cbu over drywall/greenboard [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-29-2003, 09:03 AM
Rob Z:

I have one customer who insists on us affixing a 5/16" pc of cbu on top of his ready to go greenboard in standard tub surrounds. This is done in an effort to achieve a "mudded" look; we finish the sides and top (run to standard height) with A-4200s. (The baths are always 4x4/6x6). For a variety of reasons I remain uncomfortable doing this. However, our approach so far has been this (no problems by the way in over 50 tub surrounds done over the last 2+ years): We "laminate" the CBU w/ 118.4 thinset, using proper screws. We then silicone (very heavy) the tops and bottom before setting the tile. (You may be able to infer that moisture is my biggest fear--that and gravity!) Rob, should i be doing anything differently? We then set the tile in 118.4 also. Maybe some sort of moisture barrier? 118.1 thinset to affix the board? Your thoughts would be appreciated. As a final note, the quality of framing is usually excellent. Thanks, Jim.

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Bud Cline
01-29-2003, 06:47 PM
That procedure has been used for decades...what's wrong with that?:) It's done in Texas all the time.

01-29-2003, 07:00 PM
No problems with using the CBU. Heck, it's better than greenboard !!

I add a layer of roofing felt between the greenboard and CBU as a vapor barrier


John Bridge
01-29-2003, 07:13 PM
Hi Jim,

You might have to email Rob. He's in over his ears right now. ;)

Nail the CBU over the greenboard with a moisture/vapor barrier in between the two. Forget laminating it. Use the 1/2 in. product and the A-4200 will work out perfect.