CoatQuotaHow much paint a room takes, coat by coat.

Exterior & Siding

Coverage by siding type — texture changes the spread rate more than the brand does.

Exterior paint quantities are decided by texture, and the gap between surfaces is far wider than the gap between brands.

Smooth fiber cement takes about 350 ft² per gallon. Lap siding 275, because every board has an underside the roller has to reach. Grooved or shiplap 225. T1-11 plywood 200. Stucco 160. Bare brick 125, because the mortar joints drink more than the brick does.

The "400 square feet" on the tin is measured on smooth primed drywall. It is the best case and it is never the case outdoors.

Two weather limits matter more than the gallon count

Surface temperature must stay above about 10 °C for the whole cure, not just while you are painting. A warm afternoon followed by a cold night gives a film that never properly coalesces, and it comes off in sheets the following spring.

Dew point matters as much as rain. Early-morning painting on a clear autumn day fails constantly for exactly this reason — the siding is wet with dew you cannot see.

Wash first, and then wait

Paint over chalky or dirty siding fails at the interface however good the paint is. Pressure-washed wood needs two or three dry days; a moisture meter reading under 15% is the honest test, not "it looks dry".

Back-roll anything you spray

Spraying lays paint on the surface. Back-rolling works it into the grain and the grooves. On textured siding that is the difference between six years and twelve.

Primer is a separate coat where the surface is porous

Brick, stucco and T1-11 need it, and on masonry a dedicated primer also seals the alkalinity that otherwise burns through the topcoat as patchy discoloration months later. On sound painted siding, spot-prime repairs instead.

Exterior paint

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