CSLB C-33 Painting & DecoratingSurface PreparationHard
A painting contractor is preparing an exterior concrete block wall for painting. The wall is generally clean but has a somewhat rough, porous texture. To achieve a uniform finish and ensure proper paint coverage, what type of primer is most appropriate?
- ABlock filler primer
- BZinsser B-I-N Shellac-Base Primer
- COil-based alkyd primer
- DClear penetrating sealer
Show answer & explanationAnswer & explanation
Correct answer: A. Block filler primer
Concrete block is highly porous and textured. A block filler primer is specifically designed to fill these pores and create a much smoother, uniform, and less absorbent surface. This greatly improves the appearance and coverage of the topcoat, reducing the number of finish coats needed.
Why the other options are wrong
- B. Shellac-based primers are primarily for stain blocking and adhesion on specific substrates, not for filling porous masonry.
- C. Oil-based alkyd primers might adhere but won't effectively fill the deep pores of concrete block, leading to an uneven finish.
- D. Clear penetrating sealers protect but do not fill pores or create a smooth, uniform surface for painting.
Block Filler Primer
A high-build, high-solids primer designed to fill the pores and voids in porous masonry surfaces like concrete block, creating a smoother finish.
- Essential for uniform topcoat appearance.
- Reduces paint consumption on porous substrates.
- Applied thickly to fill texture.
Memory trick: Porous blocks need 'filling' to make them smooth and strong.