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We have a dry basement with a concrete floor. When putting on the wall boards, how much (if any) gap should there be between the concrete floor and the bottom of the board? The boards are 3/8 inch, I was thinking about using a scrap piece drywall on the ground and then resting the board on top of it while installing, and then pulling it out when finished.

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Our walls were a bit taller than 8' so I just leveraged them to meet the ceiling, and whatever gap was at the bottom was covered with trim. As long as the sheetrock isn't touching the concrete, you should be fine. – DA01 Dec 7 '11 at 20:36
up vote 21 down vote accepted

Drywall should definitely not touch concrete as moisture will wick (ie flow up the surface as in a candle/lamp wick) into the drywall and encourage mold growth.

3/8" should be sufficient - your prop up plan is not only appropriate, but a common technique used by drywallers.

enter image description here

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1/2" give or take is fine, just be sure there's no direct contact that can wick up moisture. The trim will cover any gaps, so it's not critical that these are even.

Note that drywall on the wall should support the ceiling drywall, meaning you install the ceiling first, and the wall is installed tight against the ceiling. For the bottom piece, you use a roll lifter under the drywall to lift it up and give you a tight fit to the board above it. You rest the drywall on the small lip on the end of this lifter and then step on the other side as a lever to raise it up.

drywall roll lifter

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Good point on the drywall supporting the ceiling first – Steven Dec 7 '11 at 20:09

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