Signs of Wood Rot on Exterior Trim: Where to Probe and What Soft Wood Means for a Paint Job
Wood rot is fungal decay in wood that stays wet, and on most houses it starts in the same handful of places. Paint failure is often the first sign: paint that peels in the same spot every year usually has water, and often rot, underneath.
Where to Probe
Use a screwdriver or an awl. Sound wood resists; rotted wood is soft, spongy or crumbles.
- Window sills and the bottom of window casings
- Bottoms of door frames and brick molding, where water pools on steps and concrete
- Garage door trim at the bottom
- Fascia boards behind gutters that overflow
- Corner boards and siding bottoms near the ground, decks or roof lines
- Porch columns and rails, especially at the base
Other Signs
- Dark staining or black lines along a board's edge
- Paint blistering or bubbling on trim
- Gaps where caulk has pulled away
- Swollen or cupped boards
- Mushroom-like growth in severe cases
Rot or Termites?
Rot and termites both like damp wood. Mud tubes on the foundation, hollow-sounding wood, tunnels in the wood or winged insects point to termites. If you find signs of insects, call a pest professional before repairs.
Why It Matters for Paint
Paint cannot hold soft wood together. Painting over rot seals the surface for a season while the decay keeps spreading underneath, and the paint fails again. Rotted wood has to be cut out and replaced (or, for small areas, stabilized with epoxy), primed, caulked and then painted.
Frequently Asked Questions
Can wood filler fix rotted trim?
Only very small, shallow spots. Larger areas need the rotted wood removed and replaced.
Should I use PVC trim for replacements?
For spots that stay wet, like door frame bottoms, PVC is a good choice because it does not rot.
How fast does wood rot spread?
It depends on how wet the wood stays. In a wet spot it can spread through a board within a few seasons.
What causes rot on new houses?
Missing flashing, unprimed cut ends, sprinklers and splash-back can rot trim on houses only a few years old.
Found a Soft Spot?
We probe the whole house and list every repair before an exterior repaint. See wood rot repair or contact us.