How to Repair a Box Sash Window

Repairingany window canbe difficult, but the box sash, being such an old style, means that some properties have been left without maintenance for long periods of time to try to preserve their sashes’ authenticity. Older varieties, as such, can become liable to damage, and notoriously draughty. Many companies can upgrade your sash windows by implementing modern double-glazing for added security and draught exclusion, among other things. But this tends to be expensive, and not everyone may be prepared to spend. However, it is also possible to repair damaged box sash windows yourself. But we only recommend it, if you have the proper knowhow first.

Before doing anything, you need to determine the problem. Some problems can’t be fixed so easily and may require specialist attention, for warped wood example. But, for something like improving draught-reduction, our guide is just what you need.

Firstly, it is necessary to remove the sash, to get a better look at how it can be fixed. If the wood is warped or damaged, you may want to consider commissioning a replacement sash, if you’re not in the market to have them all upgraded. Then, unscrew the moldings on the lower sash and remove it, tying the cords into knots to stop them being pulled back into the weight pockets. You can then pullout the upper sash, separating it from its cords or chains, storing all extraneous pieces safely for later.


Use a heat gun to soften the old or hardened putty, scraping it away with a putty knife, prying the glazier’s points out once exposed, to free the glass. Then, using a rotary tool, grind away any softened or rotted wood at the joints. Afterwards, apply an epoxy primer, leaving it to set for no more than 20 minutes. Then feed more of the epoxy mixture into the joint, spreading it over the sides to restore its shape.Once set, usually overnight, you’ll need to use sandpaper to sand down the sash, sealing the wood with an oil-based primer. Exterior side facing up, you can thenroll your glazing compound (in place of the original putty) into a long vine shape, to be pressed into the grooves around the pane openings. Press the pane gently into the glazing compound until properly bedded.

Once done, slide each new glazier’s point on the glass and push it into the sash. Then, pressing another piece of the glazing compound around the edge of the pane, you need to make a smooth bevel between the sash and the glass, using a knife for each pane. After about a week, coat the putty using acrylic latex and apply paint.

Finally, clean and reattach the hardware and weather-stripping if nothingneeds replacing.Hook the cords onto the lower sash and replace both stops to hold it in place. There you have it. You’ve restored and repaired your original sash windows.

For all your sash window queries and needs, you should talk to The Original Box Sash Windows Company or visit their website at Guaranteed, they can offer you something to suit your needs.