In the course of restoring several old homes I’ve come across a solution for filling cracks in sound plaster in lieu of removing for complete replacement. First, correct any structural problems that may have led to cracks or separations. Second, channel out the cracks with a church key or similar tool to a depth of at least 1/8 in., then fill the cracks with a quick-setting, non-shrinking drywall compound (i.e., Durabond by U.S.G.) or a lime putty. After it dries, tape the cracks with plasterer’s fiberglass mesh and all-purpose drywall compound. Then float the entire surface with one or two coats of drywall compound, using a trowel or wide knife. Sand out when dry and prep for finish. Large areas of new plaster can be blended with old in the same manner.
Alan Berkowitz, Kansas City, MO