25mm plywood floor or hardibacker overboarding in bathroom?

Discussion in 'Tiling' started by Meerkat1, 7 Jan 2011.

  1. Meerkat1

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    What is best for tiling a bathroom: 25mm plywood floor or hardibacker overboarding on 18mm floorboards? Ceramic or porcelain tiles, with joists at 40mm centres. My builder seems dead against hardibacker as he says it has a tendency to crack and therefore isn't suitable for floors. I wonder if it's the cost, but I thought plywood was about the same price...??

    Also, on the subject of plywood floors, my builder has fitted 25mm plywood sheets in the kitchen at my request (fitting quartz tiles on floor). With two wet appliances on the plywood floor (sink and dishwasher), was wondering if anyone has any suggestions about protecting the kitchen floor?
     
  2. Richard C

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    If it’s a new floor, I can’t see the point of fitting 18mm ply & then overboading with Hardibacker unless your constructing a wet room but then you can tank the ply anyway; I’d go with 25mm ply every time. Structurally one board is always going to be better than 2 boards making up the same thickness; why have 2 boards when you can use one but make sure it’s WBP not ordinary ply. There should be no problems with Hardibacker cracking if it’s properly fixed, glued & screwed.

    Sorry I don’t really understand your question, what are you concerned about protecting the kitchen floor from, water? Make sure he uses WBP ply.
     
  3. Meerkat1

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    Builder says it's not WBP, which is really concerning me now. He says it's some other sort of plywood '3 times the price of ordinary plywood' but not marine plywood?? Here's a photo of the label on one of the plywood boards (which happens to be underneath the sink). Incidentally, this one looks different from the others (distinctly different colour, darkest board in bottom picture). Does this label look like the waterproof kind...?


     
  4. xr4x4

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    best way to tell if its waterproof is put a small puddle of water on it, if it sits there for hours it waterproof, if it soaks in, its not...!!
     
  5. Meerkat1

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    Okay, left a few strategic puddles on different patches will check on them later.

    Thanks alot :D

    Am I going a bit OTT with idea of WBP in kitchen with sink and dishwasher, or should I really be worrying about that for bathroom?
     
  6. Richard C

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    No, no, no, that won’t tell you anything; WBP (water & boil proof) also know as external grade ply will still absorb water/moisture the same as any other ply, it’s the adhesive that’s use to bond the wood veneers that waterproof so it won’t fall apart if immersed in water.
    What sort of ply? Can’t tell from that what that is! All the major tile adhesive manufacturers specify either WBP or Marine ply as a tile base & you should ONLY be using this as a tile base, if you tile onto conventional ply you’re risking not only tile failure but de-lamination of the plywood itself & you definitely not going OTT with WBP in the bathroom either. You don’t need marine ply either; WBP is made using similar waterproof adhesives but doesn’t have the expensive face veneers. I would rather see it replaced with WBP but if your stuck with it then you should go back to using Hardibacker over it (maybe that’s why he specified it in the first place) but even they specify WBP as a base; another option would be to either tank it or overboard with something like Marmox.

    Something you should know is that waterproof adhesive & grout (except expensive epoxy products) is only waterproof in the sense it won’t dissolve when wet, it still absorbs water. That’s why it’s important that any tiles surface continually exposed to water is itself waterproof & dimensionally stable when wet (plywood isn’t). WBP (or Marine) ply is perfectly adequate for floors that are not constantly exposed to water (i.e. a wet room) & when waterproof add/grout is used will easily cope with water from splashing, normal mopping/washing & the odd spillage.

    I would advise you read the Tiling sticky & Tiling Forum archive posts before you go any further, it may prevent you (or your builder) from making more potentially disastrous & expensive mistakes.
     
  7. Meerkat1

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    This is soooo frustrating! :( The whole reason for lifting the floorboards was to put down a more suitable substrate and now it still seems like the wrong one!! Is WBP more expensive or what? Can't understand why he didn't just get the right stuff in the first place! I am seriously miffed. Think I'm going to have to put my foot down hard on this one. I've purchased tanking kits for the bathrooms, think I'll have to do the same for the kitchen now!! Any suggestions regarding suitable tanking for kitchen floor (apprx. 18m sq) without raising level too much (fitting natural stone tiles 10mm thick)?
     
  8. tictic

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    for natural stone,for what materials you have i would spec...

    25 wbp ply screwed to joists every 150-200m with added dwangs to,
    seal the ply with sbr underside and egdes proir to fixing down,
    with natural stone tiles i would spec a uncoupling membrane...ditra...as you will have slight movement in the floor,

    then use a white flexiable RAPIDSET adhesive(so you dont get any bleeding through to the tile face)...

    and a flexiable grout also.

    you will want to seal the tiles before fixing or work very cleanly wiping the tiles as they are fixed..

    then when fixed seal them,
    grout them,
    seal them again just follow mfr inst..re:sealer that you use (for a natural stone).
     
  9. Richard C

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    Interestingly someone else has just asked how to tell WBP from standard ply; I admit didn’t know the answer so did a search & found this old thread which may help;
    http://www.diynot.com/forums/viewtopic.php?p=352340

    WBP is more expensive than standard ply but not as expensive as Marine ply. His reasons for not using WBP may be that you didn’t specify it & he’s just picked the cheapest. If he knew you were tilling, he should have know to use WBP ply; either doesn’t know the difference, hoped you wouldn’t notice or doesn’t care!

    If you’re stuck with it, you could use either a physical or liquid tanking membrane to avoid water being drawn into the ply; an SBR primer/sealer over the ply may work but I can’t say.

    tictic; problem is the OP's dippy builder has laid standard ply not WBP or Marine :rolleyes:
    I have contacted BAL for advice but have not had any response yet.
     
  10. Richard C

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    Right; got the following from BAL Technical but I suspect other manufacturers will most likely offer similar advice. It’s not exactly good news I’m afraid :cry: ;

    Please find attached a copy of our recommendations for Tiling to Timber Floors for your information;

    In order to guarantee longevity of tiling, we would advise that the existing plywood is overlaid with a moisture stable board of a suitable thickness. This will:

    1) Reduce the risk of movement/deflection in the floor which would be detrimental to the tiled finish
    2) Providing a substrate which can be tiled without the risk of the boards undergoing distortion before or after completion

    Priming the existing board with undiluted BAL Prime APD will help to seal the plywood surface, however this will not ultimately protect the boards from atmospheric moisture.

    We hope this information is helpful.

    Thanks and regards.

    David Wilson
    Head of Technical Services


    I did think the solution might be priming (sealing) with an Acrylic (APD) or SBR based primer or even tanking but BAL don’t seem to support this, recomending an overboard. They may be taking a cautious approach due to their warranty but I’ve never tried to tile over standard ply so I wouldn’t like to give you any rersonal guarantees either.

    Meerkat1 BAL also sent me a technical publication which, if you respond to my friend request, I will forward on to you. ;)
     

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