Expert: Richard Taylor, AIA - 5/29/2006

Question
Hi Richard,
I have to replaster a room that a drywall worker did for me.  He primed the room after he plastered.  Is it OK to apply plaster right over the primed paint once it is dry?  Also do you recommend the "light weight joint compound" over the "all purpose joint compound"?  

Also:
What is the recommended screw lenth for half inch drywall on ceilings?

The plaster guy also left bubbles in the tape.  Do you know how I can fix that?

Any other drywall tips to leave the wall looking smooth would be greatly appreciated.

Thanks a million in advance.  I learned my lesson in hiring the wrong workers.

Carl Bernstein

Answer
Good Morning Carl - thanks for your questions!

All your questions are about drywall except one that's about plastering.  They're two very different things.  But even if you're applying new joint compound over some painted areas the comments below still apply.

Generally, you can't plaster over paint.  This is especially true for oil-based paints, but plastering over latex isn't ideal either.  The problem is that you've lost the mechanical adhesion between the layers of plaster - all that would be holding the final skim coat on is paint (not good!).  Check with your paint store to see if they have a product to prepare a painted wall for plaster.

Personally, I prefer regular joint compound over the lightweight.  It's a little easier to work and to finish.

One inch screws are adequate for ceilings.

Tape bubbles must be completely cut out and redone.

The details of the whole process of hanging and finishing drywall properly are beyond the scope of this forum, but there are a couple of important keys:

1) good, straight framing.  No amount of mud will make up for poor framing
2) proper alignment and sizing of boards to minimize joints
3) glue AND screw to the framing
4) apply just enough mud to seat the tape, no more
5) quickly feather the top coat to minimize sanding (takes some skill)
6) use yellow mud for the finish coat

Or, find a skilled crew and save yourself a lot of time and headaches!

Hope this helps!

Richard Taylor, AIA
Richard Taylor Architects, LLC
www.rtastudio.com
www.betterhouseplans.blogspot.com