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Waterproofing over existing plaster?

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  1. #1
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    Default Waterproofing over existing plaster?

    Our ensuite will be created from an existing bedroom, and we hope to leave the plasterboard intact. It's in good condition overall although painted.

    We are wondering, from a waterproofing point of view, whether or not we can waterproof directly over the painted plasterboard (and no, it's not wet area plasterboard)? I suspect that the painted surface (flat acrylic, I believe) would cause the membrane to lift/bubble and being a regular plasterboard will simply be an invitation for moisture troubles down the track.

    I know it would be acceptable also to villaboard over the top of the plasterboard, then waterproof before tiling.

    Your thoughts?
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  2. #2
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    Regardless of being able to waterproof over the paint - I would be concerned with the issue that effectively you have the weight of the tiles, tile adhesive waterproofing and paint all hanging off the bond of the paint to the plasterboard......

  3. #3
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    Quote Originally Posted by an3_bolt View Post
    Regardless of being able to waterproof over the paint - I would be concerned with the issue that effectively you have the weight of the tiles, tile adhesive waterproofing and paint all hanging off the bond of the paint to the plasterboard......
    Nah - the tiles apply almost no outwards forces - each tile sits on the tile below - the equivalent is a brick wall. The predominant force is shear and surprising as it might seem paint can withstand a lot of shear - as can the cardboard held in place against the gypsum plaster. Sure - pull outwards and it will tear off easily enough, but that's not what is happening with tlles on a wall. Even with fittings like ceramic foot rest and soap holders - so long as they are allowed to cure properly most of the forces are down not out, although too much pressure or weight and they will pull off the wall.

    In any case I would villaboard over the top better still remove and replace with cement sheeting - I'd be insulating too.
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.

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    Quote Originally Posted by Bloss View Post
    I would villaboard over the top better still remove and replace with cement sheeting - I'd be insulating too.
    This was my thought, to be honest. And as the exterior cladding is going to be totally removed and replaced with zincalume, insulation is going to be easy, and not negotiable anyway.
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  5. #5
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    Going over the top would be easier. OK What weight of Villaboard, 4mm/5mm/6mm ?/ All else being equal I'd go for the cheapest of course

  6. #6
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    so long as you fix it properly just get the cheapest (and that's not always the thinnest . . . ). 4.5mm I think is only sold in Qld, never seen 4mm? I'd use 6mm - can't use self embedding screws in the 4.5mm either.
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.

  7. #7
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    Do not tile over standard plasterboard sheets in a shower, or even a bathroom for that matter.

    They have no WR rating and are doomed to fail with a very expensive fix.

    As a professional waterproofer myself I can assure you I see this problem all the time, a sinke pin hole in a plasterboard sheet will turn into mush, and other walls in the batroom will covered in mould in no time as well.

    The price of a few sheets of Villaboard that can be fixed directly over the existing plasterboard is more than worth the effort.

    There are WR rated sheets for wet areas that look just like plasterboard but for the material on the face of the sheet (the wet side), it's thiker, harder and has fibres in it not just paper as with plasterboard.

    Don't do it.

    PS Waterproofing standards clearly state all wet areas MUST have WR (water resistant) sheeting on all walls. And remember the Standard is the MINIMUM REQUIREMENTS.

    Good luck.
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    http://www.wet-seal.com.au/waterproofing/locations.html

  8. #8
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    Quote Originally Posted by Oldsaltoz View Post
    Do not tile over standard plasterboard sheets in a shower, or even a bathroom for that matter.

    They have no WR rating and are doomed to fail with a very expensive fix.

    As a professional waterproofer myself I can assure you I see this problem all the time, a sinke pin hole in a plasterboard sheet will turn into mush, and other walls in the batroom will covered in mould in no time as well.

    The price of a few sheets of Villaboard that can be fixed directly over the existing plasterboard is more than worth the effort.

    There are WR rated sheets for wet areas that look just like plasterboard but for the material on the face of the sheet (the wet side), it's thiker, harder and has fibres in it not just paper as with plasterboard.

    Don't do it.

    PS Waterproofing standards clearly state all wet areas MUST have WR (water resistant) sheeting on all walls. And remember the Standard is the MINIMUM REQUIREMENTS.

    Good luck.
    I figured you'd say this...was waiting for your comments, actually. Ted is trying to avoid removing the plasterboard, as it's well glued and screwed, and walls are plumb and flat so easily tiled. We'll likely use villaboard over the top, and re-do the cornices.
    I am not responsible for anything that Moondog says!

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