tilling over hardwall in bathroom Page: 2

[6spidermonkeys]

to all
can anyone tell me if its ok to tile over hardwall plaster which is going to be wher the new shower will be .the area is about 2.5 high and 600 wide .should i just hack it off and sand and cement it. or am i just being paranoid. cheers

 

[6spidermonkeys]

sorry if i appear a bit naive but whats the problem with pva cheers alan

 

[Bubblecraft]

When you treat a surface with PVA it partly soaks in and parlty sits on the surface of the substrate much in the same way as wallpaper paste.

If PVA gets wet it becomes slightly live again, it doesn't completely return to it's liquid state but it becomes sticky.

When you spread tile adhesive onto the wall or floor, the water in the adhesive makes the PVA live and stops the adhesive from penetrating the substrate and providing a mechanical grip. Basically your tiles, grout and adhesive are being held to the wall or floor by a thin layer of PVA.

Most tile adhesive works by crystalising when it sets (some are slightly different such as epoxy based ones) but generally they all work the same way. Once the adhesive starts to set, crystals from and expand into any imperfections in the substrate surface (at a microscopic level) to create a grip. PVA stops this process by creating a barrier between the substrate and the tile adhesive.

Dedicated primers soak right in to the substrate and stop the sponge like "draw "effect but they don't coat the surface in any way, they are an impregnator as opposed to a barrier.

Hope that clears things up

 

[6spidermonkeys]

thanks mate

 

[6spidermonkeys]

can anyone recommend a suitable primer for the rest of the wall regards alan

 

[Bubblecraft]

What is the substrate made of or do you mean the new dot & dab wall?

 

[6spidermonkeys]

the rest of the wall is a combination of finish plaster and sand and cement ,plus the area where the shower is to be fitted is wbp ply cheers alan

 

[Bubblecraft]

Bal SBR mate. What size of tile are you using?

 

[Bubblecraft]

When you say "Sand & cement" is this an area that was recently done or is this an old scratch coat from under blown plaster?

 

[6spidermonkeys]

400 x 250 x 7mm ceramic cheers alan

 

[Bubblecraft]

If your sand/cement area is a smooth finish, you can use the SBR. If its a rough scratch coat or a bonding coat, this will need a skim or re-sheeted before applying an SBR coat.