Primers, Specialty Coatings, Sundries, and VOC Rules
This chapter completes the products content area. It covers what a primer is actually for and which primer belongs on which substrate, the specialty coatings a California painting contractor is regularly asked to specify, the brushes, rollers, tapes, and sealants that are collectively the sundries line in an estimate, and California's air-district-based VOC regulation, which is stricter and structured differently from the federal system most trade material describes.
What a Primer Does
A primer's job is to seal the surface and promote adhesion, and different primers emphasize different halves of that job. On new, unpainted drywall, the primary purpose of a primer or sealer is to equalize porosity so the finish coat dries to a uniform sheen; paper facing and joint compound absorb at very different rates, and without a sealer the compound joints read as dull patches under raking light. That is the mechanism behind the most common interior complaint there is: a wall with several skim-coated repairs that looks blotchy in the finish even though the whole wall was primed, because the primer itself was absorbed unevenly and did not seal evenly. On bare ferrous metal, the primer's job is corrosion protection, which requires a rust-inhibitive metal primer rather than a general-purpose product. On a glossy previously coated surface, a bonding primer is formulated specifically to grip slick, low-porosity substrates and hold the topcoat, which an ordinary primer will not do. On a chalky exterior wall that has been washed but still shows light chalk, a penetrating conditioning primer binds the residual chalk to the substrate so the topcoat has something solid underneath. On weathered but sound siding, an oil or alkyd penetrating exterior wood primer soaks into the loosened surface. And on a wall about to receive wallcovering, a wallcovering primer seals the wall so that the covering can be removed later without destroying the drywall facing. In each case the substrate, not habit, chooses the primer.
Specialty Coatings You Will Be Asked to Specify
An elastomeric coating is a high-build, flexible film used to bridge and waterproof hairline cracks on exterior stucco, and it only performs as intended when it is applied at the film thickness the manufacturer specifies, because its crack-bridging ability is a function of film build. Applied too heavily in one pass it mud cracks, drying with a network of wide cracks; applied too thin it behaves like ordinary paint and the crack reappears. It is a wall product, not a deck product: wall elastomerics are not formulated for foot traffic or standing water, so they do not belong on a flat concrete patio. A masonry water repellent is a different tool for a different job. It repels liquid water while remaining vapor permeable, so the wall can still dry outward, which is why it is specified on a brick facade where a paint film would trap moisture. For a redwood deck whose owner is tired of a film peeling every two years, the honest recommendation is a penetrating stain that wears away gradually rather than a film-forming coating that peels. Several products exist for particular building problems: an anti-graffiti coating may be sacrificial, meaning the coating comes off with the graffiti and is reapplied, or permanent, and the owner needs to know which they bought; a dry-fall coating is formulated to dry into a removable powder before it lands, which is what lets an open warehouse ceiling and its exposed structure be sprayed without masking everything below; and a coating with a mildewcide in a tighter, higher-sheen film is the right answer for a shaded north-facing wall that grows mildew within a year of every repaint, which is also why California hillside exteriors often specify a mildewcide even in a dry climate, because shaded and irrigated walls stay damp enough for growth.
Sundries: Brushes, Rollers, Abrasives, Tapes, and Fillers
Sundries are the tape, plastic, caulk, sandpaper, brushes, and rollers that an estimator carries as a percentage of material cost, and choosing them correctly is a technical decision. Brush filament follows the coating: natural bristle, traditionally china bristle, is preferred for solvent-borne alkyd enamels, while nylon and polyester blends are used for waterborne coatings because they keep their stiffness in water where natural bristle goes limp and loses its shape. Roller covers follow the surface: a short nap of about a quarter inch suits smooth surfaces such as new drywall and fine finishes, while a long nap of three-quarters to one and a quarter inches is needed to reach into rough stucco. Natural lambswool or mohair is the traditional cover material for solvent-borne alkyd enamels. Every new roller cover is pre-wet and de-linted before it is loaded, or the first wall of an enamel job carries lint into the film. Abrasives follow the material: an open-coat aluminum oxide paper has spaced grain that resists clogging with soft paint residue, and drywall finishers use an abrasive screen or a sanding sponge rather than paper on joint compound because those resist loading and conform to the surface. Progressing through grits works because each finer grit removes the scratches the previous grit left. Masking follows the schedule: a low-tack delicate-surface tape is used against a wall finish-coated four days ago, and exterior masking plastic left up through a week of hot sun will build heat and bake the adhesive on, making removal difficult. Canvas drop cloths are preferred over thin plastic on interior floors because canvas absorbs drips and stays flat underfoot rather than becoming a slick, sliding hazard. Fillers and sealants follow the joint: a paintable polyurethane sealant belongs at a moving joint between a stucco wall and a metal door frame, setting-type joint compound suits a same-day interior repair, and an epoxy consolidant followed by an epoxy filler is what preserves a rotted section of a decorative exterior column the owner wants kept rather than replaced.
Wallcoverings, Clear Finishes, and Stains
The C-33 classification covers papers and fabrics as well as paint, and the exam reflects that. Commercial vinyl wallcovering is graded by type, and Type II designates a medium-duty weight suited to normal commercial wall traffic, which is what a busy corridor typically specifies. Adhesive selection follows the substrate: a clay-based adhesive is a general-purpose choice on a porous primed wall, while hanging a heavy commercial covering over an existing vinyl wall calls for a vinyl-over-vinyl adhesive made for nonporous surfaces. Pattern layout affects the estimate as much as the installation. A large drop match means alternate strips are offset vertically to align the pattern, which raises waste substantially and must be carried in the material takeoff. Booking, the practice of folding a pasted strip paste-to-paste and letting it stand, allows the covering to relax and expand before it is hung so that it does not continue moving on the wall. A commercial specification calling for butt seams requires that adjacent strips meet edge to edge with no overlap and no gap. On the clear-finish side, an interior-rated polyurethane is the practical choice for an interior oak handrail in constant hand contact. Raw pine stains blotchy because its density varies, and a wood conditioner applied before the stain evens the absorption. Waterborne stain on maple raises the grain as the water swells the wood fibers, so the surface is de-nibbed lightly between coats. Light sanding between coats of a clear finish serves two purposes: it removes dust nibs and gives the next coat a mechanical key.
Solvents, Flash Point, and California VOC Rules
Match the solvent to the binder. Mineral spirits or paint thinner is the correct cleanup solvent for oil-based alkyd products; denatured alcohol is the solvent for shellac. Thinning is permitted only in the small, manufacturer-recommended amount and only for a stated purpose such as lowering viscosity so a spray gun atomizes properly. A safety data sheet lists each solvent's flash point, and a flash point well below room temperature tells you the vapors can ignite at ordinary jobsite temperatures. California regulates volatile organic compounds in architectural coatings differently from most of the country, and the structure of that regulation is tested. The California Air Resources Board publishes a Suggested Control Measure for architectural coatings, which is a model rule, but development, adoption, and enforcement of the actual limits are primarily the responsibility of the local air districts. So when a coating meets the statewide suggested control measure but not the rule of the air district where the job is, the local district rule governs, because the stricter limit applies. VOC content is expressed in grams per liter, calculated as grams of VOC per liter of coating excluding water and excluding exempt compounds; acetone, for example, is treated as an exempt compound rather than a counted VOC. Two consequences follow for the contractor. Field thinning a compliant coating with solvent to improve flow on a hot day can push the applied coating above its VOC limit, which is a compliance risk carried by the applicator. And the industrial maintenance coating designation carries a higher VOC allowance but is restricted to qualifying industrial uses, so it is not a loophole for residential work; similarly, air district rules provide narrow exemptions for certain small containers and specialty categories. A client who wants the lowest possible odor for a nursery repaint needs the painter to verify that the tinted product and the primer are also low-odor and low-emission, not just the base paint on the shelf.
Last updated: September 2026