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Backstory: We had a leak in our roof that damaged some of the ceiling drywall. When we put new drywall up, the pre-existing drywall "sagged" a bit lower than the fresh piece that was screwed into the ceiling joists. Because of this, I layered the joint compound so that the two would be as level as possible.

In the latest coat of joint compound, the compound is showing small cracks that I assume happen while it is drying (and shrinking?).

  • I've read elsewhere not to use sandpaper but some sort of sanding sponge. Confirm or Deny?
  • Do I need to use a different product to fill these gaps?
  • Would this be caused by too thick of a coat of joint compound?
  • What is the best way to build it up so that next time I can do this right?
Niall C.
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rynmrtn
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1 Answers1

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Firstly, @Michael Karas answer addresses the "sagging"

Cracking: Premixed Joint Compound (JC) hardens by drying out. As such, it tends to shrink. I only use it for final top coats, where the shrinkage is mitigated and application layers are about 1/8 or so.

Setting JC is dry and mixed with water to a similar consistency as Premixed JC, but it hardens chemically (due to plaster of paris). It shrinks much less.

If your patch is dry and firm, you can continue to overcoat it with premix until you obtain a flat surface.

If it is not firm, remove offending parts until you have a firm base. Replace with setting JC, adding fiberglass mesh tape or other backing as needed. Bare JC shouldn't span more than 3/4 inch without a mechanical backing: Refer to Jon Raynors answer here

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HerrBag
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