PVA and why you shouldn't use it as a tiling primer.

Discussion in 'Decorating and Painting' started by Mudster, 16 Oct 2005.

  1. Mudster

    Mudster

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    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.

    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.
     
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  3. Softus

    Softus

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    Thanks for this mudster - I'm just about to tile 21 bathrooms and this advice is going to be very useful :p
     
  4. Zampa

    Zampa

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    Thats very interesting actually..good read.

    Even if the manufacturers product was virtually the same as PVA the guarentee would still be invild because you have not followed the manufacturers instructions.

    I have had similar experiences with ready mxed wallpaper paste.
     
  5. psc3239

    psc3239

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    I've just stimbled accross this post and exactly that happened to me a few years ago when my bathroom was renewed, i replaced some of the plaster board in the shower cubical as it had got wet with some of that marine ply, sealed it with unibond PVA then tiled and 6 months later the tiles started coming off. Had a rep out fron Unibond as i'd used their tile adhesive and grout, and they paid for new materials to re do the job. Funny thing is i told the bloke exactly what i'd done and he didnt pick up on the PVA thing.
     
  6. Mudster

    Mudster

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    Unibond are one of the largest producers of PVA in this country, they are the only manufacturer that still recommend it is used with their tiling products.

    Ardex, BAL, and Nicobond, the three main producers whose products I use, all specifically say don't use it, in fact it invalidates any guarantee these manufacturers offer.
     
  7. jbonding

    jbonding

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    what did he say the problem was?
     
  8. knownothing

    knownothing

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    So can you put tiles and tile adhesive straight onto plastered (once dried) walls?

    The misconception must be that dust from surfaces stops stuff sticking and so it needs priming with 1:5??!?
     
  9. Mudster

    Mudster

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    You use a tiling primer designed specifically for this application, BAL APD, Ardion 51 or similar, depending on which adhesive your'e using.

    This will stop the suction, but witht he correct primer it won't go live on contact witht he water contained in the adhesive.

    Just don't use PVA.
     
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  11. JayS

    JayS

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    Thanks for this thread Mudster, I've been wondering about why people go on about using PVA to seal with...now I know I was right not to use it! :)

    It normally states on the adhesive tub or bag what you should use as a primer, if any.

    If you're tiling onto a concrete floor do you need a primer at all?
     
  12. Mudster

    Mudster

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    You don't specifically require a primer the same way as you would for a plastered wall. But if you have a very dusty screed or concrete substrate this may impair bonding.

    You can wash over this with BAL SBR which is a cheap bonding agent for flooring. If it's particularly bad you can mix this in with some flooring adhesive to make a slurry mix and pour this on the floor and brush it around.

    This bonds all the dusty particles together with the floor and gives you a stable base.
     
  13. jbonding

    jbonding

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    pva will also do the job this will seal the floor also , i tiled my floor sometime back i mixed pva with cement and a hand full of sand and applied with a roller, left it to set the next day, sealed again with pva 5-1 to kill any dust tiled it and its been sound.
     
  14. Mudster

    Mudster

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    Gravity has probably helped a great deal in keeping your floor in place.

    It's unsound advice to use PVA under any form of tile adhesive for the reason explained above, it does actually stop a large proportion of the adhesive bonding to the substrate.

    BAL SBR is designed for this very purpose and is about the same price as a bottle of PVA, so no reason at all not to use the correct product.

    SBR is actually a form of PVA if I understand correctly, but it has other chemicals in it which stop the liquid going live again on contact with water and modify it for use in it's desgined conditions.
     
  15. JayS

    JayS

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    Thanks Mudster, that was pretty much my understading from reading the recommondations from BAL in their fixing guide. :)

    Ehhh.... Have you read this thread jbonding? It basically says do not use PVA...
     
  16. jbonding

    jbonding

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    thats why i say mix with cement and sand and this has the same effect a sbr it stops the pva coming alive, its been done for years before they put it in a fancy tub and renamed it. applying with a roller and the sand will provide the key.
     
  17. Mudster

    Mudster

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    [/quote] thats why i say mix with cement and sand and this has the same effect a sbr it stops the pva coming alive, its been done for years before they put it in a fancy tub and renamed it. applying with a roller and the sand will provide the key.[/quote]

    Actually if you take a look at the post you made on the rendering thread where you cut and pasted the PVA breakdown of / uses from that university type, you'll find that SBR is a polymer modified version of PVA, in so much as it has other chemicals in it.

    Adding sand and or cement to PVA isn't doing the same thing. The fact remains that PVA isn't compatible with tile adhesives full stop, you seem to be struggling to grasp this idea.
     
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