![]() Never assume you know best !! as it's the tilers area of expertise ,and if you throw hat in to the ring then BEWARE ,if you are a Plasterer/tiler then you should get on the tilers forums two of them and educate yourselfes in the correct way of doing these jobs,like plastering in the last 10 year the ranges of materials and new thinking and systems have exploded ,i have to keep myself up-to date with the tiling more than the rendering,as it's moving so fast, and the reason i 'am on here is to try and get with it on the plastering scene ,from talking to you lot and the sponsors with is great and slowly working ,but i still have no idea about the machine's for plastering like some of you guys, i'am 53 so an old timer ,in that sense ,having said that ,i have probs forgotten more than some of the F on here LOL, my way of approaching other trades is to ask them ! they should know, and never get involved in there job's and liability !!.Click to expand.Yeh i think so too, was hoping to give it a go as have done tiling a few times so that wasnt my concern it was more the straight walls. S & C is the best sub straight to tile onto every time !! which i do a lot as i render/screed my own swimming pools before appalling mosaic to them ,first of all there is a scale of sub straights and the correct tile weights each can take, ( i will post later ) cement based adhesive /grout is never waterproof and just for your information nether are most tiles/stone so water in very wet areas like showers/bathrooms /splash backs /wet-rooms are subject ,to prospective damage by water/steam/moister ,if you use PVA in any of these situations you are asking for trouble ! and when it comes if you have PVA'd it then the buck stops with you so as spreads These are not my words ,but i have copy and pasted for you. So only use PVA before tiling if the adhesive manufacturer specifies it in the instructions. I hope this clears up any misunderstandings. They also stop a chemical reaction occurring between the cement based adhesive and a plaster substrate, a known problem know as "Ettringite failure" Ok so what's the difference between this and Ardex or BAL primer, well basically the tile manufacturers 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. PVA stops this process by creating a barrier between the substrate and the tile adhesive. 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. Most tile adhesive works by crystallising when it sets (some are slightly different such as epoxy based ones) but generally they all work the same way. Basically your tiles, grout and adhesive are being held to the wall by a thin layer of PVA. When you spread tile adhesive onto the wall, the water in the adhesive makes the PVA live and stops the adhesive from penetrating the substrate and providing a mechanical grip. 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 treat a surface with PVA it partly soaks in and partly sits on the surface of the substrate much in the same way as wallpaper paste. We had Ardex Technical down to the site to compile a report, the basis of which was it's the PVA that causes the problem. I tiled it and 6 months later every single tile fell off the ply, the adhesive solidly stuck to the tile but came clean a whistle off the ply. Thinking he was doing the right thing, the builder got his guys to seal the ply with unibond PVA.I wasn't aware of this. OK why then? Well I asked this question to Ardex when I once had problem, I'd tiled a bathroom that had been constructed in 25mm Marine ply. ![]() All three of them have one thing in common, they all specify that under no circumstances may PVA be used before using any of their adhesives. Their products are similar in many respects, sometimes one will make products the other don't, and I also find some of there products more useful in different applications. For me to be able to give guarantees I need to follow strictly the specification of the adhesive manufacturers.Īrdex, BAL and Nicobond are the three suppliers I use most. I have to give guarantees for my work (many of these projects are commercial such as sports centre showers and changing rooms). PVA - Why you shouldn't use it as a tiling primer
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