Backerboard first then sheet rock?


Old 04-19-05, 06:15 AM
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Question Backerboard first then sheet rock?

We've completely gutted our bathroom and are in the process of putting it back together. Our old walls were tiled and the floor had tiling over cement (from the 60s). Do we put our backerboard down on the floor before we sheet rock or after?

In other words, does the sheetrock go all the way to the subfloor or on top of the backerboard?

We're tiling over the floor and will have wainscotting on the bottom part of the walls (with baseboard).

Thanks in advance!
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Old 04-19-05, 11:26 AM
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I'd suggest you install the backerboard first. Then cover it with plastic to keep it clean. Install your vapor barrier then hang the drywall next, and there's no reason it needs to be tight against the floor. Generally drywall hangers will leave a 1/4 to 1/2" gap at the bottom of the drywall, because they are most concerned with lifting the drywall up against the ceiling tight with a kick jack.
Old 04-20-05, 08:41 AM
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My concern is the condition and make up of your current subfloor. Post back before you begin to install backer to make sure you don't have any other requirements to use the backer. You cannot apply backer directly to plank or single layer non t-g ply subfloor, and there are specific requirements as to which ply to use, grading, rateing and thickness. Anyway, I'd install the sheetrock first and get it taped and primed before installing the backer, but any extra ply you might need can be done before the walls go up.
Old 04-21-05, 02:33 AM
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Thanks for the tips. I just wasn't sure how far down to sheet rock. Hopefully we'll get that finished this weekend, then on to the floor.
Old 04-21-05, 04:02 AM
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An improper floor prep will cause you tremendous aggrevation. So here's the deal. If you have an older home with plank subfloor, you will need to add 1/2" of bc graded exterior rated ply before you install the cement board which gets set into a bed of unmodified thinset. You do not want to use any premixed products on your floor either. If you have plywood subflooring and it is not t-g ply then you will need to add a minimum of 3/8" bc or better exterior ply before installing backer. If you have your old mortar bed still in place, you cannot install backer over it. Any cracks in the mortar bed need to be filled and then an antifracture membrane installed or the cracks will transfer through the tile. The requirements for plywood are as follows-all plywood must be exterior glued ply, rated fro underlayment use. Plys are graded with 2 letters, A thru D. No plywood with a D in the grading or listed as "sheathing rated" can be under the ceramic floor. Technically, the lowest grade of plywood you could use would be CC plugged, but only lumber yards will have that. BC exterior should be available at any big box. No layer of plywood can be less than 3/8" thick. Any thinner grades are too unstable under ceramic. The orientation of the ply would be face grain perpendicular to the joists. OVerlap any seams in the lower level by atleast 1'. End the layer so that it extends 4" past the joists. There needs to be a gap of 1/4" around the perimeter and 1/8" between sheets. Screw each layer beyond the subfloor down only to the subfloor, never to the joists every 6-8" over the entire face of each board and do not use glue between layers of ply. Good luck with your project.

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