 sand to 1 cement.
I've also been using a pretty wet sort of mix which makes it easy to
get it into the gaps, they are cement slabs so a bit of splash round
the edges doesn't matter at all. The results seem pretty solid so far
(but it has only been done for a month or so).


If the bag says 85% aggregates then you have bought the wrong stuff.
That sounds more like postcrete or concrete mix.

You need a bag of sand and a smaller bag of portland cement and
make up a 5:1 mix of sand:cement.
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 31/05/2021 11:01, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size,
shape and thickness - not rectangular concrete slabs). They seem
to have been laid on bare earth, as far as I can see from looking
into the gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder
residue that remains. I'm using ready-mixed mortar from B&Q, with
water added to form a stiff paste which is thick enough to adhere
to a palette knife so I can direct it into the gap (typically
5-20 mm) and then tamp it down with my fingers (wearing rubber
gloves in case the cement causes skin irritation).

I forgot to say: the mortar is brand new and the bag was only
opened a few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar
from when the patio was first laid (about 10 years, according to
neighbours), it's been a thin crust, in some places only about 5 mm
thick, with a large void below it down to the level of the base on
which the slabs have been laid. Is this normal? I'd have thought
the whole depth of the crack between slabs would have been filled
with mortar.


When I laid my patio , about 20 years ago, I put all the pavers /
slabs on a bed of sharp sandÂ* / cement mixed at about 7 or 8:1. I
have had to re point the gaps about 3/4 times since and I use a 3:1
mix of builders sand and cement with just enough water to make it
damp and no more. .

That works of for me.

Not very well tho given that you have had to redo the mortar 3/4 times.


That was over a 20 year period tho'.


Still nothing like what it should be. You dont have to repoint
brickwork at anything even remotely like a 7 year interval.

I'm not a builder so I have been learning as I go along so to speak.
Also I put it down to frost / extremely cold weather that has caused
the mortar to break up or go crumbly on the surface


You dont get that with brickwork either.


No I know that you don't get that with brickwork, but as I'm not a
builder what should I have done, ie method, mix or anything else, so it
doesn't crack, crumble or break up with cold weather.
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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

"Andrew" wrote in message
...
If the bag says 85% aggregates then you have bought the wrong stuff.
That sounds more like postcrete or concrete mix.

You need a bag of sand and a smaller bag of portland cement and
make up a 5:1 mix of sand:cement.


85% sand : 15% cement is 5.7:1 (ie 85/15 : 1)

That's not *too* far from the 5:1 that you suggest. If I need to buy any
more (depends how long the 25 kg bag of pre-mixed lasts) then I might buy
separate sand and cement and make up a slightly stronger (more cement) mix.
Is 5:1 enough? I've seen some web sites which recommend 4:1 or even 3:1.

The bag is definitely labelled "mortar". B&Q did also sell other bags
labelled "post mix".

I've done some more mortaring today, so I'll see how it sets. A patch of the
mortar that I did three days ago had dried to an almost white solid which
was actually cement/sand dust (almost like the un-wetted stuff I bought!)
even though I'd mixed it to a stiff paste just like all the other batches. I
prodded it with a screwdriver and I was left with dust - I was *almost*
tempted to mix it back to a paste with water and reuse it ;-)

I presume I want builder's sand, if I buy it separately.

Is there any significance in the colour of the "set" mortar? Dark grey
(after three days) is rock solid. Much lighter grey seems to be powder. And
that's light grey all the way through, so it's not just the surface that has
more cement to sand that what's underneath.

I'll see how it goes. It's a long slow job because the more I look the more
I find grouting that has cracked and can be pushed down into the void
between the slabs, or has turned to dust. Not sure how long ago it was
done - maybe 10 years. The cracking all occurred this more recent winter
(frost?), after looking fine before that.




When I've finished that, I need to make up wooden ramps so we can wheel a
trolley (*) up and down between three different levels of patio - and the
step height is different in each case.


(*) For bringing up loads of wood/peat/sawdust-blocks for the wood-burning
stove, and for moving loads of plant pots of bulbs onto the patio in time
for daffodils etc to flower, and then off the patio to make way for other
things in the summer.



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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

On 31 May 2021 at 14:40:04 BST, ""NY"" wrote:

"Andrew" wrote in message
...
If the bag says 85% aggregates then you have bought the wrong stuff.
That sounds more like postcrete or concrete mix.

You need a bag of sand and a smaller bag of portland cement and
make up a 5:1 mix of sand:cement.


85% sand : 15% cement is 5.7:1 (ie 85/15 : 1)

That's not *too* far from the 5:1 that you suggest. If I need to buy any
more (depends how long the 25 kg bag of pre-mixed lasts) then I might buy
separate sand and cement and make up a slightly stronger (more cement) mix.
Is 5:1 enough? I've seen some web sites which recommend 4:1 or even 3:1.

The bag is definitely labelled "mortar". B&Q did also sell other bags
labelled "post mix".

I've done some more mortaring today, so I'll see how it sets. A patch of the
mortar that I did three days ago had dried to an almost white solid which
was actually cement/sand dust (almost like the un-wetted stuff I bought!)
even though I'd mixed it to a stiff paste just like all the other batches. I
prodded it with a screwdriver and I was left with dust - I was *almost*
tempted to mix it back to a paste with water and reuse it ;-)

I presume I want builder's sand, if I buy it separately.

Is there any significance in the colour of the "set" mortar? Dark grey
(after three days) is rock solid. Much lighter grey seems to be powder. And
that's light grey all the way through, so it's not just the surface that has
more cement to sand that what's underneath.

I'll see how it goes. It's a long slow job because the more I look the more
I find grouting that has cracked and can be pushed down into the void
between the slabs, or has turned to dust. Not sure how long ago it was
done - maybe 10 years. The cracking all occurred this more recent winter
(frost?), after looking fine before that.




When I've finished that, I need to make up wooden ramps so we can wheel a
trolley (*) up and down between three different levels of patio - and the
step height is different in each case.


(*) For bringing up loads of wood/peat/sawdust-blocks for the wood-burning
stove, and for moving loads of plant pots of bulbs onto the patio in time
for daffodils etc to flower, and then off the patio to make way for other
things in the summer.


Two practical points. Firstly, the 5;1 mix is traditionally in volumes, and
bears no simple (AFAIK) relation to proportions by weight. And secondly, a
bag of mortar mix separates in store (if indeed the contents were ever mixed)
and the whole bagful needs thorough mixing in a tub or barrow before taking
some out to mix with water.

--
Roger Hayter


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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

No he needs to bite the bullet and look under one and see what was done
properly. If its on soil, depending on the composition, round here its got
a lot of clay, the soil swells and contracts, as I found at a feeble attempt
at crazy paving some years ago!
That is enough to crack any cement between stones.
As for drying but not setting, is it the narrowest slits that dry out? I
would imagine that would be the case. Cement is not very strong unless under
compression and the less there is the less the compression and the more it
turns to just powder again.
Brian

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Blind user, so no pictures please
Note this Signature is meaningless.!
"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape
and thickness - not rectangular concrete slabs). They seem to have been
laid on bare earth, as far as I can see from looking into the gaps,
without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've removed
the broken bits and brush away as much of the powder residue that
remains. I'm using ready-mixed mortar from B&Q, with water added to
form a stiff paste which is thick enough to adhere to a palette knife
so I can direct it into the gap (typically 5-20 mm) and then tamp it
down with my fingers (wearing rubber gloves in case the cement causes
skin irritation).

I forgot to say: the mortar is brand new and the bag was only opened a
few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.


Another thing I forgot to say. Where I've dug up the loose mortar from
when the patio was first laid (about 10 years, according to neighbours),
it's been a thin crust, in some places only about 5 mm thick, with a
large void below it down to the level of the base on which the slabs have
been laid. Is this normal? I'd have thought the whole depth of the crack
between slabs would have been filled with mortar.



When I laid my patio , about 20 years ago, I put all the pavers / slabs on
a bed of sharp sand / cement mixed at about 7 or 8:1. I have had to re
point the gaps about 3/4 times since and I use a 3:1 mix of builders sand
and cement with just enough water to make it damp and no more. .

That works of for me.

Laying the slabs on bare soil is not a good idea for a start.



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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape and
thickness - not rectangular concrete slabs). They seem to have been laid
on bare earth, as far as I can see from looking into the gaps, without
levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits.


Have you ruled out joint compound?

I've just laid a new patio and i'm deciding what to do as the jointing
compound is expensive, but if it outlives mortar it might be worth it.
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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar



"RobH" wrote in message
...
On 31/05/2021 11:01, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size,
shape and thickness - not rectangular concrete slabs). They seem to
have been laid on bare earth, as far as I can see from looking into
the gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder
residue that remains. I'm using ready-mixed mortar from B&Q, with
water added to form a stiff paste which is thick enough to adhere
to a palette knife so I can direct it into the gap (typically 5-20
mm) and then tamp it down with my fingers (wearing rubber gloves in
case the cement causes skin irritation).

I forgot to say: the mortar is brand new and the bag was only opened
a few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar
from when the patio was first laid (about 10 years, according to
neighbours), it's been a thin crust, in some places only about 5 mm
thick, with a large void below it down to the level of the base on
which the slabs have been laid. Is this normal? I'd have thought the
whole depth of the crack between slabs would have been filled with
mortar.


When I laid my patio , about 20 years ago, I put all the pavers /
slabs on a bed of sharp sand / cement mixed at about 7 or 8:1. I have
had to re point the gaps about 3/4 times since and I use a 3:1 mix of
builders sand and cement with just enough water to make it damp and no
more. .

That works of for me.

Not very well tho given that you have had to redo the mortar 3/4 times.

That was over a 20 year period tho'.


Still nothing like what it should be. You dont have to repoint
brickwork at anything even remotely like a 7 year interval.

I'm not a builder so I have been learning as I go along so to speak.
Also I put it down to frost / extremely cold weather that has caused the
mortar to break up or go crumbly on the surface


You dont get that with brickwork either.


No I know that you don't get that with brickwork, but as I'm not a builder
what should I have done, ie method, mix or anything else, so it doesn't
crack, crumble or break up with cold weather.


Do a better job of point the slabs, correct mix, correct
water level, correct time of year when doing it.

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Speed, the auto-contradicting senile sociopath, blabbered, again:

FLUSH the trolling senile asshole's latest troll**** unread

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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 31/05/2021 21:27, Rod Speed wrote:


"RobH" wrote in message
...
On 31/05/2021 11:01, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size,
shape and thickness - not rectangular concrete slabs). They
seem to have been laid on bare earth, as far as I can see from
looking into the gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder
residue that remains. I'm using ready-mixed mortar from B&Q,
with water added to form a stiff paste which is thick enough to
adhere to a palette knife so I can direct it into the gap
(typically 5-20 mm) and then tamp it down with my fingers
(wearing rubber gloves in case the cement causes skin irritation).

I forgot to say: the mortar is brand new and the bag was only
opened a few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar
from when the patio was first laid (about 10 years, according to
neighbours), it's been a thin crust, in some places only about 5
mm thick, with a large void below it down to the level of the
base on which the slabs have been laid. Is this normal? I'd have
thought the whole depth of the crack between slabs would have
been filled with mortar.


When I laid my patio , about 20 years ago, I put all the pavers /
slabs on a bed of sharp sandÂ* / cement mixed at about 7 or 8:1. I
have had to re point the gaps about 3/4 times since and I use a
3:1 mix of builders sand and cement with just enough water to make
it damp and no more. .

That works of for me.

Not very well tho given that you have had to redo the mortar 3/4
times.

That was over a 20 year period tho'.

Still nothing like what it should be. You dont have to repoint
brickwork at anything even remotely like a 7 year interval.

I'm not a builder so I have been learning as I go along so to speak.
Also I put it down to frost / extremely cold weather that has caused
the mortar to break up or go crumbly on the surface

You dont get that with brickwork either.


No I know that you don't get that with brickwork, but as I'm not a
builder what should I have done, ie method, mix or anything else, so
it doesn't crack, crumble or break up with cold weather.


Do a better job of point the slabs, correct mix, correct
water level, correct time of year when doing it.


Ok, so what is the correct way of pointing the slabs, if not with a trowel
What is the correct mix if not 3:1
What is the correct water level if not just enough to dampen the mix
And finally what is the correct time of year to do the job.

Thanks
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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar



"RobH" wrote in message
...
On 31/05/2021 21:27, Rod Speed wrote:


"RobH" wrote in message
...
On 31/05/2021 11:01, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size,
shape and thickness - not rectangular concrete slabs). They seem
to have been laid on bare earth, as far as I can see from looking
into the gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder
residue that remains. I'm using ready-mixed mortar from B&Q, with
water added to form a stiff paste which is thick enough to adhere
to a palette knife so I can direct it into the gap (typically
5-20 mm) and then tamp it down with my fingers (wearing rubber
gloves in case the cement causes skin irritation).

I forgot to say: the mortar is brand new and the bag was only
opened a few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar
from when the patio was first laid (about 10 years, according to
neighbours), it's been a thin crust, in some places only about 5 mm
thick, with a large void below it down to the level of the base on
which the slabs have been laid. Is this normal? I'd have thought
the whole depth of the crack between slabs would have been filled
with mortar.


When I laid my patio , about 20 years ago, I put all the pavers /
slabs on a bed of sharp sand / cement mixed at about 7 or 8:1. I
have had to re point the gaps about 3/4 times since and I use a 3:1
mix of builders sand and cement with just enough water to make it
damp and no more. .

That works of for me.

Not very well tho given that you have had to redo the mortar 3/4
times.

That was over a 20 year period tho'.

Still nothing like what it should be. You dont have to repoint
brickwork at anything even remotely like a 7 year interval.

I'm not a builder so I have been learning as I go along so to speak.
Also I put it down to frost / extremely cold weather that has caused
the mortar to break up or go crumbly on the surface

You dont get that with brickwork either.

No I know that you don't get that with brickwork, but as I'm not a
builder what should I have done, ie method, mix or anything else, so it
doesn't crack, crumble or break up with cold weather.


Do a better job of point the slabs, correct mix, correct
water level, correct time of year when doing it.


Ok, so what is the correct way of pointing the slabs, if not with a trowel
What is the correct mix if not 3:1
What is the correct water level if not just enough to dampen the mix


Thats your problem. Thats not what is done with bricklaying.

And finally what is the correct time of year to do the job.


When the cement isnt washed away.

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FLUSH the trolling senile pest's latest troll**** unread

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Rod Speed is an entirely modern phenomenon. Essentially, Rod Speed
is an insecure and worthless individual who has discovered he can
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https://www.pcreview.co.uk/threads/r...d-faq.2973853/
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 31/05/2021 23:23, Rod Speed wrote:


"RobH" wrote in message
...
On 31/05/2021 21:27, Rod Speed wrote:


"RobH" wrote in message
...
On 31/05/2021 11:01, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular
size, shape and thickness - not rectangular concrete slabs).
They seem to have been laid on bare earth, as far as I can
see from looking into the gaps, without levering up a slab to
look.

Some of the mortar "grouting" between the slabs has cracked
and disintegrated, so I'm trying to re-mortar the broken
bits. I've removed the broken bits and brush away as much of
the powder residue that remains. I'm using ready-mixed mortar
from B&Q, with water added to form a stiff paste which is
thick enough to adhere to a palette knife so I can direct it
into the gap (typically 5-20 mm) and then tamp it down with
my fingers (wearing rubber gloves in case the cement causes
skin irritation).

I forgot to say: the mortar is brand new and the bag was only
opened a few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose
mortar from when the patio was first laid (about 10 years,
according to neighbours), it's been a thin crust, in some
places only about 5 mm thick, with a large void below it down
to the level of the base on which the slabs have been laid. Is
this normal? I'd have thought the whole depth of the crack
between slabs would have been filled with mortar.


When I laid my patio , about 20 years ago, I put all the pavers
/ slabs on a bed of sharp sandÂ* / cement mixed at about 7 or
8:1. I have had to re point the gaps about 3/4 times since and I
use a 3:1 mix of builders sand and cement with just enough water
to make it damp and no more. .

That works of for me.

Not very well tho given that you have had to redo the mortar 3/4
times.

That was over a 20 year period tho'.

Still nothing like what it should be. You dont have to repoint
brickwork at anything even remotely like a 7 year interval.

I'm not a builder so I have been learning as I go along so to
speak. Also I put it down to frost / extremely cold weather that
has caused the mortar to break up or go crumbly on the surface

You dont get that with brickwork either.

No I know that you don't get that with brickwork, but as I'm not a
builder what should I have done, ie method, mix or anything else, so
it doesn't crack, crumble or break up with cold weather.

Do a better job of point the slabs, correct mix, correct
water level, correct time of year when doing it.


Ok, so what is the correct way of pointing the slabs, if not with a
trowel
What is the correct mix if not 3:1
What is the correct water level if not just enoughÂ* to dampen the mix


Thats your problem. Thats not what is done with bricklaying.

And finally what is the correct time of year to do the job.


When the cement isnt washed away.


Thanks for not answering the questions about mix and water level.

Bricklaying is a different matter as it is vertical, slab laying is
horizontal and therefore more chance of frost and ice adhering to the
mortar.

The cement is not washed away, as I did not say it was.
Never mind, if you don't know, some one else will tell me.
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 01/06/2021 07:50, RobH wrote:
The cement is not washed away, as I did not say it was.
Never mind, if you don't know, some one else will tell me.


best time is when its about half as hot as it gets, and is damp. so cool
and damp. cement will set, slowly, wont get washed away by rain, and
slabs wont expand as hot. don't want overnight frosts that will destroy
it before its sets either


--
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 01/06/2021 11:44, The Natural Philosopher wrote:
On 01/06/2021 07:50, RobH wrote:
The cement is not washed away, as I did not say it was.
Never mind, if you don't know, some one else will tell me.


best time is when its about half as hot as it gets, and is damp. so cool
and damp. cement will set, slowly, wont get washed away by rain, and
slabs wont expand as hot. don't want overnight frosts that will destroy
it before its sets either



Thanks, as I normally or have done it either spring time or maybe
September when needed.

When I have looked up what mix and how much water, all I found was
anything between 4:1 and 3:1, and just enough water so it clags or holds
in your hand. Then trowel it in the gaps, and tamping it down as I go
along. I also us a 'iron' to smooth each joint, then lightly water
afterwards, then leave it dry off
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 01/06/2021 13:48, RobH wrote:
On 01/06/2021 11:44, The Natural Philosopher wrote:
On 01/06/2021 07:50, RobH wrote:
The cement is not washed away, as I did not say it was.
Never mind, if you don't know, some one else will tell me.


best time is when its about half as hot as it gets, and is damp. so
cool and damp. cement will set, slowly, wont get washed away by rain,
and slabs wont expand as hot. don't want overnight frosts that will
destroy it before its sets either



Thanks, as I normally or have done it either spring time or maybe
September when needed.

When I have looked up what mix and how much water, all I found was
anything between 4:1 and 3:1, and just enough water so it clags or holds
in your hand. Then trowel it in the gaps, and tamping it down as I go
along. I also us a 'iron' to smooth each joint, then lightly water
afterwards, then leave it dry off

I am a fairly poor amateur bricklayer and can tell you that 5:1 is weak
crumbly and leaves spaces fir water which freezes. 2:1 is hitler bunker
grade.

It doesn't matter how much water you add - not as far as setting goes,
as anyone who has left a bag of opened cement over winter will tell you,
It absorbs all the CO2 and H2O it needs from the air...

My technique is utterly amateur. I mash it in with fingerss, a trowel -
anything and its sort of mud pie consistency

Then I remove the excess with a damp sponge RINSING EVERY STROKE

That is the key., what's left is a faint cement film and brick acid
washes that off.

--
A lie can travel halfway around the world while the truth is putting on
its shoes.
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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

It is possible that the bag had been in store for awhile and had a
small hole or other damage which has allowed the cement fines to
start to set but without turning the whole lot hard. It's possible
instore staff had noticed some harness and bashed it to break up any
fine lumps. This is never going to be any use for a decent mortar.

Also, when mixed and a proper admix used it should give a nice
'fatty' mortar. If it doesn't, don't use it. If the soil is liable
to 'heave' in cold weather, a lime-based mortar might be better but
this needs weather protection while it achieves full strngth.

Also possible that the whole batch was poorly mixed by the store
supplier and has less cement than it should.

For grouting slabs, it must be protected from frost for at least
7 days.

On 31/05/2021 16:23, Brian Gaff (Sofa) wrote:
No he needs to bite the bullet and look under one and see what was done
properly. If its on soil, depending on the composition, round here its got
a lot of clay, the soil swells and contracts, as I found at a feeble attempt
at crazy paving some years ago!
That is enough to crack any cement between stones.
As for drying but not setting, is it the narrowest slits that dry out? I
would imagine that would be the case. Cement is not very strong unless under
compression and the less there is the less the compression and the more it
turns to just powder again.
Brian


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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

On Sunday, May 30, 2021 at 5:48:14 PM UTC+1, NY wrote:
Our house has a patio of stone slabs (slightly irregular size, shape and
thickness - not rectangular concrete slabs). They seem to have been laid
on bare earth, as far as I can see from looking into the gaps, without
levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've removed
the broken bits and brush away as much of the powder residue that
remains. I'm using ready-mixed mortar from B&Q, with water added to form
a stiff paste which is thick enough to adhere to a palette knife so I
can direct it into the gap (typically 5-20 mm) and then tamp it down
with my fingers (wearing rubber gloves in case the cement causes skin
irritation).

I then use the hosepipe to spray a fine mist over the sections every few
hours (given that it's hot and sunny here) so it has enough water to
cause the cement to set.

But some sections never set: even after a couple of days the mortar can
be rubbed away in a powder of sand and cement. Other sections have set
rock solid. The colour of the dry mortar varies from slate grey where
it's set to almost white (maybe with golden sand granules on top) where
it remains powdery after several days.

I've tried various alternative techniques to the stiff-paste consistency:

- adding a bit more water to the mix so it's a bit more runny, and
letting it fall off the palette knife into the gap, building up the
level gradually and then tamping it down to make it roughly level with
the slabs

- filling the section with dry ready-mix and then spraying a mist of
water over to start the setting process: repeating the misting every few
hours

I've checked that all the dry powder is thoroughly wetted, to avoid dry
sections.

No technique seems to give better or worse results. Sometimes sections
set, sometimes they dry to a firm dust that can be rubbed or washed away.

I don't know what the proportions of sand and cement are - just the
standard mortar mix.

I'm making up small batches of a few hundred grammes of dry mix, mixed
in a plastic bowl, so as not to make so much that it has started to set
before I've finished the painstaking job of tamping the mortar into the
gaps.


Should I try soaking the ground through the cracks that I'm about to
fill, to prevent the water in the mortar leaching into the ground before
it has had chance to set the mortar?


I don't need it to be a perfect job, as long as there are no longer gaps
that weeds can grow through.


I have used this stuff just to seal up a mowing strip, it is easy peasie to use and gives a good hard wearing finish and importantly no staining.

https://www.bcprofiles.co.uk/product...kg-stone-grey/

Richard
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"RobH" wrote in message
...
On 31/05/2021 23:23, Rod Speed wrote:


"RobH" wrote in message
...
On 31/05/2021 21:27, Rod Speed wrote:


"RobH" wrote in message
...
On 31/05/2021 11:01, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:57, Rod Speed wrote:


"RobH" wrote in message
...
On 30/05/2021 18:40, NY wrote:
"NY" wrote in message
o.uk...
On 30/05/2021 17:48, NY wrote:
Our house has a patio of stone slabs (slightly irregular size,
shape and thickness - not rectangular concrete slabs). They
seem to have been laid on bare earth, as far as I can see from
looking into the gaps, without levering up a slab to look.

Some of the mortar "grouting" between the slabs has cracked and
disintegrated, so I'm trying to re-mortar the broken bits. I've
removed the broken bits and brush away as much of the powder
residue that remains. I'm using ready-mixed mortar from B&Q,
with water added to form a stiff paste which is thick enough to
adhere to a palette knife so I can direct it into the gap
(typically 5-20 mm) and then tamp it down with my fingers
(wearing rubber gloves in case the cement causes skin
irritation).

I forgot to say: the mortar is brand new and the bag was only
opened a few days ago and has been kept in a dry garage.

It's made with grey Portland cement, not white lime.

Another thing I forgot to say. Where I've dug up the loose mortar
from when the patio was first laid (about 10 years, according to
neighbours), it's been a thin crust, in some places only about 5
mm thick, with a large void below it down to the level of the
base on which the slabs have been laid. Is this normal? I'd have
thought the whole depth of the crack between slabs would have
been filled with mortar.


When I laid my patio , about 20 years ago, I put all the pavers /
slabs on a bed of sharp sand / cement mixed at about 7 or 8:1. I
have had to re point the gaps about 3/4 times since and I use a
3:1 mix of builders sand and cement with just enough water to make
it damp and no more. .

That works of for me.

Not very well tho given that you have had to redo the mortar 3/4
times.

That was over a 20 year period tho'.

Still nothing like what it should be. You dont have to repoint
brickwork at anything even remotely like a 7 year interval.

I'm not a builder so I have been learning as I go along so to speak.
Also I put it down to frost / extremely cold weather that has caused
the mortar to break up or go crumbly on the surface

You dont get that with brickwork either.

No I know that you don't get that with brickwork, but as I'm not a
builder what should I have done, ie method, mix or anything else, so
it doesn't crack, crumble or break up with cold weather.

Do a better job of point the slabs, correct mix, correct
water level, correct time of year when doing it.

Ok, so what is the correct way of pointing the slabs, if not with a
trowel
What is the correct mix if not 3:1
What is the correct water level if not just enough to dampen the mix


Thats your problem. Thats not what is done with bricklaying.

And finally what is the correct time of year to do the job.


When the cement isnt washed away.


Thanks for not answering the questions about mix


The mix is fine, I would have said if it wasnt.

and water level.


I did in fact answer that one.

Bricklaying is a different matter as it is vertical, slab laying is
horizontal and therefore more chance of frost and ice adhering to the
mortar.


Thats wrong with garden walls etc.

The cement is not washed away, as I did not say it was.


It must be if you dont get permanent grout.

Never mind, if you don't know, some one else will tell me.


I do know and did tell you.



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Default "Grouting" between existing patio slabs: how to avoid dry powdery mortar

RobH wrote
The Natural Philosopher wrote
RobH wrote


The cement is not washed away, as I did not say it was.
Never mind, if you don't know, some one else will tell me.


best time is when its about half as hot as it gets, and is damp. so cool
and damp. cement will set, slowly, wont get washed away by rain, and
slabs wont expand as hot. don't want overnight frosts that will destroy
it before its sets either


Thanks, as I normally or have done it either spring time or maybe
September when needed.


When I have looked up what mix and how much water, all I found was
anything between 4:1 and 3:1, and just enough water so it clags or holds
in your hand. Then trowel it in the gaps, and tamping it down as I go
along. I also us a 'iron' to smooth each joint, then lightly water
afterwards, then leave it dry off


You clearly arent doing it right if you have to keep redoing it so often.

Like I said, the mix is fine, so it must be the water or the time when you
do it.

Its not rocket science, others manage to get it right.

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In article , Rod Speed
wrote:
RobH wrote
The Natural Philosopher wrote
RobH wrote


The cement is not washed away, as I did not say it was. Never mind,
if you don't know, some one else will tell me.


best time is when its about half as hot as it gets, and is damp. so
cool and damp. cement will set, slowly, wont get washed away by rain,
and slabs wont expand as hot. don't want overnight frosts that will
destroy it before its sets either


Thanks, as I normally or have done it either spring time or maybe
September when needed.


When I have looked up what mix and how much water, all I found was
anything between 4:1 and 3:1, and just enough water so it clags or
holds in your hand. Then trowel it in the gaps, and tamping it down as
I go along. I also us a 'iron' to smooth each joint, then lightly
water afterwards, then leave it dry off


You clearly arent doing it right if you have to keep redoing it so often.


Like I said, the mix is fine, so it must be the water or the time when
you do it.


Its not rocket science, others manage to get it right.


Could it be that the product is not properly mixed in the bag?

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Default "Grouting" between existing patio slabs: how to avoid dry powderymortar

On 01/06/2021 20:40, charles wrote:
Could it be that the product is not properly mixed in the bag?


Of course that's the problem. But it takes 30 armchair experts to
completely confuse the OP


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