Hello,

I read this on the paving expert web site:

"There is often a temptation for installers to use either a mortar
with a higher cement content, say a 3:1 mix in place of a 6:1 mix, to
use PVA as an alleged bonding agent, or to combine a cement-rich
mortar with PVA and hope for the best. Adding cement to a mortar does
not, in very general terms, improve its adhesive properties, and PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."

It goes on to recommend using SBR. My question is, I have always
followed the instructions on the cement bag, which says to use 5:1 for
general use or 3:1 for a strong mix. The advice above, appears to
contradict that, saying a stronger mix will not actually be stronger.

To put this into context, the paragraph is talking about cementing
pavers as the treads of garden steps. I did use SBR as the web site
recommended, and they do seem rock solid but I was not using a 6:1
mix. Could I have saved cement by doing so? What ratios do you use?

Thanks,
Stephen.

On Thursday, 3 December 2015 10:27:02 UTC+1, Stephen wrote:
Hello,

I read this on the paving expert web site:

"There is often a temptation for installers to use either a mortar
with a higher cement content, say a 3:1 mix in place of a 6:1 mix, to
use PVA as an alleged bonding agent, or to combine a cement-rich
mortar with PVA and hope for the best. Adding cement to a mortar does
not, in very general terms, improve its adhesive properties, and PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."

It goes on to recommend using SBR. My question is, I have always
followed the instructions on the cement bag, which says to use 5:1 for
general use or 3:1 for a strong mix. The advice above, appears to
contradict that, saying a stronger mix will not actually be stronger.

To put this into context, the paragraph is talking about cementing
pavers as the treads of garden steps. I did use SBR as the web site
recommended, and they do seem rock solid but I was not using a 6:1
mix. Could I have saved cement by doing so? What ratios do you use?


When the instructions say "stronger mix" they mean "higher compressive
strength". They *don't* mean that the concrete sticks more firmly to
an attached brick. (Which is, at least in part, about tensile
strength).

On 03/12/15 09:27, Stephen wrote:
Hello,

I read this on the paving expert web site:

"There is often a temptation for installers to use either a mortar
with a higher cement content, say a 3:1 mix in place of a 6:1 mix, to
use PVA as an alleged bonding agent, or to combine a cement-rich
mortar with PVA and hope for the best. Adding cement to a mortar does
not, in very general terms, improve its adhesive properties, and PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."

It goes on to recommend using SBR. My question is, I have always
followed the instructions on the cement bag, which says to use 5:1 for
general use or 3:1 for a strong mix. The advice above, appears to
contradict that, saying a stronger mix will not actually be stronger.

To put this into context, the paragraph is talking about cementing
pavers as the treads of garden steps. I did use SBR as the web site
recommended, and they do seem rock solid but I was not using a 6:1
mix. Could I have saved cement by doing so? What ratios do you use?

Thanks,
Stephen.


The 2 ways I improve bonding a

1) Wet the bricks first and use a mix that in itself is right (ie not "
a bit wetter to allow for brick suckage");

2) If it's a fiddly brick - top corner for example, the ones that always
seem to fall off when "professionals" do them: Wet the brick and paint
with a cement/water slurry (honey thickness). I might switch up to a 3:1
mix too for that. My bricks do not come apart, ever... Not that's I've
done a lot - few repairs, couple of brickwork gulley drains.

SBR would work too...

On 03/12/2015 09:27, Stephen wrote:
Hello,

I read this on the paving expert web site:

"There is often a temptation for installers to use either a mortar
with a higher cement content, say a 3:1 mix in place of a 6:1 mix, to
use PVA as an alleged bonding agent, or to combine a cement-rich
mortar with PVA and hope for the best. Adding cement to a mortar does
not, in very general terms, improve its adhesive properties, and PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."

It goes on to recommend using SBR. My question is, I have always
followed the instructions on the cement bag, which says to use 5:1 for
general use or 3:1 for a strong mix. The advice above, appears to
contradict that, saying a stronger mix will not actually be stronger.

I think you are confusing a string mix (which indeed, 3:1 would be) with
one that has strong adhesion. All he is saying, is making a mix
stronger, does not make it any better at sticking slabs down.

To put this into context, the paragraph is talking about cementing
pavers as the treads of garden steps. I did use SBR as the web site
recommended, and they do seem rock solid but I was not using a 6:1
mix. Could I have saved cement by doing so? What ratios do you use?

You don't need a particularly strong mix for bedding slabs, so 6:1 would
be plenty.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 03/12/2015 18:56, John Rumm wrote:
PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."

Disagree. What PVA does (and the only thing it does) is prevent water
being sucked out of the mortar before it has had time to cure. Doesn't
matter what happens to it after that. Interesting that the end result is
the same whether you mix the PVA with the mortar or coat the surface first.

In article ,
stuart noble writes:
On 03/12/2015 18:56, John Rumm wrote:
PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."

Disagree. What PVA does (and the only thing it does) is prevent water
being sucked out of the mortar before it has had time to cure. Doesn't
matter what happens to it after that. Interesting that the end result is
the same whether you mix the PVA with the mortar or coat the surface first.

PVA/EVA/SBR all increase the tensile strength of cement based
mortars by cross linking with the set cement crystal structure.

PVA is unsuitable for use where moisture will be present, as water
dissolves PVA. EVA (usually sold as Exterior PVA although it's not
really PVA at all) is more waterproof, but *only* when used as a
mortar additive, because the cross-bonds with set cement are
insoluble. (Any excess EVA in the mix is still water soluble,
which can still cause weakness if it gets wet and there was too
much EVA or it wasn't well mixed in.) SBR goes one step further,
in that's it's not water soluble at all.

The other use for the bonding agents is where you want to bond
cement to something it doesn't stick to too well (including cement
which is already well set). Then a slurry made from cement and one
of the bonding agents at the join can work very well.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 03/12/2015 21:36, Andrew Gabriel wrote:
In article ,
stuart noble writes:
On 03/12/2015 18:56, John Rumm wrote:
PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."

Disagree. What PVA does (and the only thing it does) is prevent water
being sucked out of the mortar before it has had time to cure. Doesn't
matter what happens to it after that. Interesting that the end result is
the same whether you mix the PVA with the mortar or coat the surface first.

PVA/EVA/SBR all increase the tensile strength of cement based
mortars by cross linking with the set cement crystal structure.

PVA is unsuitable for use where moisture will be present, as water
dissolves PVA. EVA (usually sold as Exterior PVA although it's not
really PVA at all) is more waterproof, but *only* when used as a
mortar additive, because the cross-bonds with set cement are
insoluble. (Any excess EVA in the mix is still water soluble,
which can still cause weakness if it gets wet and there was too
much EVA or it wasn't well mixed in.) SBR goes one step further,
in that's it's not water soluble at all.

The other use for the bonding agents is where you want to bond
cement to something it doesn't stick to too well (including cement
which is already well set). Then a slurry made from cement and one
of the bonding agents at the join can work very well.


IME unadulterated mortar sticks well to any reasonably solid surface,
including a builder's bucket if the plastic isn't flexed. It only ever
fails when the underlying surface is porous. Never tried, but I'm sure
you could render a jam jar given the inflexibility and zero porosity.

SBR is interesting stuff but I get the impression there is no chemical
reaction with the cement, in fact you have to keep stirring it to
achieve any kind on integration.

On Friday, 4 December 2015 10:24:33 UTC, stuart noble wrote:

IME unadulterated mortar sticks well to any reasonably solid surface,
including a builder's bucket if the plastic isn't flexed. It only ever
fails when the underlying surface is porous. Never tried, but I'm sure
you could render a jam jar given the inflexibility and zero porosity.

Cement mortar does bond well to glass. But a jamjar would offer nothing to hold it up when first applied.

SBR is interesting stuff but I get the impression there is no chemical
reaction with the cement, in fact you have to keep stirring it to
achieve any kind on integration.


NT

On 04/12/15 10:24, stuart noble wrote:
Never tried, but I'm sure you could render a jam jar given the
inflexibility and zero porosity.

never seen a wall of glass bricks?


--
the biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
survival, to indulging in navel gazing and faux moral investigations
into what the world ought to be, whilst we fail utterly to deal with
what it actually is.

On Thu, 3 Dec 2015 21:36:34 -0000 (UTC),
(Andrew Gabriel) wrote:

The other use for the bonding agents is where you want to bond
cement to something it doesn't stick to too well (including cement
which is already well set). Then a slurry made from cement and one
of the bonding agents at the join can work very well.

I shall remember that for the future, thanks!

On 03/12/15 20:59, stuart noble wrote:
On 03/12/2015 18:56, John Rumm wrote:
PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."

Disagree. What PVA does (and the only thing it does) is prevent water
being sucked out of the mortar before it has had time to cure. Doesn't
matter what happens to it after that. Interesting that the end result is
the same whether you mix the PVA with the mortar or coat the surface first.

Which makes me wonder why people don't just wet the bricks - always
worked for me. I usually just have a bucket of water to dunk a few in to
form a working pile.

OK - it's not "pro" and it's not fast, but us DIY folk don;t care too
much on either front

On Thu, 3 Dec 2015 22:20:43 +0000, Tim Watts
wrote:

Which makes me wonder why people don't just wet the bricks

Why has the builder down the road covered his pile of bricks with
plastic sheeting? Can they get too wet?

On Saturday, 5 December 2015 20:51:02 UTC, Stephen wrote:
On Thu, 3 Dec 2015 22:20:43 +0000, Tim Watts
wrote:

Which makes me wonder why people don't just wet the bricks

Why has the builder down the road covered his pile of bricks with
plastic sheeting? Can they get too wet?

Yes they can, plus to protect from frost until the cement sets.

On 03/12/2015 20:59, stuart noble wrote:
On 03/12/2015 18:56, John Rumm wrote:
PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."


You are misquoting me....



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/12/2015 13:27, John Rumm wrote:
On 03/12/2015 20:59, stuart noble wrote:
On 03/12/2015 18:56, John Rumm wrote:
PVA,
being water-soluble, is a sort-term fix that will eventually be washed
away."


You are misquoting me....




Yes, sorry about that

On Thu, 03 Dec 2015 18:56:41 +0000, John Rumm
wrote:

I think you are confusing a string mix (which indeed, 3:1 would be) with
one that has strong adhesion. All he is saying, is making a mix
stronger, does not make it any better at sticking slabs down.

Thanks. I think you and Tim have solved it for me. I was interpreting
the word "strong" in a different (wrong) way.