Q:
I’m replacing 3 ft. of drywall along the bottom of an existing wall. The drywall above is in good condition and is painted with satin latex paint. Do I need to do anything special when taping this joint?
Elizabeth Smith, Pittsfield, VT
A:
Myron R. Ferguson, author of the book Drywall (The Taunton Press, 2008), replies: This question can be asked whenever a drywall repair is necessary. First, the painted surface should be clean. If the paint has a sheen to it, I usually scuff the surface with 80-grit or coarser sandpaper. I may even apply some compound to a test area.
I prefer heavyweight drying-type compound to embed tape and a midweight or lightweight drying-type compound for finish coats. I’ve found that faster-setting compounds don’t adhere as well, and they always require that you sand the surface first.
If you are concerned about adhesion, you can use a compound additive like Strait-Flex Super Bond or Trim-Tex Mud Max. They are mixed into the compound to add strength and increase the bond. I also have used plaster-bonding agents on projects where I have concerns. The plaster-bonding agent is brushed or rolled on the surface, not mixed with the compound.
Whenever I tape over a painted surface, I get air bubbles in the compound. I think this happens because there is little absorption into the surface. Whatever the reason, you have to wait until the compound dries and either scrape or sand off the bubbles and apply another coat.
Another potential problem is that the area that you tape might be smoother than the rest of the wall or ceiling, where there is typically a slight texture from the paint roller. This may show up after the surface has been primed and painted. The best solution is to apply a very thin coat of compound to the entire area. Lightweight drying compound, lightly sanded when dry, will work fine.
