Continuing tiling above bath on new-build plasterboard walls....

[lathe tiler]

Hahaha These self taught tilers

 

[lathe tiler]

Plasterers use pva to prime walls for a better key for sticking plaster has loads water in aswell wen it sets you can pour as much water on as you want it won't fall of the wall and won't go soft

 

[CJ]

There is enough info out and about that explains why you should NOT use PVA, but if people are so stubborn, or think they know best....then let them get on with it.

Here's more info.





See www.Mapei.co.uk for more information.


MANY PEOPLE THINK THAT P.V.A. IS OK AS A PRIMER ON WALLS AND FLOORS SO I THOUGHT THAT I WOULD LET YOU SEE THIS " LINK " AND HOPEFULLY IT WILL ENLIGHTEN SOME NEWCOMERS OR EVEN EXPERIANCED TILERS AS WHY NOT TO PRIME SUBSTRATES WITH P.V.A. INSTEAD OF PRIMERS.




P.S. I always prime with primers and this will show you why!!!!!!!




PVA - Why you shouldn't use it as a tiling primer


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 specify 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 partly 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 crystallising 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 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. They also stop a chemical reaction occurring between the cement based adhesive and a plaster substrate, a known problem know as "Ettringite failure"


I hope this clears up any misunderstandings.
So only use PVA before tiling if the adhesive manufacturer specifies it in the instructions.



If some don't or won't take note.........then so be it.

 

[Stef]

Hahaha These self taught tilers

Go on then enlighten us to your expert knowledge & let us know how you started off then?
Another tiler with x amount of years experience & too stuck in their ways.
How many have we seen coming through here????
You my friend are on a long list!! [emoji23][emoji23]

Read above what is stated & you might learn something...

 

[Deleted member 9966]

Right, enough tit for tat about PVA. If you have nothing useful to add for the person that started this thread then clear off and start a new thread about PVA and Primers somewhere else. This thread is now closed.