Paints, Coatings and Materials Knowledge
This domain tests the composition and selection of coatings: what a paint is made of, which product suits which substrate and exposure, and how thinners, coverage and storage work.
Composition
Every paint has four parts - pigment (colour and opacity), binder or vehicle (forms the film; alkyd, acrylic, epoxy), solvent or thinner (carries it; water or white spirit) and additives (driers, anti-skin, fungicide, thickener). Film quality comes from the binder, so two paints of equal price differ mainly in binder content.
Product families
- Distemper: cheap interior finish on plaster, chalky and not washable.
- Cement paint: exterior masonry, tolerant of damp, powdery finish.
- Acrylic emulsion: water-based interior and exterior walls; matt, satin, sheen.
- Enamel (alkyd): solvent-based gloss for timber and metal; hard, washable, yellows less than old formulations.
- Primers and sealers: substrate-specific - wood primer, zinc phosphate metal primer, alkali-resisting masonry primer.
- Two-pack epoxy/PU: mixed in the stated ratio, used within the pot life, tough floor and wet-area finish.
Thinners and coverage
Water for emulsion, white spirit or turpentine for alkyd enamel, proprietary thinner for nitrocellulose lacquer. Never interchange. Typical coverage is 8–12 m² per litre per coat; the manufacturer's datasheet is authoritative, and two-pack products state a pot life of a few hours.
Worked example
Exterior plaster, coastal Odisha, monsoon exposure. Reasoning: the wall is alkaline and rain-driven. Choose alkali-resisting primer plus two coats of exterior-grade acrylic emulsion. Distemper and interior emulsion are refused because they chalk and wash away.
Traps that cost marks
Thinning emulsion with turpentine; adding thinner to two-pack after pot life; using gloss enamel on damp masonry; ignoring the shade card.