How To Repair An Exterior Rotted Window Sill

Q: 1 of our windowsills appears to exist rotting. Tin it be replaced without buying a new window?

—Bill Bailey, Baldwin, Mo.

David Raymond, Raymond Blueprint Builders, replies: Sticking out into the weather year later twelvemonth, woods windowsills accept quite a beating. They can last for decades if you but keep them clean and protect them with a coat of paint. Merely when h2o gets trapped in or against them, as happens with improperly flashed windows, rot can take agree.

A simple epoxy repair will do the flim-flam if the rot is confined to a small area, but if more than x percent of the sill is rotten, the one-time sill should exist cut off and replaced. For this project, I used a solid piece of Kleer cellular PVC sill that matches the profile and thickness of the other sills on the firm. Information technology costs less than a piece of articulate, milled cherry-red cedar and is paintable, just no matter how many times it gets moisture, information technology can't rot.

Step-by-step tutorial renders beneath OTHER VIDEOS thespian. Keep scrolling!

Footstep 1

Remove the Side Casings

The casing comes off to clear the style for removing the sometime sill. If the casings are rotting, equally here, replace them, too. Slice through the caulk bead between the siding and the casing, and then carefully pry off each piece. Save the trim to use as templates for the new ones. Make sure the flashing behind the casing is intact and properly installed behind the siding.

Step 2

Saw Off the One-time Sill

Make a plumb cut affluent with the sheathing along the length of the rotten sill. A circular saw with a askew blade can handle most of the cutting, only for the sill ends where a circ saw can't reach, switch to a multitool, like this Fein Multimaster equipped with an oscillating saw blade. Smooth the cut with a few strokes of a manus plane.

Footstep 3

Utilize the Adhesive

Repair any rotten spots on the old sill with epoxy. Trim the dorsum edge of the new sill as needed so that its lower border fits tightly against the siding and its dorsum border fits against the old wood. Drill pilot holes every 16 inches or so through the new sill's front and back edges. Run a bead of waterproof, marine-grade adhesive forth the quondam sill.

Footstep 4

Adhere the New Sill

Press the new sill into the adhesive, and immediately clamp information technology in place by driving 3½-inch deck screws through the plastic and into the woods. Stop when the heads are virtually ¼ inch below the sill surface. Immediately wipe upwardly any agglutinative that squeezes out. Make full whatsoever gaps betwixt the old and new sill with adhesive.

Step 5

Hibernate the Screwheads

Cover each screwhead with a dollop of a white, 2-part acrylic adhesive, such as Bond&Fill FastCure. (This as well works as an adhesive in Step iii.) Overfill the recess slightly. When the adhesive hardens completely, in about 30 minutes, sand it affluent.

Footstep vi

Install the Side Casing

Squeeze a bead of caulk abreast the ends of the siding, and smash the new casing in place. Here, I used cellular PVC trim boards and 8d stainless-steel band-shank nails. Set the nailheads slightly below the surface, and comprehend each one with a dab of the two-part adhesive. Subsequently the dabs harden, sand them flush.