Pva

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The link Warriour put up originates from the members section so maybe being a newbie he couldnt access it, ive posted several times on the subject so i am going to make a point of doing sticky on it when i get some time to myself as this subject needs clarification then people can make there own mind up dont get why a specialist would be asking this though
 
I ain't a tiler end certainly no specailist, when a substrate surface is treated with pva it partly soaks In and partly sits on the on the surface, if the pva surface layer gets wet it can become live again ie it reconstitutes ( becomes sticky again) and doesn't return ti a solid state. When the tile adhesive is applied , the water in the addi causes the pva to become live preventing the addi from penetrating the surface resulting in poor mechanical grip. Therefore tiles, addi and grout are being held ti the wall by a thin layer of pva . Instead you should invest in an sbr primer, as it soaks into the substrate and prevents the sponge like draw. However they dont coat the surface in any way because they are an impregnator as apposed to a barrier, all the same it is important to know that when using cement based addi it should not be applied directly to plaster substrate as it causes a chemical reaction known as ettringite failure....... is that me an expert now lol...... hope Billy hasn't fecked off.:RpS_lol::flapper:
 
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Good post Fatarm though i have put this info up myself before so it all needs to go into a sticky, i was talking to some tilers this week on site and there prep was proper and we all agreed that we had used PVA years ago cos that was all we knew and as far as we knew the jobs were all ok, the main problem seems to be a chemical reaction between PVA and cement, an alkaline thing which can cause failure as for that numpty earlier is that all this info is on the Tilers Forum but he is probably to specialised to go on it.
 
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