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Thread: DUROCK Cement Board for Exterior Walls

  1. #1
    DIY Member MAD King's Avatar
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    Default DUROCK Cement Board for Exterior Walls

    Hello,

    can I use the cement boards for the exterior walls?
    I would like to replace the vinyl siding and the plywood underneath with the cement board.
    I read a little bit that it is possible, but not on how it is done right.
    Anyone with good advices?

    Thank you

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    At least some of the cbu manufacturers (James Hardie for one) make cement based exterior siding...I'm not sure about Durock. On some, you can get it prepainted, or in a primer. Also comes in various styles and panel sizes. Over the years, some of them have had issues, but much of that falls back to not following the instructions to the letter (critical on this type of install).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member MAD King's Avatar
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    Thank you for your reply.
    I know about the cement sidings, but I do not like the look of it.
    That's why I would like to have the cement board and on top some stucco.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I do not think any of the cbu boards are suitable as a structural panel (i.e., say in place of plywood for the cladding)...they are only a compatibility layer for mortar based materials. For wind load, earthquakes, and similar loading, the cbu cannot be used alone - ply, or a similarly rated material must be there to prevent racking and as a resilient panel that holds things together. Cbu would crumble around the fasteners if it were required to be a load bearing panel under those circumstances and then not provide the structural strength required.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member MAD King's Avatar
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    But aren't the panels made from the same material?

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Durock from what little I have seen of it is a crappy board.

    Wonderboard Panels look much better.

    Hardi Backer Panels not approved for outdoors.

    You will want drainage, a rain screen, a scratch coat, a brown coat and a top coat.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    DIY Member MAD King's Avatar
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    Thank you John.

    Looking at Wonderboard and Durock, both look identical:

    http://www.custombuildingproducts.co...x#prodTechDocs

    http://www.usg.com/content/usgcom/en...rdnextgen.html

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    In the trades Dana's Avatar
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    Not all fiber cement backer-boards are rated for exterior use- many will fall apart from freeze/thaw cycles in short years in a Nashville TN climate.

    If you are going for stucco, you need at least a 1/4" ventilation gap (3/4" is better) between the stucco and any sheathing or the moisture drives during the summer will rot your finish wall. If wood sheathing, you'll need a ~0.6-2 perm vapor retarder (double-layered #15 felt is the classic) on the vent-gap side of the sheathing.

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Quote Originally Posted by MAD King View Post
    Thank you John.

    Looking at Wonderboard and Durock, both look identical:

    http://www.custombuildingproducts.co...x#prodTechDocs

    http://www.usg.com/content/usgcom/en...rdnextgen.html
    I worked with both boards this month. Love Wonder Board - hate Durock.

    Found the Durock, dry, brittle and very weak at the surface layer.

    Don't think a cement backer board is your answer.

    Look up Rain Screens and go at the process with a more traditional install.

    Stucc is a funny beast. Lots of variations you can try.

    Do you have a local stucco supply yard? They have many products designed to make life easier for you.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Quote Originally Posted by MAD King View Post
    But aren't the panels made from the same material?
    Fiber cement siding is applied over the structural wall sheathing, it is for appearance and waterproofing, not structural purposes. While an interior wall may add some structural strength, and cbu may be used there, just like drywall, it is not structural from the external viewpoint.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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