How Hot Weather Affects Exterior House Painting
A sunlit elevation is far hotter than the forecast suggests. Here's how surface temperature changes exterior painting, and how to plan the day around it.
The Wall Is Far Hotter Than the Forecast
On a 28°C day, a south-facing brick or render elevation in direct sun can reach well over 40°C. Most exterior paints state a maximum surface temperature, and it is easily exceeded.
Paint applied to a surface that hot flashes off instantly, leaving poor adhesion, visible laps and a finish that fails early.
The practical test is simple: if you can't comfortably hold your palm flat on the wall, it is too hot to paint.
Work Around the Building, Not Against the Sun
Plan the day by elevation. Take the east side in the afternoon once the sun has moved off it, and the west side in the morning.
Never paint the face the sun is on, however convenient the scaffold position makes it.
Avoid finishing an elevation late in the evening in summer too — dew forming on paint that hasn't cured causes bloom and patchy sheen.
Flexible Coatings and Honest Recoat Intervals
Use flexible masonry paint that can move with the daily expansion and contraction of a hot elevation, and UV-stable trim paint on joinery.
Fast surface drying is misleading — the coating may be touch dry in under an hour but nowhere near cured. Respect the stated recoat interval rather than the way it feels.
Dry masonry is very absorbent after a long hot spell. A stabilising primer stops the topcoat being drawn in and drying chalky.
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