Leveling drywall patch

Due to a problem with my furnace, I recently had a lot of moisture get behind a wall and of course, mold to follow. All said and done I will need roughly 3 4x8 sheets to replace the damaged drywall.

My problem is they appear to have used 2 3/8" sheets stacked on one another, making it 3/4" total. All I can find around here is 5/8" boards. So, I need to make up a 1/16" difference. My friend suggested just mudding out the difference, but there is some large, older molding on the ceiling that i need to marry up to that makes that seem really difficult.

My thought was corrugated cardboard. But I saw this post and it didn't give a sure answer on whether or not that would be ok.

It mentions the cardboard giving too much and cracking the joints right away, but as I see it, the cardboard is thicker than what I need, so once it is compressed, it's not going anywhere. Any thoughts on what I should do?

• Since you'll be taking the molding down to replace the drywall, doesn't it just make sense to re-trim the room and cope as needed? Aug 6, 2015 at 13:49
• FYI, your math is a little off. 3/4 - 5/8 = 1/8, not 1/16 Aug 6, 2015 at 20:19

Why not use standard 1/2" drywall after you shim out the studs. Use 1/4" stock or rip 1 1/2" strips of 1/4" plywood. Tack these to each stud. Then screw the 1/2" drywall through the shims and into the studs. I would probably use 1 5/8" drywall screws for a better grip.

By the way, if this is in or near a furnace room, be sure to use fire rated drywall.

• Great suggestion. Beat me to it. Aug 6, 2015 at 13:49
• +1 I like this suggestion if the 1/2" is used. If 5/8" type X is used, then I think you're looking at a lot of mud instead of attempting a 1/16" shim.
– BMitch
Aug 6, 2015 at 14:09
• You could also do the 1/2" drywall & 1/4" drywall to make the 3/4" needed. Then really nothing would change. You'll just have to be careful that the end bevels don't match up since that would be good cracking/bending opportunities. Aug 6, 2015 at 14:17
• I think this sounds like the best way to go. Thanks for your time.
– Nick
Aug 6, 2015 at 14:37

You may want the type X 5/8" drywall with the furnace there (may not be required but it won't hurt). When you use a large mudding knife, the 1/16" over a 8-12" span will be difficult to impossible to detect. If you can pull the ceiling moulding without damaging it, I'd do that first. Replace the drywall behind the moulding, mud and tape the entire patch area, prime the wall, reinstall the moulding, and paint.

• Sorry, I worded that poorly. The furnace is in the room below, the exhaust was running up through the wall, out the chimney, causing condensation. Got a new high eff. furnace that exhausts directly through the basement wall now.
– Nick
Aug 6, 2015 at 14:11
• In that case, I like blb's suggestion best. Shim out the wall 1/4" strips of wood and install 1/2" drywall over top. It will have the best resulting appearance.
– BMitch
Aug 6, 2015 at 14:17

They make 1/16" Drywall shims, you can find them at home depot, Drywall suppliers have 1/8" drywall shims. They are made of cardboard, and do the job nicely.