· by Michael Blair, Nashville's Handyman Service
Press a screwdriver into the bottom corner of a window sill, the base of a door jamb or the lower end of a corner board on almost any Nashville house more than fifteen years old and there is a fair chance it sinks in. Exterior trim takes the rain, sits in our humidity, and on the south and west sides bakes and cracks so it takes on more rain. The damage is nearly always at the bottom and at the end grain, and the choice between a repair and a replacement depends on how far it has traveled.
Finding how much is soft
Rot spreads inside the wood before it shows on the paint, so the visible damage understates it. Probe with an awl or screwdriver along the whole piece, not just the obvious spot. Sound wood resists; rotted wood gives with little pressure. Mark where it stops. Look at the adjacent pieces too, since rot at the base of a window casing usually means the sill under it is worse, and rot at the bottom of a door jamb often continues into the sill plate and subfloor behind it.
Also check what is behind. Pull a piece of the soft trim back if you can; the sheathing behind rotted trim on a house without proper flashing is often soft as well, and that changes the job from trim work to opening the wall.
When a repair holds
If the rot is confined to a small area, an inch or two at a corner or an end, and the piece is otherwise sound, an epoxy repair lasts. The soft wood is dug out completely, the remaining wood is dried and saturated with a liquid epoxy consolidant, and a two-part epoxy filler is shaped to the profile, sanded and painted. Done properly it is more durable than the wood around it. Done with a hardware-store wood filler, it pops out in a year.
A sill that is soft along its whole front edge, a jamb that is gone for the bottom foot, or a corner board rotted a third of the way up is not a filler job. The filler would be doing the work of the wood, and it will fail at the boundary.
- Small, contained soft spot on a sound piece: epoxy consolidant and filler
- Rot along an edge or up a length: cut out and replace the section or the piece
- Rot into the sheathing or framing: open the wall and fix the leak
- Any repair: prime every cut end before it goes back
Replacing the piece
A window sill can be cut out and a new one let in under the casing; a jamb leg can be cut above the rot and a new section scarfed on; a corner board is replaced whole. The replacement should be a material that will not do the same thing: a cellular PVC trim board, a composite, or at minimum a rot-resistant wood primed on all six sides including the cuts. Bare pine, which is what most builder trim was, is how the house got here.
Before the new piece goes on, the reason the old one rotted gets fixed. That is usually flashing: a missing drip cap over the window, no sill pan, house wrap lapped the wrong way, or a horizontal joint that catches water. New trim over the same missing flashing rots at the same rate.
Why it rotted, and keeping it from coming back
Water gets into trim at unsealed end grain, at joints where two pieces meet, at the gap where caulk has pulled away from siding, and from below where the trim touches a deck, a step or the ground. Middle Tennessee gives it the humidity to stay wet and the heat to grow the fungus that does the damage. The south and west faces suffer most because the sun cracks the paint that was keeping the water out.
Once repaired, keep every joint caulked with a quality exterior sealant, keep paint on the wood and especially on the bottom edges, keep trim off the ground and off the deck surface, and walk the house with a screwdriver every spring. A soft spot found at a quarter inch is a morning’s work. The same spot found two years later is a window.