CSLB C-33 Painting & Decorating

B. The first coat is too thick, and the second coat is too thin, requiring remediation.

While the total DFT (10+5=15 mils) falls within the 12-16 mil range, individual coat thickness specifications are crucial for multi-coat systems. Applying a coat too thick can lead to solvent entrapment, cracking, or poor intercoat adhesion, while applying it too thin compromises protection. Both coats must meet their individual specified ranges.

C. An oil-based or shellac-based stain-blocking primer.

Cedar and other 'bleeding' woods contain tannins that can migrate through water-based primers and topcoats, causing discoloration. Oil-based or shellac-based primers are effective stain blockers that seal in these tannins.

A. Oil-based alkyd primer

Oil-based (alkyd) primers are highly effective at blocking water stains, smoke stains, and tannins due to their superior sealing properties. While some specific water-based stain-blocking primers exist, a general oil-based primer is usually the go-to for severe stain blocking.

B. The primer was applied in an area with insufficient air circulation, hindering solvent evaporation.

Proper air circulation is crucial for the drying and curing of solvent-based coatings like oil-based primers, as it helps carry away evaporating solvents. Insufficient circulation will significantly prolong drying time and can leave the surface tacky.

D. Lightweight spackling compound

Lightweight spackling compound is specifically designed for filling small holes, cracks, and imperfections in interior surfaces like gypsum board. It dries quickly and sands easily, making it ideal for preparation before painting.

D. Acid etching to achieve a CSP 2-3 profile.

For new concrete floors receiving an epoxy coating, achieving a proper surface profile (typically CSP 2-3) is critical for mechanical adhesion. Acid etching (or grinding/shot blasting) creates this profile by opening the concrete's pores. Plain power washing cleans but doesn't profile. Densifiers and curing compounds alter the surface chemistry in ways that can hinder, rather than help, epoxy adhesion if not properly removed.

C. Air entrapment or outgassing from the porous concrete substrate

The description of small, circular craters extending to the substrate, especially on a concrete floor, is characteristic of 'pinholing' or 'cratering' caused by air entrapment within the porous concrete or outgassing from the substrate as the coating cures. Concrete is notorious for this issue.

B. 0.5 gallons

The mixing ratio is 4 parts Base (A) to 1 part Hardener (B). If there are 2 gallons of Base (A), divide the amount of Base by 4 to find the required amount of Hardener: 2 gallons / 4 = 0.5 gallons of Hardener (B).

C. The coating will not achieve its full chemical resistance or hardness.

Induction time (or 'sweat-in time') is a critical waiting period after mixing two-component coatings. It allows the chemical reaction between the components to properly initiate and for the mixed material to achieve its intended properties (e.g., viscosity, wetting, and most importantly, full cross-linking potential). Skipping or reducing this time means the chemical reaction is not fully underway, leading to a coating that may not achieve its specified hardness, chemical resistance, or other performance characteristics, compromising its long-term durability.

A. Mix smaller batches and work more quickly, as elevated temperatures will significantly reduce pot life.

Elevated temperatures accelerate chemical reactions, including the curing of epoxy coatings. This will significantly reduce the pot life, necessitating smaller batches and faster application to avoid the material curing in the pot. Adding more hardener or solvent will negatively impact the coating's properties.

D. Dry spray / Overspray

Dry spray or overspray occurs when atomized paint particles dry in the air before reaching the substrate or a wet film. This results in a rough, textured, dull finish because the dried particles do not coalesce properly. It's common with fast-drying, solvent-borne coatings and improper spray technique.

B. Increase the spray pressure to achieve better atomization.

A spray pattern with 'fingers' or 'tails' (heavier edges, lighter center) indicates poor atomization. This generally means the pressure is too low for the viscosity of the material being sprayed. Increasing the spray pressure will force the material through the tip more effectively, leading to better atomization and a more uniform fan pattern.

A. Zinc-rich primer.

New galvanized metal requires a specialized primer, typically a zinc-rich primer or a specific DTM (Direct-to-Metal) acrylic primer designed for galvanized surfaces. The zinc reacts with the zinc coating on the galvanized metal, providing excellent adhesion and corrosion protection. Standard oil-based primers can react with the zinc, leading to poor adhesion and peeling, while standard latex and shellac primers lack the necessary properties for this substrate.

D. 14.0 - 17.5 mils

To calculate the DFT, multiply the WFT by the solids by volume percentage. For the lower end: 20 mils * 0.70 = 14.0 mils. For the upper end: 25 mils * 0.70 = 17.5 mils. Therefore, the expected DFT range is 14.0 - 17.5 mils.

C. Wood putty

Wood putty is specifically designed for filling small holes, dents, and imperfections in wood surfaces. It dries hard, can be sanded smooth, and accepts paint well.

D. Spackling compound.

Spackling compound is specifically designed for filling small holes, cracks, and imperfections in plaster, drywall, and wood. It dries quickly, sands smoothly, and accepts paint well.

A. Applying the epoxy over a porous concrete surface that was not adequately sealed or outgassing.

Pinholing on concrete is most commonly caused by outgassing from the porous substrate. As the epoxy begins to cure, air or moisture vapor trapped in the concrete pores tries to escape, bubbling through the wet film and leaving small craters. This is especially prevalent with high-solids coatings that dry quickly at the surface.

B. Conduct a surface profile test to verify the CSP level meets specifications.

After mechanical preparation like grinding, it is critical to verify that the achieved surface profile (roughness) meets the coating manufacturer's specifications. A CSP (Concrete Surface Profile) test, often using comparator chips, is the standard method for this. An insufficient profile will lead to poor mechanical adhesion, while an excessive profile can require more material or lead to pinholing. Verification ensures the substrate is ready for coating.

B. Lightly scuff sanding the entire surface.

New PVC trim often has a smooth, glossy surface that paint struggles to adhere to. Lightly scuff sanding creates a mechanical 'tooth' for the paint to grip, which is critical for long-term adhesion. While some DTM primers claim to adhere without sanding, scuff sanding is still the most reliable and critical step for smooth, glossy plastics like PVC.

D. Acid etching or mechanical abrasion to create a profile

Epoxy coatings require a profiled surface for mechanical adhesion. A smooth, troweled concrete finish lacks the necessary profile. Acid etching (for smaller areas) or mechanical abrasion (grinding/shot blasting) creates the required Concrete Surface Profile (CSP) for proper epoxy bond.

D. Sand all joint compounds and patched areas smooth.

After taping and mudding, joint compound must be sanded perfectly smooth to eliminate ridges, bumps, and tool marks, which would otherwise be visible through the final paint coats and compromise uniformity.

D. 12.5 mils

To calculate WFT from DFT and % Solids by Volume, use the formula: WFT = DFT / (% Solids by Volume). In this case, WFT = 10 mils / 0.80 = 12.5 mils. The coverage rate (160 sq ft/gal) is extraneous information for calculating WFT from DFT.

D. Scrape away all loose and peeling paint, then feather-edge the remaining paint.

Before applying any new coatings, all loose and failing existing paint must be removed to ensure proper adhesion of the new paint. Feather-edging creates a smooth transition.

C. Tri-sodium phosphate (TSP) substitute

Tri-sodium phosphate (TSP) or its substitutes are highly effective degreasers and are specifically recommended for cleaning surfaces contaminated with heavy grease and nicotine, ensuring proper adhesion of subsequent coatings.

D. Wash the wall thoroughly with a wallpaper adhesive remover solution.

Wallpaper adhesive residue must be completely removed before priming and painting. Washing the wall with a wallpaper adhesive remover solution dissolves and loosens the remaining glue, allowing it to be wiped clean. Failing to remove it can lead to primer/paint adhesion failure, bubbling, or an uneven finish.