What is the main substrate preparation for plastering over masonry?

What is the main substrate preparation for plastering over masonry?

• A. Clean surface, remove loose material, dampen to limit suction, and ensure sound substrate
• B. Apply primer and sealant
• C. Paint the surface
• D. Sand until smooth

Answer: (A)

The essential idea is to present a clean, sound masonry surface with controlled suction so the plaster can bond properly. Start by removing all loose or flaking material, dirt, and any efflorescence or contaminants. A clean, stable base gives the plaster something solid to grip and reduces the chance of failures at the first layer. If the masonry is very porous, dampen it slightly before applying plaster. This reduces suction, so the plaster doesn’t pull water away from the mix too quickly, which can cause early shrinkage cracks or a weak bond. At the same time, ensure any cracks or damaged areas are repaired so the substrate remains mechanically sound and won’t deform under the plaster. Primer or sealant can be used in some situations to improve adhesion, but they’re not the core substrate preparation for plastering over masonry. Painting the surface isn’t relevant to the prep, and sanding the masonry isn’t typically the proper step for preparing a masonry base for plaster.

The essential idea is to present a clean, sound masonry surface with controlled suction so the plaster can bond properly. Start by removing all loose or flaking material, dirt, and any efflorescence or contaminants. A clean, stable base gives the plaster something solid to grip and reduces the chance of failures at the first layer.

If the masonry is very porous, dampen it slightly before applying plaster. This reduces suction, so the plaster doesn’t pull water away from the mix too quickly, which can cause early shrinkage cracks or a weak bond. At the same time, ensure any cracks or damaged areas are repaired so the substrate remains mechanically sound and won’t deform under the plaster.

Primer or sealant can be used in some situations to improve adhesion, but they’re not the core substrate preparation for plastering over masonry. Painting the surface isn’t relevant to the prep, and sanding the masonry isn’t typically the proper step for preparing a masonry base for plaster.