Dot & Dab on brick walls for NoMorePly - Tile Advice

[travispuk]

Hello everyone,

I am planning on using Dot & Dab with a Mapei single part flexible tile adhesive of 12mm NMP boards to a fairly rubbish brick wall. My plasterer (a really good guy) suggested I should PVA bond the brick wall prior to doing the d&d. I have done the PVA solution now, but have been spooked by a number of threads here talking about not using PVA for the prep. I know that these have mostly been relating to putting down tiles and tile adhesive, but was wondering if I should not be relying on the PVA bond on the brick wall for the d&d now?

Given that I have already used the PVA, should I also add a coat of SBR or will the PVA be fine for this application?

Thanks in advance.

ps. I have also used 5 x stainless steel screws for each board to provide a fixing to the brick wall. Primarily to assist in making a nice flat surface and positioning as the bricks are pretty horrid, not a problem in a 120yr old house that had a nice thick wet plaster covering.

 

[travispuk]

Anybody?

 

[turnip]

Why not use plasterboard or marmox? Nomoreply is a gypsum board if I remember right, last time we used it we had to prime each side before it came into contact with adhesive, so alot more work involved using this!

 

[White Room]

The Home Of No More Ply

 

[Ajax123]

Problem with Pva on a screed floor is twofold. Firstly it breaks down in alkaline conditions. The screed is alkaline as is the adhesive so it is sandwiched between two alkalis which can accelerate breakdown through electrolytic reduction. The reaction is more rpid in the presence of moisture. The second and more readily visible issue is that is tends to form a skin as the pore structure of the screed is generally such that the Pva is not drawninto its surface. If your brickwork is really rough there is a good chance that this will not cause a problem unless there is any damp present which will encourage the breakdown

 

[travispuk]

Thanks everyone for our advice.

Alex123, the brick work is very rough. The PVA seemed to soak in quite well and it had helped a huge mount with the crumbly mortar... not that there is any problem with the mortar.

My main concern was whether I should be able to put SBR over the existing PVA solution, or if I can leave the PVA and put he adhesive on top.

Turnip, I don't believe nmp is gypsum based, but it cement board.

Whitebeam, yes I saw the website and that was part of my concern resulting in the question.