How to Fix Wood Rot Before Painting (And Why It Matters)
What is wood rot and why can't you just paint over it?
Wood rot is timber that has been broken down by moisture and fungal decay. It's one of the most common problems we find on windows, doors and exterior woodwork across SW London's older housing stock. Painting directly over rotten timber doesn't fix anything. The paint film might look fine for a few months, but the wood underneath keeps breaking down. The new paint will crack, bubble and fail within a short space of time. The rotten section has to be removed and treated first.
How do you tell if a window or door has wood rot?
Common signs include a soft or spongy feel when you press the timber, paint that's flaking, blistering or peeling in one specific area rather than evenly across a surface, a dull or darkened patch of wood and small cracks running with the grain. Wood rot tends to show up first at joints, sills and anywhere water can sit or get trapped, such as the bottom of a window frame or the base of a door.
How we repair wood rot before painting
The process is the same whether it's a single window or a full exterior:
Remove and treat the affected timber. The rotten section is removed and the remaining wood treated before anything else happens.
Fill. We use Repair Care wood filler, a specialist wood repair system designed to bond properly with timber and resist further moisture damage, rather than a general-purpose filler that will fail in the same way the original problem did.
Sand smooth. The filled area is sanded back so it's flush with the surrounding wood.
Prime and undercoat. Bare, filled timber needs both a primer and an undercoat before any topcoat goes on.
Topcoat. We typically apply three coats of an exterior-grade paint such as Zinsser AllCoat Exterior or Dulux Weathershield, depending on the surface and finish required.
Real examples from recent jobs
On one window repair, the timber had rotted away enough that the affected section had to be removed entirely before the process above could start, with the masonry windowsill beneath it reshaped, filled, sanded back and repainted in Dulux Weathershield Smooth Masonry.
On a front door and gate with years of built-up paint, the issue wasn't rot alone but layers of old paint that needed stripping back to bare wood first, after which the same fill, sand, prime, undercoat and topcoat process was followed, finished in three coats of Dulux Weathershield.
On a larger exterior project, wood rot on a number of windows was treated and repaired with Repair Care filler. At the same time, the masonry was repaired and repainted; railings had their loose paint removed and repainted; and leadwork was stripped of loose paint and refinished with a specialist lead paint. Treating everything as one job, rather than patching the woodwork and ignoring the rest, gave a consistent, properly prepared finish across the whole exterior.
Why this matters
Skipping proper wood rot repair is the single biggest reason exterior paintwork fails early. A few extra days spent removing, treating and filling rotten timber properly is what makes the difference between a paint job that lasts a couple of seasons and one that lasts for years.
Spotted wood rot on your windows, doors or exterior woodwork? Get in touch for a free, no-obligation quote
