Patching and Plastering - Mystery Wall Material- How To Fix Cracks?

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bunsorama
10-24-09, 11:40 PM
My house was built around 1950 and the walls and ceilings have serious crackage going on. I cut a piece out to install a new light switch, and have posted below a pic of the cross section. I would like to know what I'm dealing with before I attempt to fix the cracks. I have heard that plaster is very hard to sand, but whatever the skim coat is on this material, it is soft like joint compond. And unlike gypsum board, drywall, sheetrock... the entire surface of the walls and ceilings have been skim coated. Just like plaster over lath.


The first 3/8" thick layer is very hard to cut. It appears to be imbedded with sand or super fine crushed rock.

The second layer looks like gypsum board.



http://i53.photobucket.com/albums/g62/mithslew/MYOLDHOUSE-PLASTERWALLS.jpg

marksr
10-25-09, 05:59 AM
As you found out in another thread, you have plaster with a gypsum [drywall] lath.

Most of us that don't do plaster for a living will use a setting compound like durabond to patch plaster. I'd scratch out the cracks, make sure they aren't dusty and fill with durabond. One of the plaster pros should be along later with more info for you.
mgmine
11-03-09, 09:26 AM
The only way to rid yourself of the cracks is to tape them using drywall compound. You will need to first use a 6" knife then a 12" just as if you were doing a drywall seam. I you simple try to fill the cracks they will reappear and you won't be any better off.