Sealing a skimmed wall
- Thread starter ron99
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mix pva 5-1 and give the walls a coat to control the suction giving you plenty of time for the adhesive to go off.
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Why not to use pva before tiling... courtesy of mudster
I took a look at the webstie you linked, this sadly is the misinformation I'm faced with on a daily basis.
I should expand on who I am and why I appear to hate PVA so much!
I'm a professional tiling contractor, I now mainly specialise in natural products but over the years I've stuck up (or down) every type of tile there is.
I have to give guarantees for my work (many of these projects are commercial such as sports centre showers and changing rooms). For me to be able to give guarantees I need to follow strictly the specification of the adhesive manufacturers.
Ardex, BAL and Nicobond are the three suppliers I use most. 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. All three of them have one thing in common, they all specifiy that under no circumstances may PVA be used before using any of their adhesives. If you do all guarantees are void.
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. 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.
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.
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.
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, 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 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.
Ok so whats 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.
I hope this clears up any misunderstandings.
re tiling....Courtesy of Mudster.
I took a look at the webstie you linked, this sadly is the misinformation I'm faced with on a daily basis.
I should expand on who I am and why I appear to hate PVA so much!
I'm a professional tiling contractor, I now mainly specialise in natural products but over the years I've stuck up (or down) every type of tile there is.
I have to give guarantees for my work (many of these projects are commercial such as sports centre showers and changing rooms). For me to be able to give guarantees I need to follow strictly the specification of the adhesive manufacturers.
Ardex, BAL and Nicobond are the three suppliers I use most. 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. All three of them have one thing in common, they all specifiy that under no circumstances may PVA be used before using any of their adhesives. If you do all guarantees are void.
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. 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.
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.
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.
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, 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 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.
Ok so whats 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.
I hope this clears up any misunderstandings.
re tiling....Courtesy of Mudster.
Good post legs-akimbo,
I always try and talk customer out of having tiles in the shower cubicle because I'm not happy until the manufacter design grout 100% waterproof, I know they are ways round it but I prefer the upvc sheet that design for shower cubicle which I have one myself for the last 12 years and it's the best thing I have done, with tiles you still get black moulds problem in grout as well unless it's kept clean by wiping the water everytime.
Basically with pvc sheet or waterproof wall panel shower is a tanking system inside the shower area without the tiles.
My own opinion though!
I always try and talk customer out of having tiles in the shower cubicle because I'm not happy until the manufacter design grout 100% waterproof, I know they are ways round it but I prefer the upvc sheet that design for shower cubicle which I have one myself for the last 12 years and it's the best thing I have done, with tiles you still get black moulds problem in grout as well unless it's kept clean by wiping the water everytime.
Basically with pvc sheet or waterproof wall panel shower is a tanking system inside the shower area without the tiles.
My own opinion though!
Excellent explanation legs-akimbo. I just couldn't be a*sed... 
Personally I don't use PVA to seal before paiting a wall or ceiling either, just give it two thick (or three thin...) coats of good quality paint instead. Works out a little bit more expensive, but makes it easier to cover any minor painting mistakes you "might" make.
I disagree mason. I think tiles are more durable if installed correctly with proper tanking of the wall etc. The PVC sheets have a very limited life span...very much like PVC windows which are a complete waste of time (and money) compared to hardwood...anyway that's a different story...
Personally I don't use PVA to seal before paiting a wall or ceiling either, just give it two thick (or three thin...
) coats of good quality paint instead. Works out a little bit more expensive, but makes it easier to cover any minor painting mistakes you "might" make. Oh wellJayS said:
My upvc shower panels is still as good as new from 12 yrs, maybe because it doesn't have the same damage effect from ultraviolet light from the sun as with upvc windows??
I agreed if the tanking is done correctly then shouldn't be a problem.
Another advantage is that the shower panels is cheaper & quicker to do but everyone preference is difference.
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cant take the credit for the aforementioned info.... It was a copy and paste from another forum by mudster.
masona said:Oh wellJayS said:
My upvc shower panels is still as good as new from 12 yrs, maybe because it doesn't have the same damage effect from ultraviolet light from the sun as with upvc windows??
Oh NO I did the whole shower room @ home with them...shall I paint the window black ,or brick it up...might live more than 12 years
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