Diagnosing flaking paint on outside joinery

Reading where the flakes start

Flaking that begins at a sill, a horizontal ledge or a butt joint almost always means water ingress from that point, travelling under the film until it lifts. Flaking spread evenly across a whole face is more often a coating that was never suited to timber movement in the first place, particularly older alkyd systems gone brittle with age.

• Sills, horns and joints checked first with a moisture meter
• Flake edges examined for how many coats are lifting together
• Back of the window and reveal checked, not just the visible face

Why hard old paint fails on soft new movement

Timber swells and shrinks with the seasons. A rigid oil-based film applied decades ago has often lost the flexibility to follow that movement, so it cracks at the grain and then peels once water gets behind the crack. Recoating over it without removing the loose layers just gives the new paint the same weak base.

What proper preparation looks like here

Loose and flaking material comes off back to sound paint or bare timber, feathered so the edge does not telegraph through the new coat. Any decayed wood is cut out and repaired before priming, because painting over soft timber only delays the same failure.

• Loose paint removed mechanically, not just sanded flat over the top
• Bare timber spot-primed the same day it is exposed
• Repaired sections given an extra coat to match film build