C33 Surface Preparation for Various Substrates 5 — Questions and Answers
Question 1: A painter is preparing weathered cedar siding that has turned gray. What is the primary purpose of using a wood brightener/cleaner on this surface?
- To kill mold and mildew spores embedded in the wood
- To restore pH balance and open wood fibers for better coating penetration (Correct answer)
- To remove loose paint and mill glaze simultaneously
- To apply a chemical bond coat that replaces primer
Correct answer: To restore pH balance and open wood fibers for better coating penetration
Wood brighteners (typically oxalic acid-based) restore the wood's pH and open the grain after weathering, improving penetration and adhesion of subsequent coatings.
Question 2: When preparing a brick masonry surface that has been coated with silicone-based water repellent, what challenge does the painter face?
- The silicone increases porosity, making the surface absorb too much paint
- Paint will not adhere because silicone repels water-based and most solvent-based coatings (Correct answer)
- The silicone prevents mildew growth and no preparation is needed
- The surface must be heated to 150°F before priming
Correct answer: Paint will not adhere because silicone repels water-based and most solvent-based coatings
Silicone water repellents create a non-porous, low-surface-energy barrier that prevents most paints from adhering, requiring mechanical removal or a specialized bonding primer.
Question 3: According to best practices for the C33 license, what is the purpose of 'feathering' edges when spot-sanding a previously painted surface?
- To create a rough anchor profile for the new coating
- To blend the repair area seamlessly with the surrounding surface to avoid visible edges under the new paint (Correct answer)
- To remove all existing paint from the repair area only
- To apply sanding sealer in a graduated thickness
Correct answer: To blend the repair area seamlessly with the surrounding surface to avoid visible edges under the new paint
Feathering tapers the edges of a sanded or filled repair so it blends smoothly with the surrounding surface, preventing ridge lines from showing through the topcoat.
Question 4: A contractor is repainting a swimming pool deck coated with chlorinated rubber paint. What is a critical compatibility concern during surface preparation?
- Chlorinated rubber coatings must be wet-sanded only to avoid dust
- Solvent-based cleaners can re-dissolve the existing chlorinated rubber film, causing lifting (Correct answer)
- Chlorinated rubber surfaces must be primed with latex before applying any topcoat
- The surface must be neutralized with bleach before sanding
Correct answer: Solvent-based cleaners can re-dissolve the existing chlorinated rubber film, causing lifting
Many solvent-based cleaners and coatings will attack and dissolve existing chlorinated rubber films, causing lifting and wrinkling, so compatibility testing is essential.
Question 5: What does the term 'flash rusting' refer to when preparing steel surfaces, and how is it addressed?
- Rapid rusting that occurs on wet-blasted steel before the primer can be applied, requiring immediate priming or a flash-rust inhibitor (Correct answer)
- Rust that forms only on the surface profile peaks and can be ignored
- A type of rust caused by electrical current and treated with cathodic protection only
- Rust appearing under existing paint that causes blistering
Correct answer: Rapid rusting that occurs on wet-blasted steel before the primer can be applied, requiring immediate priming or a flash-rust inhibitor
Flash rusting is rapid surface oxidation that forms on wet-blasted or water-washed steel within minutes; it is controlled by priming immediately or using a flash-rust inhibitor in the wash water.
Question 6: When preparing a fiberglass substrate (such as a door or boat hull) for painting, which surface preparation step is uniquely critical compared to wood or metal?
- Removing mill scale with phosphoric acid wash
- Sanding to remove the gel coat's mold-release wax and create mechanical adhesion (Correct answer)
- Applying a rust-inhibiting primer coat before sanding
- Heating the surface to open the pores before priming
Correct answer: Sanding to remove the gel coat's mold-release wax and create mechanical adhesion
Fiberglass gel coat contains mold-release agents that prevent adhesion; the surface must be thoroughly sanded to remove the wax layer and create a mechanical profile for the primer.
Question 7: Under California's VOC regulations, which surface preparation activity requires the use of compliant low-VOC or exempt solvents when cleaning substrates before coating?
- Hand sanding of wood substrates
- Solvent wiping of metal to remove oils and contaminants (Correct answer)
- Dry abrasive blasting of concrete
- Pressure washing with plain water
Correct answer: Solvent wiping of metal to remove oils and contaminants
California Air Resources Board (CARB) regulations restrict the VOC content of surface preparation solvents used to clean substrates before coating, requiring compliant or exempt-solvent products.
C33 Surface Preparation for Various Substrates 5
A painter is preparing weathered cedar siding that has turned gray.
What is the primary purpose of using a wood brightener/cleaner on this surface?