New shower pan on pre-sloped concrete

Discussion in 'Shower & bathtub Forum & Blog' started by MrJuicy, Feb 19, 2011.

  1. MrJuicy

    MrJuicy New Member

    Messages:
    2
    Location:
    Holladay, Tn.
    WHen building the waterproof membrane layer on a pres sloped slab, how thick does the setting bed need to be? I found in a B & D tile book, they say have two layers on top with lathe in between, is that only for wood floor applications? And is the deck mud available ready for h2o & mixing? As I understand it, I will be skipping steps 1 & 2............since the slab is presloped to the proper angle. I also plan to use a liquid membrane on the walls(cement board) before I start tiling them.
    Many Thanks

    Basically, a traditional shower pan is composed of 5-layers (well, six if you consider the first):
    1 - a bonding agent to make sure the next layer sticks to the slab
    2 - deck mud (mix of sand and portland cement) shaped with the proper pitch to the drain at 1/4" per foot from the longest distance. This can get messy if the drain isn't centered.
    3 - the liner
    4- the setting bed - another layer of deck mud (actually parallel to the sloped layer - i.e., equal thickness)
    5 - thinset to hold the tile down
    6 - finished tile.

    There are also special considerations to ensure the curb remains waterproof and you can tile it. Over concrete it's good to use bricks or pavers to make the curb rather than wood, which is often used over a wooden subfloor.
    Last edited: Feb 19, 2011
  2. Will Rogers Plumbing

    Will Rogers Plumbing Plumbing Contractor

    Messages:
    57
    Location:
    Moore, Ok
    If you could be a little more clear on what you are doing I could help you out.

    Based of your post.

    1. when setting a mud bed on a slab you don't need a bonding agent. Just clean up concrete well with water and sponge then apply thinset to the concrete and put the deck mud on the wet thinset. But in all honesty, that would be over kill. Just pack the deck mud right on the concrete.

    2. yes you do want to have 1/4" per foot slope. I make the pre slope atleast 3/4 inch think.

    3. correct, pvc liner goes on top of the pre slope

    4. the final layer of deck mud should be thicker than the pre slope.

    5. correct

    6. correct

    Wall and Curb mud is not deck mud. It's call "fat mud" and is mixed with lime to give it more cling.

    Hard to tell if your asking or give advice...
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    You can use thinset as a bonding agent, or just mix some portland cement up as a slurry and paint or trowel it on. It does help.

    You want your setting bed to be around 1-1.25" thick so it has some strength. Keep the weepholes clear so it can drain (unless using a surface membrane, which you don't appear to be doing). No need for lath over a concrete slab, although you'd normally use some over the curb. If you use a surface membrane (Hydroban or Kerdi for example), you only need one layer of deckmud.

    You can buy sandmix, but it is generally about 3:1 sand:cement, and it works better if it is closer to 4-5:1. The more portland cement, the stickier it is, the harder to get it to slope and pack, and it can shrink and crack more easily than when you have more sand. Don't mix it too wet, either. It should be wet enough where you can grab a handfull, squeeze it into a lump without water dripping out, and have it stay together when you let go. If it doesn't stay together, it's not wet enough. If it drips, it has too much water. You need to use something like a hoe or rake to mix it up...you can't reliably mix it with a drill and paddle like you can with thinset.
  4. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,161
    Location:
    North Vancouver, BC
    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
  5. MrJuicy

    MrJuicy New Member

    Messages:
    2
    Location:
    Holladay, Tn.
    More helpful information:

    Thanks for you help, I assume thinset as a bonding agent, is to secure the vinyl membrane in place on the slab?
    If need be, I will add more portland cement, by weight, to the sand mix purchased from L's.
    THe clamping drain is positioned to be level with the concrete @ the fixed flange, to prevent covering the weepholes do I stop the setting bed layer at the flange?
    I can increase the slope when applying the setting bed if need be(?) since I am framing the walls up to my needs.
    The membrane was purchases at THDepot but they do not carry the inside curb corner cover as I have seen in tile books.
    I am thinking I will apply two coats of Rd Guard to those areas to seal them, while applying it to the cement board on the inside walls.
    On the curb, do I form the lathe & lay it directly on the membrane then apply the deck mud layer?
    THe preslope is 4" thick, is making the final layer that thick, really needed?

    Again, many thanks for all the help & I am asking for advice.........*S*
    I will add a pic as soon as I have the walls framed up.
  6. Will Rogers Plumbing

    Will Rogers Plumbing Plumbing Contractor

    Messages:
    57
    Location:
    Moore, Ok
    another thing you may not know, but if your doing a surface applied membrane(kerdi, hydro ban/barrier, etc) then you won't want to use a standard fha shower drain. There is a way to use a standard drain with surface membrane, but it would most likly be out of your league.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    If you are going to lay the liner on the sloped concrete floor, then you do not need any bonding agents at all and neither of those would work on the liner anyway. Lay it down, fold the corners and get it as smooth as you can (when you pack down the deck mud, this should flatten it out). If you make it the 1-1.25" thick, you'll have plenty of weight on it to hold it in place. Tack it up on the walls only on the upper edges (above the curb height) so you don't compromise it. If making a curb, use the corners and glue them in place with the special glue.

    You have the items wrong...the sand mix is mostly sand. The prepared bags of sand mix have too much portland cement in them, you need to add more SAND, not cement to lean it out. This makes it a bit more porous, less sticky, and it packs and smooths better. Plus, it isn't as likely to shrink and crack as when it has more cement in it. IOW, a 3:1 sand mix from the bag needs more sand to make the ratio closer to 4:1 or 5:1 (sand/cement).
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