Anyone know why they recommend sharp sand for mortar rendering onto
brickwork? I would have thought that the finer sand would stick
better...

TIA

JK

On Fri, 10 Dec 2004 15:09:57 GMT, (J Kemph)
wrote:


Anyone know why they recommend sharp sand for mortar rendering onto
brickwork? I would have thought that the finer sand would stick
better...

I'm not a bricklaying expert so if anyone knows better then they
should shout, but ...

Its not sharp versus fine, its sharp versus rounded. Spheres tend to
slide over each other whereas angular bits fit together in a less
slippery way. Well graded sand is recommended too, which means that
the grains come in a wide range of sizes, helping the sand to pack
together well.

For plastering and also I expect for bricklaying, a pure sharp sand is
not very plastic and easy to use, so a mix of sharp sand and building
sand is preferred 1:1 to 3:1 depending on the sands in question.

Anna

~~ Anna Kettle, Suffolk, England
|""""| ~ Lime plaster repairs
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk 01359 230642

"J Kemph" wrote in message
...

Anyone know why they recommend sharp sand for mortar rendering onto
brickwork? I would have thought that the finer sand would stick
better...


I **believe** it has to do with allowing moisture to escape

If you have a chemical damp-course injected, the guarantee will always
specify the use of loam free, washed sharp sand to BS 882 grade M (often
called concreting sand) for re-rendering. The grade governs the particulate
size (M = Medium). On the other hand, soft sands are generally finer with
much smaller average particulates sizes than the rather course grade M.

The reason for this is that large particles packed together result in larger
microscopic spaces between the grains, and this helps moisture escape from
previously damp walls. Using fine grained sand will fill the interstices and
slow the rate at which a damp wall can dry out.

I imagine what is good practice for known damp walls is also good practice
for walls generally. Basically it allows them to "breathe" better.

"J Kemph" wrote in message
...

Anyone know why they recommend sharp sand for mortar rendering onto
brickwork? I would have thought that the finer sand would stick
better...

You can get something called plastering sand which is between sharp and
building sand. It gives a finer finish but I'd say the sharp sticks best.

Mike typed:

"J Kemph" wrote in message
...

Anyone know why they recommend sharp sand for mortar rendering onto
brickwork? I would have thought that the finer sand would stick
better...

You can get something called plastering sand which is between sharp
and building sand

Its also more expensive, and is generally only used for the final coat which
may need to be smooth for painting etc so that it can be finished with a
float.

On Fri, 10 Dec 2004 16:27:46 GMT, "Coherers"
wrote:

"J Kemph" wrote in message
...

Anyone know why they recommend sharp sand for mortar rendering onto
brickwork? I would have thought that the finer sand would stick
better...


I **believe** it has to do with allowing moisture to escape

If you have a chemical damp-course injected, the guarantee will always
specify the use of loam free, washed sharp sand to BS 882 grade M (often
called concreting sand) for re-rendering. The grade governs the particulate
size (M = Medium). On the other hand, soft sands are generally finer with
much smaller average particulates sizes than the rather course grade M.

The reason for this is that large particles packed together result in larger
microscopic spaces between the grains, and this helps moisture escape from
previously damp walls.

Using fine grained sand will fill the interstices and
slow the rate at which a damp wall can dry out.

I imagine what is good practice for known damp walls is also good practice
for walls generally. Basically it allows them to "breathe" better.

But is this effect negated as soon as the walls are painted with
emilsion? Thanks to everyone for the explanations. -JK

"J Kemph" wrote in message
...

But is this effect negated as soon as the walls are painted with
emilsion? Thanks to everyone for the explanations. -JK

I think you are okay with emulsion as it still allows a certain amount of
moisture through. In fact now you mention it, I seem to recall the same
damp-course specs recommend the use of thin emulsion paints for just this
reason.

However, I imagine that thick oil-based paints would be a different matter.

Another reason I have heard why they use sharp sand relates to what Anna
said. The roughness of the grains gives a better key for the cement
"crystals" which form between grains, and therefore results in stronger
bonds. However, I don't think strength is the main reason because, if so,
presumably it would also be specified more widely for mortars etc.

On Sat, 11 Dec 2004 09:54:24 GMT, (J Kemph)
wrote:

But is this effect negated as soon as the walls are painted with
emilsion? Thanks to everyone for the explanations. -JK

Yes and that is one reason to eschew (good word huh?!) emulsion paint
in favour of limewash, which contrary to bad press does not rub off in
clothing if it is put on properly

And the other reason is that any business that can afford adverts on
primetime TV is making too much money. Limewash is cheap

Anna

~~ Anna Kettle, Suffolk, England
|""""| ~ Lime plaster repairs
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk 01359 230642

"Anna Kettle" wrote in message
...
On Sat, 11 Dec 2004 09:54:24 GMT, (J Kemph)
wrote:

But is this effect negated as soon as the walls are painted with
emilsion? Thanks to everyone for the explanations. -JK

Yes and that is one reason to eschew (good word huh?!)

Great word. I use it as often as I can, never eschew the opportunity.

Limewash is cheap

But it makes you have babies :-(

Mary

On Sat, 11 Dec 2004 17:43:52 -0000, "Mary Fisher"
wrote:

Limewash is cheap

But it makes you have babies :-(

Puzzled Limewash, the noted aphrodisiac /Puzzled

Oh - and a third reason to use it. It is very fashionable according to
some clients of mine who are in marketing and up on such things

Anna

~~ Anna Kettle, Suffolk, England
|""""| ~ Lime plaster repairs
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk 01359 230642

"Anna Kettle" wrote in message
...
On Sat, 11 Dec 2004 17:43:52 -0000, "Mary Fisher"
wrote:

Limewash is cheap

But it makes you have babies :-(

Puzzled Limewash, the noted aphrodisiac /Puzzled

LOL! My mother's generation always felt the need to whitewash the outside
privvy or cellar just before they went into labour. I always thought it was
an old wives' tale but guess what I had an urge to do before I was carted
off to the labour ward?

Oh - and a third reason to use it. It is very fashionable according to
some clients of mine who are in marketing and up on such things

Oh well, I'll do it if only for that and risk the babies ... :-)

Mary

"Mary Fisher" wrote in message
et...

"Anna Kettle" wrote in message
...
On Sat, 11 Dec 2004 09:54:24 GMT, (J Kemph)
wrote:

But is this effect negated as soon as the walls are painted with
emilsion? Thanks to everyone for the explanations. -JK

Yes and that is one reason to eschew (good word huh?!)

Great word. I use it as often as I can, never eschew the opportunity.

Limewash is cheap

But it makes you have babies :-(


Welll I've heard many good things assigned to the use of lime, many true,
but never that one.

"Andrew Gabriel" wrote in message
...

Mortars aren't supposed to be strong. They are supposed to break
in preference to the bricks breaking, in the even of any movement.

--
That is what my builder said when I caught him using 10:1 ;-)

"Andrew Gabriel" wrote in message
...

Mortars aren't supposed to be strong. They are supposed to break
in preference to the bricks breaking, in the even of any movement.

That reminds me of a question which has never had a 100% satisfactory
answer:

What is mortar for?

a) to hold bricks together?

b) to hold bricks apart?

Mary

--
Andrew Gabriel

In article , "Mary
Fisher" says...

"Andrew Gabriel" wrote in message
...

Mortars aren't supposed to be strong. They are supposed to break
in preference to the bricks breaking, in the even of any movement.

That reminds me of a question which has never had a 100% satisfactory
answer:

What is mortar for?

a) to hold bricks together?

b) to hold bricks apart?

Yes.

"Rob Morley" wrote in message
t...
In article , "Mary
Fisher" says...

"Andrew Gabriel" wrote in message
...

Mortars aren't supposed to be strong. They are supposed to break
in preference to the bricks breaking, in the even of any movement.

That reminds me of a question which has never had a 100% satisfactory
answer:

What is mortar for?

a) to hold bricks together?

b) to hold bricks apart?

Yes.

I forgot the 'or' between a and b. Silly me :-)

Mary

In article ,
"Mary Fisher" writes:

"Andrew Gabriel" wrote in message
...

Mortars aren't supposed to be strong. They are supposed to break
in preference to the bricks breaking, in the even of any movement.

That reminds me of a question which has never had a 100% satisfactory
answer:

What is mortar for?

a) to hold bricks together?

No, that's what gravity is for.

b) to hold bricks apart?

Not really.
The purpose is to prevent (or at least to limit) the realative
movement between adjacent bricks. In theory, you could build the
same building with no mortar, but it would be fragile (think of
a dry stone wall or a pile of childrens building blocks).

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
"Mary Fisher" writes:

"Andrew Gabriel" wrote in message
...

Mortars aren't supposed to be strong. They are supposed to break
in preference to the bricks breaking, in the even of any movement.

That reminds me of a question which has never had a 100% satisfactory
answer:

What is mortar for?

a) to hold bricks together?

No, that's what gravity is for.

b) to hold bricks apart?

Not really.
The purpose is to prevent (or at least to limit) the realative
movement between adjacent bricks. In theory, you could build the
same building with no mortar, but it would be fragile (think of
a dry stone wall or a pile of childrens building blocks).

You think a dry stone wall is fragile???

But it's a good answer - in relation to bricks. Thanks.

Mary

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
"Mary Fisher" writes:

"Andrew Gabriel" wrote in message
...

Mortars aren't supposed to be strong. They are supposed to break
in preference to the bricks breaking, in the even of any movement.

That reminds me of a question which has never had a 100% satisfactory
answer:

What is mortar for?

a) to hold bricks together?

No, that's what gravity is for.

b) to hold bricks apart?

Not really.
The purpose is to prevent (or at least to limit) the realative
movement between adjacent bricks. In theory, you could build the
same building with no mortar, but it would be fragile (think of
a dry stone wall or a pile of childrens building blocks).

Although true in a brick house, in a random stone house the stones lain on
top of each other are quite stable - 24 inches of thickness sees to that -
and I'd say the mortar, which is only on the inner and outer 4 inches or so
is to stop the weather getting into the wall (outer) and to provide a
sensible surface (inner).

"Mike" wrote in message
...

"Andrew Gabriel" wrote in message
...
In article ,
"Mary Fisher" writes:


What is mortar for?

a) to hold bricks together?

No, that's what gravity is for.

b) to hold bricks apart?

Not really.
The purpose is to prevent (or at least to limit) the realative
movement between adjacent bricks. In theory, you could build the
same building with no mortar, but it would be fragile (think of
a dry stone wall or a pile of childrens building blocks).

Although true in a brick house, in a random stone house the stones lain on
top of each other are quite stable - 24 inches of thickness sees to that -
and I'd say the mortar, which is only on the inner and outer 4 inches or
so
is to stop the weather getting into the wall (outer) and to provide a
sensible surface (inner).

That's another good reply.

I wish I'd had you lot around when my dad used to tease me with this!

Mary

"Mary Fisher" wrote in message
et...
The purpose is to prevent (or at least to limit) the realative
movement between adjacent bricks. In theory, you could build the
same building with no mortar, but it would be fragile (think of
a dry stone wall or a pile of childrens building blocks).

You think a dry stone wall is fragile???

It is while you are building it. I know of cases of people round here being
killed doing so.

Also they are when ******* ramblers stand on them for a better look when
then climb over the stile meant for this purpose.

There is still one good use for foxhounds.

The message
from "Mike" contains these words:

You think a dry stone wall is fragile???

It is while you are building it. I know of cases of people round here being
killed doing so.

Not in my experience. I confidently stand on incomplete walls when I
build them.

Also they are when ******* ramblers stand on them for a better look when
then climb over the stile meant for this purpose.

200 year old walls where the cowboys who built them didn't as much as
strip the turf off the ground before throwing them up are a prime
candidates for collapse but a well built wall on subsoil that has not
been abused has as much chance of lasting as a mortared wall.

--
Roger

"Mike" wrote in message
...

You think a dry stone wall is fragile???

It is while you are building it. I know of cases of people round here
being
killed doing so.

I don't. so what does that prove?

People are killed on building sites of all kinds.

Also they are when ******* ramblers stand on them for a better look when
then climb over the stile meant for this purpose.

Anything can be dangerous if misused.

Mary

Mortar is used to spread the stresses between bricks evenly; you could use
dry sand were it not likely to dribble away. No masonry structure relying
the tensional strength of mortar will stay up for long. I have seen a Roman
aquaduct in Spain constructed of stone only, no mortar. Friction and its own
weight keeps it together. In order to forestall problems with uneven
stresses causing cracking though, they had to shape the individual stones to
fit each other quite accurately.

Of course with bricks, since they are relatively light, a little bit of
tensional strength in the mortar does no harm, especially on the lightly
loaded upper parts of walls.

Andy.

"Roger" wrote in message
k...
The message
from "Mike" contains these words:

You think a dry stone wall is fragile???

It is while you are building it. I know of cases of people round here
being
killed doing so.

Not in my experience. I confidently stand on incomplete walls when I
build them.

All I can say then is "Are you near the Peak District and are you looking
for work."

"Roger" wrote in message
k...

Also they are when ******* ramblers stand on them for a better look when
then climb over the stile meant for this purpose.

200 year old walls where the cowboys who built them didn't as much as
strip the turf off the ground before throwing them up are a prime
candidates for collapse but a well built wall on subsoil that has not
been abused has as much chance of lasting as a mortared wall.

Quite possibly. But the fact is most dry stone walls are on dodgy footings
and any abuse causes them to fail.

"Mike" wrote in message
...

"Roger" wrote in message
k...

Also they are when ******* ramblers stand on them for a better look
when
then climb over the stile meant for this purpose.

200 year old walls where the cowboys who built them didn't as much as
strip the turf off the ground before throwing them up are a prime
candidates for collapse but a well built wall on subsoil that has not
been abused has as much chance of lasting as a mortared wall.

Quite possibly. But the fact is most dry stone walls are on dodgy
footings
and any abuse causes them to fail.

Evidence?

(not anecdote, opinion or personal experience)

"Mary Fisher" wrote in message
et...

"Mike" wrote in message
...

"Roger" wrote in message
k...

Also they are when ******* ramblers stand on them for a better look
when
then climb over the stile meant for this purpose.

200 year old walls where the cowboys who built them didn't as much as
strip the turf off the ground before throwing them up are a prime
candidates for collapse but a well built wall on subsoil that has not
been abused has as much chance of lasting as a mortared wall.

Quite possibly. But the fact is most dry stone walls are on dodgy
footings
and any abuse causes them to fail.

Evidence?

(not anecdote, opinion or personal experience)

What sort of evidence will you accept then ?

I personally own several miles of dry stone wall and both cattle and
ramblers damage it regularly. As soon as they're damaged in the slightest
way they seem to deteriorate into a pile of stones amazing rapidly.

"Mike" wrote in message
...

"Mary Fisher" wrote in message
et...

"Mike" wrote in message
...

"Roger" wrote in message
k...

Also they are when ******* ramblers stand on them for a better look
when
then climb over the stile meant for this purpose.

200 year old walls where the cowboys who built them didn't as much as
strip the turf off the ground before throwing them up are a prime
candidates for collapse but a well built wall on subsoil that has not
been abused has as much chance of lasting as a mortared wall.

Quite possibly. But the fact is most dry stone walls are on dodgy
footings
and any abuse causes them to fail.

Evidence?

(not anecdote, opinion or personal experience)

What sort of evidence will you accept then ?

I personally own several miles of dry stone wall and both cattle and
ramblers damage it regularly. As soon as they're damaged in the slightest
way they seem to deteriorate into a pile of stones amazing rapidly.

Perhaps they weren't well built in the first plce or not well maintained ...

But you said copy and paste " ... most dry stone walls ... "

Your own experience is not valid in this context.

Mary

Mary

In article , "andrewpreece"
says...
Mortar is used to spread the stresses between bricks evenly; you could use
dry sand were it not likely to dribble away. No masonry structure relying
the tensional strength of mortar will stay up for long. I have seen a Roman
aquaduct in Spain constructed of stone only, no mortar. Friction and its own
weight keeps it together. In order to forestall problems with uneven
stresses causing cracking though, they had to shape the individual stones to
fit each other quite accurately.

Of course with bricks, since they are relatively light, a little bit of
tensional strength in the mortar does no harm, especially on the lightly
loaded upper parts of walls.

tensile :-)

"Mary Fisher" wrote in message
et...

"Mike" wrote in message
...

"Mary Fisher" wrote in message
et...

"Mike" wrote in message
...

"Roger" wrote in message
k...

Also they are when ******* ramblers stand on them for a better
look
when
then climb over the stile meant for this purpose.

200 year old walls where the cowboys who built them didn't as much
as
strip the turf off the ground before throwing them up are a prime
candidates for collapse but a well built wall on subsoil that has
not
been abused has as much chance of lasting as a mortared wall.

Quite possibly. But the fact is most dry stone walls are on dodgy
footings
and any abuse causes them to fail.

Evidence?

(not anecdote, opinion or personal experience)

What sort of evidence will you accept then ?

I personally own several miles of dry stone wall and both cattle and
ramblers damage it regularly. As soon as they're damaged in the
slightest
way they seem to deteriorate into a pile of stones amazing rapidly.

Perhaps they weren't well built in the first plce or not well maintained
....

But you said copy and paste " ... most dry stone walls ... "

Your own experience is not valid in this context.

Would you accept a comment from the Peak District farmer's association then
? That would cover possibly 20% of dry stone walling the country and a far
higher percentage of ramblers.

The message
from "andrewpreece" contains these words:

Mortar is used to spread the stresses between bricks evenly; you could use
dry sand were it not likely to dribble away. No masonry structure relying
the tensional strength of mortar will stay up for long. I have seen a Roman
aquaduct in Spain constructed of stone only, no mortar. Friction and its own
weight keeps it together. In order to forestall problems with uneven
stresses causing cracking though, they had to shape the individual stones to
fit each other quite accurately.

Lime mortar can wash out of the joints on exposed walls (the outer skin
of the gable end of my barn has an area of about 10 feet square with
almost none in sight) but the Romans were dab hands at making a cement
mortar that could last 2000 years even exposed to the elements.

--
Roger

"Mike" wrote in message
...

"Mary Fisher" wrote in message
et...

"Mike" wrote in message
...

"Mary Fisher" wrote in message
et...

"Mike" wrote in message
...

"Roger" wrote in message
k...

Also they are when ******* ramblers stand on them for a better
look
when
then climb over the stile meant for this purpose.

200 year old walls where the cowboys who built them didn't as much
as
strip the turf off the ground before throwing them up are a prime
candidates for collapse but a well built wall on subsoil that has
not
been abused has as much chance of lasting as a mortared wall.

Quite possibly. But the fact is most dry stone walls are on dodgy
footings
and any abuse causes them to fail.

Evidence?

(not anecdote, opinion or personal experience)

What sort of evidence will you accept then ?

I personally own several miles of dry stone wall and both cattle and
ramblers damage it regularly. As soon as they're damaged in the
slightest
way they seem to deteriorate into a pile of stones amazing rapidly.

Perhaps they weren't well built in the first plce or not well maintained
...

But you said copy and paste " ... most dry stone walls ... "

Your own experience is not valid in this context.

Would you accept a comment from the Peak District farmer's association
then
? That would cover possibly 20% of dry stone walling the country and a
far
higher percentage of ramblers.

LOL! It might also say more about the maintenance in the Peak District than
anything else :-)

Mary

"Mary Fisher" wrote in message
et...
But you said copy and paste " ... most dry stone walls ... "

Your own experience is not valid in this context.

Would you accept a comment from the Peak District farmer's association
then
? That would cover possibly 20% of dry stone walling the country and a
far
higher percentage of ramblers.

LOL! It might also say more about the maintenance in the Peak District
than
anything else :-)


I think what it shows is there is a distinct shortage of dry stone wallers
to undertake maintainence and repair work, hence my offer of work to the
other poster. I doubt if the situation is any better elsewhere though I
accept I don't visit those areas and cannot judge.

"Mike" wrote in message
...

"Mary Fisher" wrote in message
et...
But you said copy and paste " ... most dry stone walls ... "

Your own experience is not valid in this context.

Would you accept a comment from the Peak District farmer's association
then
? That would cover possibly 20% of dry stone walling the country and a
far
higher percentage of ramblers.

LOL! It might also say more about the maintenance in the Peak District
than
anything else :-)


I think what it shows is there is a distinct shortage of dry stone wallers
to undertake maintainence and repair work,

Indeed. Not the integrity of a wellbuilt stone wall.

hence my offer of work to the
other poster. I doubt if the situation is any better elsewhere though I
accept I don't visit those areas and cannot judge.

Quite. That's the danger of words like "most".

We all do it ... :-(

Mary

On Tue, 14 Dec 2004 13:31:33 GMT, Roger
wrote:

Lime mortar can wash out of the joints on exposed walls

Not once it is set it can't. What you are seeing is the results of
sacrificial weathering which is a GOOD THING and you should be
inspired to repoint your gable end come springtime

The Romans were dab hands at making a cement
mortar that could last 2000 years even exposed to the elements.

Roman cement is not cement as we know it today. Today's cement is
produced at much higher temperatures and is much harder and stronger
than Roman cement. If you want the Roman cement effect today then
either use a feebly hydraulic lime mortar (NHL 3.5) or use a lime
putty mortar with 20% of the aggregate being a pozzolan. The Romans
used volcanic ash as a pozzolan, but brick dust is more readily
avaiable in England

Anna

~~ Anna Kettle, Suffolk, England
|""""| ~ Lime plaster repairs
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk 01359 230642

The message
from (Anna Kettle) contains these words:

Lime mortar can wash out of the joints on exposed walls

Not once it is set it can't. What you are seeing is the results of
sacrificial weathering which is a GOOD THING and you should be
inspired to repoint your gable end come springtime

I am more inclined to tear down the outer skin of that section of the
gable end and rebuild. It will probably be quicker than squeezing
bucketfuls of mortar into the gaping holes that smile at me as I pass
and being stone it should all be reusable. However any action on that
wall is some way down the pile of tuits (round).

The Romans were dab hands at making a cement
mortar that could last 2000 years even exposed to the elements.

Roman cement is not cement as we know it today. Today's cement is
produced at much higher temperatures and is much harder and stronger
than Roman cement. If you want the Roman cement effect today then
either use a feebly hydraulic lime mortar (NHL 3.5) or use a lime
putty mortar with 20% of the aggregate being a pozzolan. The Romans
used volcanic ash as a pozzolan, but brick dust is more readily
avaiable in England

Brick? What's that?

I haven't been close to original Roman walling lately to test how hard
it is but I don't rate cement mortar as hard (except when compared with
lime mortar). There are a good many examples of Roman masonry that have
survived 2000 years. That bit of my gable end has lost its mortar in 400
or possibly much less).

--
Roger

"Roger" wrote in message
k...
The message
from (Anna Kettle) contains these words:

Lime mortar can wash out of the joints on exposed walls

Not once it is set it can't. What you are seeing is the results of
sacrificial weathering which is a GOOD THING and you should be
inspired to repoint your gable end come springtime

I am more inclined to tear down the outer skin of that section of the
gable end and rebuild. It will probably be quicker than squeezing
bucketfuls of mortar into the gaping holes that smile at me as I pass
and being stone it should all be reusable. However any action on that
wall is some way down the pile of tuits (round).

Consider finding and hiring one of those render sprayers they used for
spraying lime render in a recent Grand Designs.



I haven't been close to original Roman walling lately to test how hard
it is but I don't rate cement mortar as hard (except when compared with
lime mortar). There are a good many examples of Roman masonry that have
survived 2000 years. That bit of my gable end has lost its mortar in 400
or possibly much less).

That's not bad going really, is it. The average Barrett hutch will have
crumbled to dust in half this time. Or even less hopefully.


--
Roger

"Roger" wrote in message
k...
The message
from (Anna Kettle) contains these words:

Lime mortar can wash out of the joints on exposed walls

Not once it is set it can't. What you are seeing is the results of
sacrificial weathering which is a GOOD THING and you should be
inspired to repoint your gable end come springtime

I am more inclined to tear down the outer skin of that section of the
gable end and rebuild. It will probably be quicker than squeezing
bucketfuls of mortar into the gaping holes that smile at me as I pass
and being stone it should all be reusable. However any action on that
wall is some way down the pile of tuits (round).

The Romans were dab hands at making a cement
mortar that could last 2000 years even exposed to the elements.

Roman cement is not cement as we know it today. Today's cement is
produced at much higher temperatures and is much harder and stronger
than Roman cement. If you want the Roman cement effect today then
either use a feebly hydraulic lime mortar (NHL 3.5) or use a lime
putty mortar with 20% of the aggregate being a pozzolan. The Romans
used volcanic ash as a pozzolan, but brick dust is more readily
avaiable in England


Fly ash from a power station is an excellant Pozzolan. Certain stations
produce better grade than others and if the situation of ten years ago
hasn't changed Eggborough in yorkshire, Fiddlers Ferry near Warrington,
Ironbridge, and Rugely are (were) more consistent than others

I haven't been close to original Roman walling lately to test how hard
it is

It is hard. You are right it is not going anywhere in a hurry

I don't rate cement mortar as hard (except when compared with
lime mortar)

You would if a lump landed on your head

There are a good many examples of Roman masonry that have
survived 2000 years. That bit of my gable end has lost its mortar in 400
or possibly much less).

Maybe that is something to do with what materials were available at
the time.

400 years Queen Elizabeth I was about to die and I don't think the
road transport system was any great shakes so whoever built your gable
end used lime dug out of the ground half a mile away and local sand
which might not have the right amount of clay in it and the particles
might be poorly graded

Contrariwise, whoever built the Roman buildings had an efficient
supply system (Roman roads and slaves) to bring materials from further
away

Anna
~~ Anna Kettle, Suffolk, England
|""""| ~ Lime plaster repairs
/ ^^ \ // Freehand modelling in lime: overmantels, pargeting etc
|____| www.kettlenet.co.uk 01359 230642