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For outdoor kitchen, do I need to use plywood on top of the framing, then cement board? Or can I put cement board directly mounting to the frame like this?

enter image description here

Source: http://www.homedit.com/how-to-build-outdoor-kitchen-cabinets/

The reason I am asking because cement board doesn't seem that strong to hold. It might crack. But I also rather not to use plywood and THEN cement board because that makes it too thick.

  • Have you looked at paperless gypsum board products (i.e. paperless drywall, glass-faced gypsum board)? – ThreePhaseEel Aug 21 '16 at 3:47
  • I have never heard of them. What's the benefits? Are they outdoor? – HP. Aug 21 '16 at 5:41
  • They are indeed outdoor-rated -- think "drywall that shrugs at getting wet" – ThreePhaseEel Aug 21 '16 at 13:56
  • So this drywall would replace cement board + plywood for outdoor tile / stone project? Well, my goal is to make it as thin as possible due to my mistake. I only leave 0.5" between outer side of the frame and the edge of the granite countertop. Meaning if it's too thick below, it will extrude outside of the granite surface, which is ugly. – HP. Aug 22 '16 at 0:34
  • Have you considered framing it with steel instead of wood? Then your movement concern diminishes. – Matthew Mar 15 at 4:07
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The purpose of 3/4 inch plywood under the cement board is to keep the counter from flexing enough to crack mortar/thinset or tiles.

If there is adequate bracing under the cement board—like 2x4s on edge at 12 inch spacing—and press with 150+ pounds at any point and not have perceptible flexing, I think you are good to go.

  • I am planning to do cement board on the vertical surface only. Since there is no weight, I assume it's OK? The only risk is the expand and contract of lumber and the weight of the tiles or stone veneer I'm gonna put on – HP. Aug 21 '16 at 5:40
  • @HP.: What about things resting against it? People, tables, pets, etc. – wallyk Aug 21 '16 at 5:44
  • Also as mentioned, expansion and contraction of the lumber, this will cause the concrete board to warp over time, eventually working off the tiles you set (assuming you get snow or high humidity). – Chris Aug 21 '16 at 13:12
  • I have done many showers and tub surrounds with only 1/2" cement board and every type of tile from 2" to 12" with no problems. I used to use green board (the water resistant Sheetrock) but have found for tile cement board holds up better. – Ed Beal Aug 21 '16 at 14:21
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    @EdBeal Well from the photo, isn't what they use 0.5" cement board? I guess it's acceptable vs. using 0.5" plywood + 0.25" cement board, right? – HP. Aug 22 '16 at 0:35
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For a vertical application movement is a bigger concern that weight carrying ability. If the cement board is framed well (studs every foot) with no load I think it would be fine.

For what it's worth:

  • I did a woodstove surround on 1/2" drywall spaced from the surrounding wall by 1/2" using 1" wide scraps of drywall every 8 inches. used mastic and 1/4" tile. No problems.
  • Later did a kitchen wall/backspash using tile, mastic on 1/2" oriented strand board, textured side out. No problems.

I'm not sure in this application if you need even backer board. I'd be tempted to make a frame that would hold the granite slab in location, with some bottom support, and keep it from tipping out with a bead of silicon at the top.

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