Paints, Primers & Coatings: Choosing the Right Product

Welcome

Hello, and welcome. This is Super Structures General Contractors — a national general contractor headquartered in Powhatan, Virginia — here to help you and your clients build something that lasts. We're glad you're with us, and we look forward to connecting with you.

Alright, Paints, Primers & Coatings: Choosing the Right Product. Don't let the plain title fool you. Cut through everything, and it's this: Every coating is a chemistry chosen for a job — the data sheet tells you where it works, how thick to go, and how far it spreads, and the product that's right for one surface fails on another. Get comfortable here and you'll stop guessing at the paint counter.

A can of paint has four ingredients: pigment (color and hiding), binder (the resin that forms the film), solvent or carrier (water or petroleum solvent that evaporates), and additives. The binder sets the chemistry and most of the behavior.

The main families

• Latex / acrylic — water-based, the workhorse of architectural painting. 100 percent acrylic binders give the best exterior durability and adhesion; vinyl-acrylic blends cost less and suit interior walls. Fast drying, low odor, flexible, breathable, and resistant to alkali and UV.
• Alkyd (oil-based) — hard, smooth, high-leveling films on trim, doors, and metal; slower drying, yellows over time, higher VOC, and vulnerable to alkali. Waterborne alkyds now give the hard alkyd finish with water cleanup and have replaced most solvent alkyds on trim.
• Epoxy — two-component (resin and hardener) coatings with outstanding adhesion, hardness, and chemical resistance; the primer and intermediate coat of most industrial systems and the standard for floors. Chalks in sunlight, so it's topcoated outdoors.
• Polyurethane / urethane — two-component topcoats that hold gloss and color in UV; the finish coat over epoxy on bridges, tanks, and exposed steel.
• Elastomeric — thick, stretchy acrylic coatings for stucco and masonry that bridge hairline cracks and shed water, applied at several times the thickness of ordinary paint.
• Primers — chosen for the substrate: drywall primer-sealer (PVA), stain-blocking primers (shellac, alkyd, or acrylic), bonding primers for glossy surfaces, rust-inhibitive and zinc-rich primers for steel, and block filler for CMU.
• Specialty — direct-to-metal (DTM) acrylics, dryfall for exposed ceilings, intumescent coatings for fire-rated steel, anti-graffiti, antimicrobial, and floor coatings.

Sheen

Sheen is how much light the dried film reflects: flat/matte, eggshell, satin, semi-gloss, and gloss. Higher sheen is harder and more washable but shows every flaw; lower sheen hides defects and touches up more easily. Ceilings are usually flat; walls eggshell or satin; trim, doors, kitchens, and baths semi-gloss. MPI gloss levels run G1 (flat) through G7 (high gloss), and specifications often call out sheen by MPI gloss level rather than a brand's name.

VOC rules

Volatile organic compounds are the solvents that evaporate as paint dries; they contribute to ozone and affect indoor air. The EPA sets national limits for architectural coatings under 40 CFR Part 59, and several regions are stricter — California's air districts (including SCAQMD Rule 1113) and the Ozone Transport Commission states in the Northeast. Green building programs set their own limits. VOC content is on the data sheet, and the spec usually says which limits apply.

Thickness and spread rate

Coatings are specified by film thickness in mils (thousandths of an inch). The data sheet gives a wet film thickness (WFT) to apply and the dry film thickness (DFT) it leaves once the solvent is gone; the ratio is the product's volume solids. A painter checks WFT with a notched gauge during application; on steel, DFT is measured with a magnetic gauge under SSPC-PA 2. The spread rate (square feet per gallon at the recommended thickness) sets how much material the job needs — and a crew that spreads a gallon farther than the data sheet allows has applied a thinner film than the warranty requires.

The data sheet

Every product has a product data sheet (PDS) and a safety data sheet (SDS). The PDS lists recommended substrates, surface preparation, compatible primers, thinning, application methods and spray tip sizes, WFT/DFT, spread rate, dry and recoat times at a stated temperature and humidity, application temperature limits, VOC content, and the pot life of two-component products. The SDS covers hazards and protective equipment. Both belong on the job.

Going Deeper (Intermediate)

Hiding depends on pigment quality, mostly titanium dioxide, and on film thickness; a cheap paint stretched thin takes three coats to do what a quality paint does in two. Deep colors carry less titanium dioxide and may need a tinted primer to hide in two coats. The painter should box (intermix) all cans of a color before use so slight batch differences don't show as a line on the wall.

Temperature and humidity change everything: most latex paints need the surface and air above about 50°F (some newer formulations go lower) and won't coalesce into a sound film if it's colder or if dew settles on them overnight. Two-component products have a pot life after mixing and a recoat window; miss the window and the next coat won't bond without sanding.

Advanced / Pro-Level

Pros specify and buy systems, not cans: for exposed structural steel, for example, a blast to SP 10, an organic zinc-rich primer, an epoxy intermediate, and an aliphatic polyurethane topcoat, each at a specified DFT, all from one manufacturer so the warranty covers the whole stack. They calculate material from theoretical coverage — 1,604 square feet per gallon at one mil for a 100-percent-solids product, scaled by volume solids and target DFT — then add a realistic loss factor for spraying, roughness, and waste. They read the MPI Approved Products List when a spec cites MPI numbers, because that list, not the brand name, decides what's compliant.

They also understand substitution: an "or equal" product has to match the specified product's binder type, solids, DFT, and performance, and the architect has to approve it in writing before it goes on the wall.

Practice Challenge

A spec calls for an acrylic eggshell at 4 mils WFT with a spread rate of 400 square feet per gallon. The crew reports they're getting 600 square feet per gallon. What's wrong? (Answer: spreading the paint 50 percent farther than the data sheet allows means the film is far thinner than specified — roughly 2.7 mils wet instead of 4 — so hiding, washability, and the warranty are compromised; the crew needs to check WFT with a gauge and apply the material at the specified rate.)

In Practice

A painter who reads the data sheet and applies the specified film passes a DFT check and never hears about the job again. A painter who stretches a gallon to save material repaints when the walls flash and the color reads thin under the lights.

Common Mistakes to Avoid

• Using an alkyd on fresh masonry or concrete
• Choosing a product by price without checking the substrate and exposure on the data sheet
• Spreading paint beyond the data sheet's spread rate, leaving the film too thin
• Ignoring temperature, humidity, pot life, and recoat windows

Takeaway: Every coating is a chemistry chosen for a job — the data sheet tells you where it works, how thick to go, and how far it spreads, and the product that's right for one surface fails on another.

Educational overview only — not hands-on painting or coatings instruction, a safety program, or a substitute for training under an experienced painter or coatings applicator. Follow OSHA, the EPA RRP rule, your state's contractor licensing requirements, the project specifications, and the coating manufacturer's data sheets for your work.