P.v.a. Versus Primers...... - TilersForums.co.uk | Tile Forums

**Dave** · 04-08-2007

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.........DAVE.....

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

PVA - Why you shouldn't use it as a tiling primer
This article has been written by Alan at AT Stone who is a Professional Tiling contractor, He now mainly specialise in natural products but over the years He 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 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.

**enduro** · 04-08-2007

Very good dh, hopefully people will read and learn, and not read and weep when they have used pva and all the tiles fall off.

**devonmark** · 04-08-2007

regarding pva on fresh plaster, many decorators coat new plaster in the stuff to seal, all they are doin in effect is sealing in moisture as it takes a good 4wks for the plaster to dry thoroughly. Fresh plaster should be primed/sealed with contractors emulsion 50/50 with water when decorating.

just a bit of useless information that may come in handy.

**Dave** · 05-08-2007

Cheers lads ...just thought this article was ideal for the pva versus primer argument that keeps cropping up....

**brian c** · 05-08-2007

top man Dave

**Varley** · 06-08-2007

Good thread Dave

Jeffrey4670 · 07-08-2007

Hi, This is very interesting! In the past I have used PVA, but not any more. Over the past few jobs I have used BAL Bond and with a bit of luck the floor tiles will stay down!!! Jeff
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Hi, Please could I ask you this question! I have read that you must seal the underside/joints of ply overlay. Why is is this so? for dampness? Is it ok to use PVA? Jeff

**Dave** · 07-08-2007

You prime to minimise moisture absorption.. so pva wont suffice as primer.......

anne0411 · 07-08-2007

Great thread thanks!

barriesheene · 08-08-2007

Have to be honest that this came as a surprise to me on the BAL course I sat. I had been told so many times over the years as a tile salesman by RESPECTED tiler's that there was no need to, and i quote " use that overpriced s*it " when pva will do !!

**Dave** · 08-08-2007

it is pricey stuff barrie mate.. but cheaper than a re-tile if they fall off...lol lol...

**Matty A** · 23-10-2007

I was looking in tile suppliers near where i live and asked only this morning how much a bottle of primer was now of course they had the dreaded pva but also sold everbuild SBR and i was wondering if the sbr is ok as a primer as it is only £11 + vat for 5ltr bottle cos i have a large job next week that all needs priming.

Cheers
Mat