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Tiling newly bonded/ plastered walls

Postby andypty » Tue Mar 15, 2011 1:14 pm

I have recently bought an old house (1840s) and the old plaster in the bathroom was loose so has been removed/ fell off!!
I have had the wall re-rendered/bonded (with a lime-based product due to the general slightly damp conditions) and now want to tile the walls for a bathroom.

I have looked through the forums and there seems to be a lot of 'debate' as to whether to PVA the walls or not before tiling them.

Therefore any advice on whether I should PVA the walls or use an alternative product before tiling them would be greatly apprecaited.

I have bought a decent tile adhesive to use on the travertine tiles I plan on using, and then will seal them after to aim to prevent any water leaking (hopefully!?!).

Thanks for any help or advice.

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Postby chris_on_tour2002 » Tue Mar 15, 2011 8:22 pm

well all that your post is going to achieve is to re-ignite the eternal question!! the debate isn't going to go away because you've requested a once-and-for-all, definitive answer i'm afraid ;)

if anything you've only poured petrol on the fire - you've used lime mortar/bonding to allow the walls to breathe but then a sealer on top, be it PVA, SBR or acrylic is going to impair the breathability anyway so perhaps another kind of 'breathable' sealer is required! just throw that into the mix....

...anyhow, in my opinion PVA is NOT the correct thing to use for sealing in this case. experts and engineers in the tiling industry have formulated tiler's primer, either acrylic based or SBR, it says tiler's primer on the tub and that's what it is.

if you are going to go out and spend money on something to seal your walls with then why even consider PVA when there are purpose made products out there?

well there you go. i declare myself definitive. (ducks down and waits for the backlash)
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Postby toplondonchef » Tue Mar 15, 2011 8:51 pm

Hi andypty
Yes your right, the use of PVA always seems to cause a lot of "debate" in nearly all applications. It's become a bit of a "marmite" product (if you know what I mean)

Anyway, PVA is not good when used on a plastered wall prior to tiling. It can stop the tile cement from forming a strong mechanical bond with the wall finish and instead just bond the tiles to the surface of the plaster, leaving a weak, potentially dangerous bond.
Especially not good when used in damp / high humidity rooms, ie your bathroom

Much better to either lightly score the plastered wall with say an old screwdriver, or if the plaster has been left with a highly polished finish, rough up the surface with a wire brush

Then seal the walls with either ACRYLIC or LATEX TILE PRIMER, following any instructions on the label
Also use a good quality, powdered, waterproof grout

Hope all goes well
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Postby chris_on_tour2002 » Wed Mar 16, 2011 10:56 am

the reason that PVA should not be used as a tiler's primer is that it is not waterproof, in fact contact with water will cause the PVA to become 'live', or to turn back into its liquid state. you can prove this to yourself by peeling away some of the clear, set glue from around the lid of the bottle and immersing it in a cup of water. in no time you will see it turn white and will eventually dissolve completely.

this can be a real problem in wet areas. moisture ingress will cause the PVA to fail and the tiles to fall off.

all primers form a barrier between the wall and the adhesive, be it PVA, latex or acrylic. with any primer the trick is to apply just the right amount at the right dilution to seal the wall without creating an extra layer/additional potential failure point.
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