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-   -   Taping cement board joints (https://www.askmehelpdesk.com/interior-home-improvement/taping-cement-board-joints-12327.html)

  • Sep 1, 2005, 07:44 AM
    ikkyu
    Taping cement board joints
    Does anyone know what kind of compound to use on cement board?I've checked the USG FAQ site and they recommend 'glass tape for the joints, I see no mention of compound, other than to say that joint compound is not acceptable because cb is generally used in damp areas and the joint compound won't hold up. Maybe thinset is the thing? :confused:
  • Sep 1, 2005, 08:48 AM
    labman
    Since cement board usually has tile over it, maybe you just tape it and then apply the tile cement. Getting good advice at stores is an iffy prospect. I let bad weather set in on one of my projects. I asked a Lowe's, and they said they didn't have the antifreeze for concrete. Out in the lot afterwards, another customer approached me and said he was in the business, and always used regular automotive antifreeze. I tried it and it worked fine.
  • Sep 1, 2005, 11:46 PM
    kp2171
    You use glass fiber mesh tape instead of drywall tape because of problems with the alkali in the cement breaking down the drywall tape.

    My understanding is that you do use joint compound with latex polymers.

    But I'm not in the business so I cannot tell you that it'll be a fatal error to skip taping. I've heard that you can skip this, but I cannot find a manufacturer site that says this is OK. I'd tape and level unless I had a pro I trusted say otherwise.

    This link is a pdf file for durock install... looks like manufact. Article... they say to tape and level.

    http://www.usg.com/USG_Marketing_Con...tion_Guide.pdf
  • Sep 2, 2005, 09:17 AM
    ikkyu
    Taping CB Joints
    Thanks for the link- Page 6 has the info I needed- It says to use Type 1 Latex modified mortar to fill joints with 'glass tape. I think the mortar they are referrring to is also known generically as "thinset"- that part I can figure out.
    Many thanks for your generous help and to all who replied :)
  • Sep 19, 2005, 05:13 AM
    dherman1
    Greetings,

    When laying cement backerboard, (Hardipanel, durock, etc) it is important to do the following:

    Apply a supporting bed of dry-set mortar or modified thinset to subfloor.

    Embed the backerboard firmly and evenly in the wet mortar.

    Use the fastener pattern as a guide. Fasten the backerboard with specified nails or screws (as listed in “Materials Required”) every 8" over the entire surface. Keep fasteners 3/8" from sheet edges and 2" in from sheet corners.

    Set fastener heads flush with the surface without overdriving.

    Let this setup overnight.

    Prior to setting the tile, fill all joints with the same mortar used to set the tiles.

    Embed 2" wide high-strength alkali-resistant glass fiber cementitious backer unit tape in the mortar and level.

    To help prevent squeaking, I added another step.

    On top of the subfloor, put down a layer of rosin paper (the red builders paper) and then stapled down a layer of 1/4" underlayment. On top of this, I put the backerboard and followed the steps above.

    In bathrooms, I have added a heated floor using the tile warming mats from Depot. I put down the mats, mix up a batch of self leveling compound and pour that on top of the mats to help set them and protect them.

    Good Luck,
    Dan
  • Jun 16, 2007, 07:02 AM
    Rasluk
    Quote:

    Originally Posted by dherman1
    Greetings,

    When laying cement backerboard, (Hardipanel, durock, etc) it is important to do the following:

    Apply a supporting bed of dry-set mortar or modified thinset to subfloor.

    Embed the backerboard firmly and evenly in the wet mortar.

    Use the fastener pattern as a guide. Fasten the backerboard with specified nails or screws (as listed in “Materials Required”) every 8" over the entire surface. Keep fasteners 3/8" from sheet edges and 2" in from sheet corners.

    Set fastener heads flush with the surface without overdriving.

    Let this setup overnight.

    Prior to setting the tile, fill all joints with the same mortar used to set the tiles.

    Embed 2" wide high-strength alkali-resistant glass fiber cementitious backer unit tape in the mortar and level.

    To help prevent squeaking, I added another step.

    On top of the subfloor, put down a layer of rosin paper (the red builders paper) and then stapled down a layer of 1/4" underlayment. On top of this, I put the backerboard and followed the steps above.

    In bathrooms, I have added a heated floor using the tile warming mats from Depot. I put down the mats, mix up a batch of self leveling compound and pour that on top of the mats to help set them and protect them.

    Good Luck,
    Dan

    The above seems right except for the rosin paper and stapeling of 1/4" underlayment Cement board is primarily used in areas with high moisture like bathrooms and kitchens prior to the installation of tile it is perferred by better contractors over greenboard which is a moisture resistant form of drywall it also costs more. Rosin paper is used between wood floors to prevent squeaking and adding 1/4" underlayment stapled to cement board Well cement board does not take staples very well but it is a excellent underlayment for tile why would you put 1/4 " underlayment over it.

    Check out Reinforcing Concrete

    To answer your original question latex-modified thin-set mortar is used as the joint compound and cement board fiberglass mesh tape for the seems
    Good Luck
  • Jun 16, 2007, 10:05 AM
    glavine
    Use Mesh Tape For Drywall, And Go Over It With Thinset Mortar, It's the Same Stuff You Use To Set The Tile.

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