General Contractor Practice Exam

How should a masonry wall be prepared prior to applying plaster?

1. Dry and clean

2. Moisten with water

3. Scrub with detergent

4. Apply a primer

The correct answer is: Moisten with water

Preparing a masonry wall before applying plaster is crucial for ensuring the best bond and finish quality. Moisten the wall with water helps to prevent the plaster from drying out too quickly, which can lead to cracks and poor adhesion. This step is particularly important because dry masonry can absorb moisture from the plaster, creating a situation where the plaster sets too fast and does not adhere properly to the wall surface. By moistening the masonry, the wall remains slightly damp, which allows the plaster to cure at a controlled rate, promoting better bonding and overall performance. This practice is especially relevant for new masonry or very porous surfaces that might otherwise draw moisture away too rapidly from the plaster mix. In contrast, simply having a dry and clean surface, while beneficial, does not address the need for moisture during the curing process. Scrubbing the wall with detergent or applying a primer could potentially introduce issues, such as residue left on the surface or an improper bonding layer, both of which would negatively affect the plaster application. Hence, moistening the masonry is the most appropriate and effective preparation method prior to plastering.