Don’t listen to that idiot on handyman can. lol He’s an idiot who doesn’t have a clue when it comes to tiling.
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 AND HOPEFULLY IT WILL ENLIGHTEN SOME NEWCOMERS OR EVEN EXPERIANCED TILERS AS WHY NOT TO PRIME SUBSTRATES WITH P.V.A. INSTEAD OF PRIMERS.
Dave Howe, Master Tiler, from TilersForums.com
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. .
PVA v Primer
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 v Primer.
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 v Primer 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 v Primer.
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 v Primer before tiling if the adhesive manufacturer specifies it in the instructions.
A while ago I wrote a post for another forum which explained the reasons behind not using PVA as a tiling primer, it is posted below for your information, I’ve been asked to copy it to various other forums and thought it might be useful here also. I hope it is of some help.
Oh and if you do require a primer then use one suitable for the adhesive you are using, such as BAL APD or Ardion 51.
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. PVA v Primer.
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 v Primer.
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. PVA v Primer.
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. PVA v Primer – Primer Wins Every Time!
ADDED BONUS 10 TIPS WHEN FLOOR TILING
Tiling Made Easy – 7 Tips For Beginners
1. Start small: Do not plan to lay tile in a large kitchen for your first project. Try a small bathroom first.
2. Watch a “how-to” video: Reading is great, but this is a hands on project, and there is no substitute for watching an expert at work.
3. Buy quality tools: A trowel that costs 30% less is not a bargain if it breaks halfway through your project. Buy the best quality that you can afford.
4. Do NOT buy a wetsaw: For your first project, hire a wetsaw. The less expensive models at the DIY store are not great quality saws. Spend less and hire a good quality wetsaw. If you find that your enjoy laying tile and plan to lay more in your house, then consider investing in a higher quality wetsaw.
5. Order enough tile: Take careful measurements and order extra tile. Tile is made in batches (like wool) and if you get tile from two different runs, it may not match. Allow for some breakage, and then allow some more if this is your first or second tiling project.
6. Don’t forget the trims : These you use to hide a tile’s unglazed edge and any cut tile edges.measure how much you need to compltete full length’s without piecing.
7. Have fun: Remember, this is a learning process. Tile experts charge a lot of money for a reason. It takes time and practice, but each room you tile will look better than the last.
I think I would buy a cheap wet saw these days, but a good blade.
