PLASTER special subjects The bursts are conical fragments that show up on the surface of the plaster leaving holes which vary in size. They are caused by impurities in the mixture which react with moisture, burst, and create cavities within the plaster. Once the cause of the bursting is removed, the hole can be filled with a sealant (elastomeric or another type) and then paint the surface. The detachment of the plaster is often perceived by the hollow sound you hear when the surface is gently tapped. The plaster tends to bulge and detach from the wall, because the exterior part of the wall (that is exposed to the elements), shrinks at a different rate from the part of the plaster in contact with the wall. This is especially true for excessively thick layers of plaster. Small areas of detachment are not important, but larger areas must be removed and replaced. Since plaster detachment is generally the result of poor substrate preparation, it is important to make sure that the bond between the plaster and the wall is as strong as possible. That can be achieved by: • Thorough cleaning of the dust that has settled or the oily pollutants that might be on the surfaces. • Using liquid bonding agents (resins) following the manufacturer’s instructions and procedures • Apply a scratch coat before plastering with regular or one-coat plaster. BURSTING DETACHMENTS Repair & Renovation Guide 67
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