Sooner or later, somebody drills a hole through a sash window that shouldn't be there. Usually it's for a cable. An old alarm sensor, a phone line that got moved, an aerial lead run through the frame instead of around it. Whoever did it needed the cable through the window at the time, and once the job that needed it was gone, the hole stayed.
We came across exactly this on a recent job: a neat round hole punched straight through the bottom rail of a bedroom sash, left over from a cable that had long since been removed. The rest of the window was sound. It just had a hole in it that let draught and moisture straight into the timber.
The hole left behind once the cable it was drilled for was gone.
Why you don't just leave it
A hole through a sash rail isn't only a draught problem, though it is that. Bare end grain and exposed timber inside the hole soak up moisture every time it rains sideways or condensation sits on the glass overnight. Left alone, a clean drilled hole slowly turns into a soft, rotten one, and a job that would have taken an hour turns into a rail replacement.
It also isn't worth papering over with a bit of filler from the hardware aisle. Standard interior filler shrinks, it doesn't bond well to old painted timber, and it has no gap filling strength, so it drops out the first time the window is slammed shut. This is exactly the kind of small structural repair a two part wood epoxy is built for.
How we patched it
The method is the same one we use across most of our timber repairs, whether it's a cable hole, a screw hole from an old lock, or a small patch of surface rot. We keep it to four steps on site.
1. Clean out the hole
Any loose or splintered timber gets cleaned back to solid wood first. A patch only holds as well as what it's bonded to, so soft or crumbling material has to go before anything gets mixed.
2. Mix the epoxy
We use a two part DT wood repair epoxy with a one hour cure, which is the standard repair product across our jobs. It's mixed in small batches on a scrap of cardboard, just enough for the patch at hand, since it starts curing the moment the two parts meet.
3. Fill and press
The epoxy gets pressed firmly into the hole with a putty knife, slightly proud of the surrounding timber so there's material to sand back once it's cured. Because it's a genuine gap filling epoxy rather than a shrinking filler, it doesn't need to be built up in thin layers the way some products do.
4. Sand flush and paint
Once cured (around an hour later, hence the name), the patch is sanded back flush with the surrounding rail. At this stage it still shows as a slightly different colour patch, which is completely normal and disappears once it's primed and painted over.
Filled and ready to sand back flush before painting.
An hour after mixing, that hole was gone. No rail replacement, no waiting days for a slow cure, no visible repair once it was painted.
Doing this one yourself
This is a genuinely easy weekend repair if you're comfortable with basic tools. A drilled cable hole, an old lock mortise nobody wants anymore, a small patch of surface rot on a sill, they all get treated the same way.
- Clean the hole or damaged area back to solid, sound timber
- Mix a small batch of two part wood epoxy, only as much as you'll use in the cure window
- Press it in firmly with a putty knife, slightly proud of the surface
- Let it cure fully before sanding flush
- Prime and paint to match
We stock the same DT wood repair epoxy with a one hour cure our crews use on site, along with an epoxy gun for larger jobs and an epoxy wood stabiliser for timber that's gone soft rather than just holed. If you're setting up to do a few repairs around the house, the DT epoxy starter pack has everything in one box.
If the hole in your window is bigger than a cable run, or the timber around it has gone soft, have a look at our guide on filler versus epoxy for timber repairs to work out which approach suits the damage. We used the same epoxy for a bigger job on raising a dog door by 110mm, if you want to see it handle a larger fill.
The same window, back in one piece.