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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

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.

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.

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.

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

top man Dave

Good thread Dave

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

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

Great thread thanks!

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 !!

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

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

some sbr's are just bonding agents for plaster and cement screeds etc and not primers as well.. read the bottle and see what it say's...........dave..

Cheers mate
This is off tech sheet




As an admixture for mortar/screeds/renders.



As a bonding agent for screeds/renders.



As a primer/sealer in tiling applications.



As a flexibliser for cementicious based tile adhesive when tiling on wooden/asphalt floors.



In addition, SBR Bond has the advantage over PVA bonding aids in that it is not adversely affected

in wet conditions and is therefore recommended for exterior use.
AREAS FOR USE

3rd one down what do you think, im thinking it ay be ok for the job the wals are painted i was gonna score them first as it seems to be on pretty damn good.

thats what you do with bal bond..good price that matty..........dave..

That'll dink dank do for me

cheers
mat

I have just read this after coating horizontal wood framing around a bath with Evostick waterproof PVA. I also went part way up the wall to cover a repaired area of lath and plaster. Should I remove it, and how?

Always said pva should be outlawed as a primer.........

Why spend a tenner on 5 litres of PVA, when you can get 5 litres of Nicobond acrylic for nearly the same price! I hate a certain builder who I have told time & time again not to use PVA.

Have been reading with interest many many posts and i have been taking note of a great many thing that i feel could / should have been included within a recent 2 week training period at an establishment highlighted in a not so encouraging light in the past on this forum. (i didn't know before i went down there is my defence!!!).

One great thing about the training was that i was introduced / recommended to check out this forum.
An example of some of the thinking where i was being linked to this topic. I raised the matter with my trainer and he vehemently rebuffed the argument against PVA and proudly declared his loyalty to the stuff and that he slaps PVA onto every surface. Something which i am quickly learning is not quite the recommended action.

Ah well, you live and you learn.

I was also told when i went on the Bal course never to use pva as it sits on the surface and doesn't inpregnate the substrate, when he showed us it just peeled off like a rubber film...nuff said eh!!!

I noticed that some of Topps adhesives (tubs) specify the use of PVA as a primer!

(sorry Gaz!)

Originally Posted by Grace'sDad

I noticed that some of Topps adhesives (tubs) specify the use of PVA as a primer!

(sorry Gaz!)

Could you be more specific Mark...Toppfix ?...if so which ones ? maybe I can clear it up....Gaz

great post m8.

I've stuck this thread again due to the amount of people using the term PVA instead of Primer just recently. I hope you all use Primer and NOT PVA!

I've read numerous discussions on the use of PVA on these forums during the relatively short time I've been a member. Let me get something straight; When you say PVA, do you mean polyvinyl acetate?

If so...

WHY would ANYONE think using wood glue as a primer is a good idea?

I'm really curious about that.

/sWe

I think you need to wait for a response from the plasterers on here for that sWe.

That's exactly the point. A training centre has even been quoted using the term during a course too I believe before now. It's just not a done thing in my eyes no matter what is says on the bag of adhesive (I think in that case in the training centres defense the lesser quality adhesive brand actually did quote it on some literature - bless them).

Never PVA though. Always a non water soluble priming agent.

many decorators coat new plaster in the stuff to seal

Only the bad ones do! PVA has hardly any decorating usage, except as a size before wallpapering and adding to wallpaper paste when the paper is a real pig and wont absorb the paste. Its no good for painting on as it prevents the paint adhering to the surface properly. PVA should be left to the plasterers, even heard recently of some bloke who was told to mix PVa into his paint to help it stick - madness! And I only use primers when tiling you will be glad to hear

Few seem to bother actually reading the instructions and specs supplied by the manufacturers of the products they use. I wonder why it's like that.

It ticks me off.