Free C33 Identifying and Remedying Paint Failures and Defects Questions and Answers 1 — Questions and Answers
Question 1: A painted surface shows a pattern of deep, interconnected cracks resembling crocodile skin. What is this defect called and what is the most likely cause?
- Chalking, caused by UV exposure.
- Alligatoring, caused by applying a topcoat over an uncured primer. (Correct answer)
- Blistering, caused by moisture trapped beneath the paint.
- Efflorescence, caused by salts leaching from masonry.
Correct answer: Alligatoring, caused by applying a topcoat over an uncured primer.
This defect is known as alligatoring. It typically occurs when a rigid topcoat is applied over a softer or uncured undercoat, causing the top layer to crack as the bottom layer continues to shrink and shift.
Question 2: When painting a concrete block wall, you notice white, powdery salt deposits on the surface. What is the first step to properly remedy this issue before priming?
- Apply an oil-based primer directly over the deposits.
- Pressure wash with a chemical stripper.
- Remove the deposits with a wire brush and rinse the surface. (Correct answer)
- Sand the surface with 80-grit sandpaper.
Correct answer: Remove the deposits with a wire brush and rinse the surface.
This condition is efflorescence, caused by moisture moving through the masonry and depositing salts on the surface. The salts must be physically removed with a wire brush and washed before any sealing or priming can be effective.
Question 3: Paint is peeling in large sheets from a previously glossy interior wall. What is the most probable cause of this failure?
- The wrong type of roller was used.
- The paint was applied in low humidity.
- The previous glossy surface was not sanded or de-glossed. (Correct answer)
- The paint was thinned too much before application.
Correct answer: The previous glossy surface was not sanded or de-glossed.
Glossy surfaces have poor adhesion. Failure to properly de-gloss the surface by sanding or using a chemical de-glosser before painting is a common cause of widespread peeling, as the new paint cannot form a strong mechanical bond.
Question 4: A freshly painted surface develops a rough, wrinkled appearance shortly after application. This defect is known as wrinkling. What is a common cause?
- Applying the paint too thickly. (Correct answer)
- Using a primer from a different manufacturer.
- Painting over a surface that is too cold.
- Not stirring the paint enough before use.
Correct answer: Applying the paint too thickly.
Wrinkling occurs when the top surface of the paint film dries faster than the underlying layer. This is often caused by applying the paint too thickly, painting in direct hot sunlight, or recoating before the previous coat has adequately cured.
Question 5: What is the primary cause of blistering in an exterior paint job?
- Excessive chalking of the previous coat.
- Moisture trapped under the paint film. (Correct answer)
- Using a low-quality paint brush.
- Applying paint in high humidity.
Correct answer: Moisture trapped under the paint film.
Blistering is most often caused by moisture or solvent vapor being trapped beneath the paint film, which then expands due to heat from the sun. This pressure pushes the paint away from the substrate, forming bubbles or blisters. Identifying and resolving the moisture source is critical.
Question 6: After washing an old, painted exterior wall, you wipe your hand across it and a powdery residue comes off. To ensure proper adhesion of the new topcoat, you should:
- Paint directly over the chalky surface with a high-quality latex paint.
- Apply two coats of finish paint instead of one.
- Rinse thoroughly, allow to dry, and apply a chalk-sealing primer. (Correct answer)
- Lightly sand the surface and then apply the finish coat.
Correct answer: Rinse thoroughly, allow to dry, and apply a chalk-sealing primer.
This powdery residue is called chalking, which is the degradation of the old paint binder. This surface must be thoroughly cleaned and then sealed with a primer specifically designed for chalky surfaces to ensure the new paint adheres properly.
Free C33 Identifying and Remedying Paint Failures and Defects Questions and Answers 1
A painted surface shows a pattern of deep, interconnected cracks resembling crocodile skin.
What is this defect called and what is the most likely cause?