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Waterproof / cement base - what to do first ?

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  1. #1
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    Default Waterproof / cement base - what to do first ?

    This is a diy bathroom renovation project, I'll remove all floor tiles, redo the cement base before tiling. Should I do waterproof on top of the new cement base or the other way round ?

  2. #2
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    On top of the new base. It should bea case of: everything else - waterproofing - tile adhesive - tiles

  3. #3
    Senior Member Batpig's Avatar
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    Dear Ecsk,

    Well, that is a very good question which has cropped up without a definitive resulting consensus in several threads here, most notably because:

    A) On the subject of the waterproofing of Wet Areas, the Building Code of Australia generally defers to the requirements of the relevant Australian Standard AS3740, which specifies that the Waterproofing Membrane should be installed on the substrate beneath the Mortar Screed. Indeed, "Wetseal" - who are probably Australia's largest Waterproofing contractor-franchise - adhere to this method, using their proprietary in-house green-coloured Polyurethane membrane...

    But, however...

    B) Australia's largest "actual" manufacturer (as opposed to "rebadger") of Polyurethane and other type Waterproofing Membranes - Parex Davco - recommend that their most-widely used product in this category, K10+, be installed on top of the mortar screed (That's probably the main reason why you're asking the question, hey...).
    Anyhow, guess what one of the two colours is that K10+ is available in? Yep - green...
    So guess where Wetseal gets it's "inhouse" Polyurethane from?... Yep, you got it...

    So the situation is, the relevant Australian Standard want's you to go underneath, while the largest manufacturer wants you to go on top. My take on the source of the discrepancy: I think that the said Standard is thinking too much along the lines of a practical "Trades" sequence. By going underneath with the Membrane, your Plumber or Waterproofer can come out in one sequence of visits and do everything necessary for your Tiler to then come out and do all of his things in one uninterrupted sequence of visits. Nice and neat, especially since you can often be waiting a few weeks for these different guys to turn up (how could you possibly coordinate them in an overlapping arrangement?...).

    But in going down this path, I think the Standard is underestimating the potential which exists for an odour to develop in a continuously-damp Screed over time. This underestimation is possibly because in the past - when waterproofing measures weren't employed quite so vigorously - moisture in the Screed might well have been escaping into the various building-elements that we are now trying to protect with the Waterproofing - ie. floorboards, joists, studs, etc. So your problem in the past might have more often been dryrot or termites, rather than a smelly shower-base...

    I therefore think Davco have got it right when they say go over the Screed with your membrane. It gives you the best of both worlds - protection of your frame, without the potential for a smelly shower-base. And it is particularly more do-able that way if you are prepared to do it yourself (which I believe might actually be illegal...). Make sure you give plenty of thought to your Puddle-Flange arrangement if you do...

    Best Wishes,
    Batpig.

  4. #4
    Golden Member arms's Avatar
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    Quote Originally Posted by ecsk View Post
    This is a diy bathroom renovation project, I'll remove all floor tiles, redo the cement base before tiling. Should I do waterproof on top of the new cement base or the other way round ?

    as batwig has said (somewhat drawn out ,but what the hey at least he answered),it all depends on who gets there first ,in my renovations i like the proofing to go below the screed ,but sometimes this doesnt always go to plan ,in my opinion it shouldnt really make any difference which order it goes in ,just as long as it goes in
    kind regards
    tom armstrong
    www.kitcheninabox.com.au
    Flat Packed kitchens to the world

  5. #5
    Rigid Member UteMad's Avatar
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    HIA supports a membrane on the slab and another on top of the tile bed.. It takes a bit longer and requires the tiler to come twice but its the best way..
    This is the way we will be doing the next few we are starting demo on on monday

    cheers utemad

  6. #6
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    I have the technical brochures for both CSR and BGC for their wet area solutions and both show the waterproofing under the mortar bed. When I came to apply the Dunlop water proofing solution it said in the instructions to put it on top of the mortar os I was momentarily stumped. I decided in the end to put it both under and over the mortar bed for extra security. I also have a plastic flashing under the fibre cement sheeting and behind the villaboard so nothing will get to the wall plates even if the membrane(s) fail.

  7. #7
    Try, Succeed, Success ! John99's Avatar
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    I did under the base and on top of it as well ....
    Thinking about mowing the lawn doesn`t get it done !

  8. #8
    Golden Member arms's Avatar
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    Quote Originally Posted by John99 View Post
    I did under the base and on top of it as well ....
    better do do it once properly than twice and cop the grief from the other half (better or worse)
    kind regards
    tom armstrong
    www.kitcheninabox.com.au
    Flat Packed kitchens to the world


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