Paints and Building Coatings

Building paints fall into three practical groups. Water-based products such as emulsion and acrylic serve interiors, with low odour, low volatile content and quick drying. Acrylic and silicone facade paints must resist ultraviolet exposure while still allowing vapour to escape the wall; a facade coating that seals the surface completely traps moisture and blisters off. The third group is protective coatings for steel: anti-corrosive primers, epoxies and intumescent fire-protective paint for structural frames.

Paint is always a multi-layer system, and dropping any layer shortens the life of the whole. A typical interior sequence is filling and sanding, primer, then at least two finish coats. Primer is not simply an extra coat; it evens out substrate absorption and creates adhesion, and paint applied to fresh plaster without primer dries patchy and uneven. Emulsion covers roughly 8 to 12 square metres per litre per coat, with a dry film thickness of about 25 to 40 microns per coat.

The single biggest error is painting over a damp substrate. Plastered surfaces must dry fully, with moisture content below roughly 5 per cent before painting; otherwise the film blisters and peels within months. The second error is over-thinning paint to stretch coverage, which reduces film thickness and with it opacity and washability. The third, on facades, is painting a surface whose cracks have not yet been repaired and sealed.

When choosing colours, view samples on the actual wall in daylight rather than from a catalogue. Colour reads very differently under artificial light and at small scale, and the gap between the shade chosen and the shade delivered is the most common source of complaint at handover.