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How to apply a coat of multi finish....pls help :-(

Discussion in 'Plastering and Rendering' started by callard, 28 Nov 2007.

  1. callard

    callard

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    Hi......

    I was hoping to tile onto bonding plaster that i put up when the old plaster and bonding came away in the bathroom when i removed the tiles (2 small areas of 2 X 3 and 2 X 2, feet not inches :D )....not the whole wall, but i have been advised on this forum that it is not right and i should tile onto a top skim, which is fine with me........ but.......

    1) Am i right in thinking that i should pva the bonding plaster (bonding has been on wall for about 2 weeks now and is fully dried) let it dry then pva again and put my 2/3mm multi finish skim on whilst still wet/tacky?

    2) As i was hoping to tile straight on to the bonding in the first place i finished it quite smooth, would i need to scratch and rough it up a bit? i was going to get some Thistle bond-it (if thats the right stuff?) but i don't need a 10 ltr tub, for this small area i guess even 1ltr would be more than enough, and it seems such a lot of money for something that i won't use again.

    ......And finally, i am just a diy-er who gets enjoyment out of doing my own work and i am by no means a plasterer (if it was not going to have tiles put on top i would have got one of you guys in for a professional job :D) But something concerns me..........how can a 2/3mm skim be stronger than a 8/10mm bonding, i understand that when done i will have around 12mm thickness but is there a danger that the 2/3mm skim could come off with the weight of the tiles? or does 1 top skim really bond well into bonding plaster? being that it is only in some areas and not the whole wall that i will be plastering, obviously i will butt up to the existing plaster that is good and make smooth....well hopefully smooth :D

    Many thanks in advance for all advice
    callard.
     
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  3. joe-90

    joe-90

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    There's nothing to stop you tiling onto bonding plaster. Simply PVA 3 to 1 and let it dry. Tile on top of that.
     
  4. callard

    callard

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    Hi Joe....

    If it is correct what you say(and i don't doubt that you are giving me advice that you believe to be incorrect) then why do others say on these forums that you should never tile on bonding plaster as it is not strong enough to hold tiles and never never pva before tiling in a bathroom as when the pva gets wet it reverts back to a weakened sticky substance?

    Is it a case of what should be done in theory but what works in practice?

    I am more confused than ever now :(
     
  5. joe-90

    joe-90

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    I renovate houses for a living. They are talking twaddle.

    Didn't the tech guys at Unibond tell you the same thing?

    Believe me when I say that tile adhesive will stick to bonding far better than a skim coat will stick to bonding - that's what it is designed for. Ask the other guys why a 2mm layer of skim will grip better than tile adhesive. Even if you do apply a skim coat you still need a PVA layer to make the skim stick - so they simply have no argument about using PVA.
     
  6. MrTeeny

    MrTeeny

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    I've always tiled direct to bonding and never had any problems - like joe says pva is fine it's not like you're putting on a thick coat and you've the tiles and the grout to stop it getting wet.

    I've usually tiled direct onto the bonding without pva just wet the bonding first to stop the suction - last house they were still n the wall when i left after 9 years so you gotta remember tile adhesive is pretty strong stuff just make sure you pva or wet the bonding before tiling.
     
  7. callard

    callard

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    Hi Joe/Mr Teeny thanks for the info........

    You are quite right about unibond saying to use to use pva before tiling but as per the advice i got on here in my posting in the tiling section i have now got some Bal white star (and Bal do not reccomend to pva before tiling) because this pva thing is so hit and miss on here i rang them today to ask why and they said that some pva (not all) has in the past reacted with the adhesive and turned it into a wet substance as it absorbed the water in the adhesive, so thats the reason they say not to tile onto pva with their adhesive.

    I have also been onto British Gypsum and ask why they say not to tile onto bonding and they said it is a British standards thing regarding strength and porosity.

    But between the lines today between Bal and British Gypsum i have kinda come to the understanding that it would be ok to skim a little of the white star adhesive over the areas that i have used bonding plaster and once dry then tile on top of that.

    Does this sound ok to you?
     
  8. joe-90

    joe-90

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    Yes that sounds fine. It's really not that critical. I've been tiling for decades and never once had a problem.
     
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