PVA in cement

[Guy King]

I saw someone putting a dollop of PVA into some cement he was mixing.

What's that do then?

 

[Guy King]

The message <[email protected]>

It makes the mortar tougher. It can also increase adhesion. It's also
almost always not needed, often not desirable.

What would make it undesirable?

 

[The Natural Philosopher]

I saw someone putting a dollop of PVA into some cement he was mixing.

What's that do then?

What it does is make the grains of sand slide over each other a little,
this 'plasticising' the mix, and also , if its a fairly weak (low
cement) mix fills up the gaps between the grains and stops water soaking
in quite as much.

I.e. reduces porosity and 'waterproofs' the mix.

 

[The3rd Earl Of Derby]

I saw someone putting a dollop of PVA into some cement he was mixing.

What's that do then?

In reality it serves no purpose whatsover.

Most victorian properties have been up a hundred years,there was no PVA
then.

/awaits the antagonist.

 

[Grunff]

What would make it undesirable?

IME nothing - PVA is a great additive, it plasticises, and improves
adhesion significantly. If you add enough of it, you end up with a
relatively non-porous finish.

 

[Steve Walker]

IME nothing - PVA is a great additive, it plasticises, and
improves adhesion significantly. If you add enough of it, you end
up with a relatively non-porous finish.

I agree - I lob it in every mix.

 

[Weatherlawyer]

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What would make it undesirable?

It would become a PITA to remove from the facework even with brick
acid. It is used in self leveler. If you are using it in a grout it
will stop it spalling or failing through drying too quickly.

You can use it in small mixes that you make just for patching. It's a
waste of time and money in large jobs.

 

[Andrew Gabriel]

IME nothing - PVA is a great additive, it plasticises, and improves
adhesion significantly. If you add enough of it, you end up with a
relatively non-porous finish.

Actually, you can only use a relatively small amount of PVA
in mortar which is going to be exposed to moisture, or it
will cause the PVA/mortar to eventually fail. You only need
a small amount anyway -- something like a teaspoon per shovel
load of cement to get maximum effect. If you need any more
than this in circumstances where the mortar is going to be
exposed to moisture e.g. to make up some sort of bonding mix,
then you must use EVA (which is sold as waterproof PVA,
although it's not strictly PVA). SBR is another alternative
suitable for moist conditions (Lafarge's helpline suggested
it to me on one occasion), but not having tried it myself,
I don't know which of PVA's various properties it imparts to
the mortar.