01/05
NWCB Technical Document
INTERIOR PLASTER
700-103
Patch Repair on Painted Interior
Gypsum Plaster
One of the strongest selling points for gypsum plaster is the abuse resistance and long service life of gypsum plaster. Because of the long service life, it is not uncommon to find older interior plaster walls and ceilings with multiple
layers of paint coatings. When repair or patchwork is required for these surfaces, this can present a challenge to
contractors.
The first concern for the contractor is the bond of the paint coatings to the plaster or the subsequent paint coatings.
As layers of paint are added over the years, each layer places stress on the underlying layers. In addition, the underlying coats will continue to age and may become hard and brittle.
Paint should be removed if there is:
• Checking
• Chalking
• Blistering
• Alligatoring
• Cracking
• Delamination
• Excessive layers
Of these conditions, the one that is least obvious is the excessive layers of paint. Excessive layers of paint can
appear intact and adequately adhered to the substrate prior to repainting. The most common problems when more
materials are applied are lifting, blistering and peeling and delamination. The problem is rarely between the new
plaster and the newest layer of paint and more often in an underlying layer of paint. The cause may be the weight of
the new plaster or the curing process, in either case it is a form of stress that has pushed the older coating bonding
to its ultimate failure point.
Removal of the paint (excessive layers) is the best option for the most secure bond of new plaster. If removal is not
possible, a test patch with a bonding agent should be done to insure adequate bond of the underlying layers.
For plaster patching, follow NWCB Technical Document 700-102 Patching Interior Lath and Plaster.
This technical document is to serve as a guideline and it is not intended for any specific construction projects. NWCB makes no express or implied warranty or guarantee of the
techniques, construction methods or materials identified herein.
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