Best Wall Prep for Concrete Backer Board??

Discussion in 'Shower & Bathtub Forum & Blog' started by NoviceSF, Jun 25, 2006.

  1. NoviceSF

    NoviceSF New Member

    Jun 7, 2006
    So we are having the shower (over tub) redone in our new place.

    we don't know much about all this, but we have heard that there are basically two ways to set the new tile on the shower walls. It is a very old building (built about 1900), and a number of contractors have told us that the old way of setting the tile was to put a concrete mud on the walls first. They claim that this is the best for old buildings and that is the way it is "supposed" do be done. However, other people have said that concrete backed board will work just fine, and it is much cheaper. i have a tile guy that comes highly recommended, and he swears by concrete backed board. So we are going with that. concrete backed board, not the concrete mud (called "Scratch and Brown" maybe?).

    Since we are going with the concrete backed board, the only question that remains is how to propperly prep the walls for the board. I have heard a few different things from different people and i am now thoroughly confused.

    Our wall contractor (who is ripping out the existing walls to the studs and building a little shelf at the back of the tub) says that if if he sheetrocks, once the tile guy puts up the concrete backed board it will be too thick. so he said he would just apply two layers of Fort Fiber 60 minute paper to the framing and the concrete backed board could be applied over that.

    A different wall contractor (the one we are not going with because his bid was twice as much) said he would put in a Bituthene waterproofing membrane 12" high around the tub, put in a new paper membrane (which i assume is like the Fort Fiber 60), AND greenboard sheetrock around the tub.

    Our tile guy said he usually just puts up the concrete backed board over the sheetrock (i assume he means the greenboard sheetrock, but i guess he could mean regular sheetrock).

    The woman at the tile store told me to make sure that, if we are using concrete backed board, that we DO NOT use greenboard sheetrock under it, and instead coat the studs in a waterproof sealant and wrap them in roofing felt, and apply the concrete backer board directly to the studs.

    so as you can see, i don't know who to believe. now i am sure that there is more than one way to skin a cat, but i just don't want to give anyone the wrong instruction. i want to make sure that the wall guys finish the walls in the best way so that the tile guy can come in, put up his concrete backed board, and instal the tile.

    of course, i don't want the shower to leak. i don't want the tiles to fall off. but truth be told, we will probably be in this place for about 5 years and it is entirely possible that the next people will redo the bathroom. so it doesn't have to last 100 years.

    so, anyone know the best way to prep the walls for concrete backed board?

    any advice on what to do (or what NOT to do) would be great.

  2. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    "any advice on what to do (or what NOT to do) would be great."

    My advice is to go to and get real advice from the pros.

    I don't trust any of what you have to date and I would not add my wild guess to the mix.
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  4. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego, CA
    For detailed advice there are two excellent resources ...the Tile Council of America and their Handbook for Ceramic Tile Installation....and the internet forum

    I will offer some general comments: greenboard is not approved as a tile substrate in a tub or shower, and I have never heard of putting backer-board over anything like drywall or greenboard. There does need to be a waterproof membrane like visqueen or 15 lb felt beneath the backer board. The resources I mentioned have plenty of detail to offer.

    On tile jobs I have done at home, I take backerboard all the way to the ceiling. This eliminates an odd joint trying to take greenboard from the top of the shower up to the ceiling. You need to shim the studs for the backerboard so that it laps over the tub flange without having to kick it out. The shimming then would create a thickness problem when joining greenboard at the top.

    There are some modern materials avalable as well, so do a little research,.
    Last edited: Jun 25, 2006
  5. NoviceSF

    NoviceSF New Member

    Jun 7, 2006

    thanks guys. i did go ahead and post it on John Bridge.
    i have done research, but i am really a novice and don't know what is what. obviously i am not doing this myself, i am just trying to instruct my contractors. in addition to this kind of research, i am just going to make them talk to each other.

  6. NoviceSF

    NoviceSF New Member

    Jun 7, 2006
    is this similar to the Fort Fiber 60 Minute paper? or is this like the roofing felt that the tile lady told me about?
  7. geniescience

    geniescience Homeowner

    Nov 27, 2005
    humid summers hot, humid winters cold
    use what Jimbo wrote as your starting point. It is all correct. the guy you hired who said he would NOT put plasterboard up was right.

    i do know that the membrane works best when applied as close underneath the tiles as possible. So no to putting it on the studs, and yes to putting it on top of the backerboard or mud walls.

    Whether there are differences between these membrane products (like felt) is something you can ask on the other forum. I have been signed in at for a long time.

  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Unless you are going to use a waterproof membrane on TOP of the walls, you need something between the cement board (cbu) and the studs to prevent moisture from damaging them over time. So, water vapor barrier goes on the studs, then the cbu, then thinset and tile. Now, there are waterproofing things you can put on TOP of the cbu if you wish. One of several you can paint on is called Redgard made by custom building products (you can buy this at many tile stores, and HD carries it, not sure of Lowes). A tileable water proof membrane you can use is called Kerdi by schluter. If you use either Redgard or Kerdi, you would NOT put a vapor barrier on top of the studs prior to putting up the cbu - you don't want to sandwich moisture between the two.

    The whole reason for this is that tile and grout is NOT waterproof. Liquid water should not get there, but vapor may, and then with condensation, the moisture can be a real problem.
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