How to Repair Sash Windows

Single-pane double-hung windows from the 19th ­century don’t have the best of reputations. They can be notoriously drafty, full of rattles, loose in the joints, or can simply refuse to budge. But as a number of studies have shown, when these windows are properly weatherstripped and paired with good storm windows, they can match the performance of new double-pane units for much less than the new ones cost.

Painting contractor John Dee, whose refinishing skills are regularly seen in the pages of This Old House, recently turned the windows in an 1882 house back into smooth operators—and increased their energy efficiency, to boot. As he shows on the ­following pages, it was simply a matter of methodically removing each sash from its opening, stripping off the old paint and putty, and regluing the joints with epoxy. With new putty, ­paint, and weatherstripping, the sash are ready to face the cold and last through the 21st century as good as new.

Painting contractor John Dee reattaches the stops, the last step in his window restoration. “Before this, opening a window was a wrestling match,” he says. “Now, they just glide up and down.”

Step 1

Get the Sash Out

Pry off or unscrew the stops (the moldings in front of the lower sash).

Pull out the lower sash, and take off the cords or chains on both sides.

Knot the cords to keep them from being pulled into the weight pockets.

Remove the parting beads (the vertical strips holding the upper sash).

Pull out the upper sash, and take off its cords or chains.

Remove the sash hardware and store in a labeled bag.

Step 2

Free the Glass

Soften old, hardened putty (glazing compound) with a heat gun set to medium and fitted with a nozzle shield. Scrape the putty away with a putty knife. This exposes the metal glazier’s points; pry them out of the wood. Remove the glass, and label it so you know which opening to put it back into.

Step 3

Clean Out the Joints

Using a rotary tool such as a Dremel, grind away any soft or rotten wood wherever sash joints are loose or open.

Step 4

Apply the Epoxy

To rebuild the cleaned-out joints, first brush on the epoxy primer and let it set for about 20 minutes. Then, using a plastic scraper, mix the two parts of the epoxy filler into a goop the consistency of Vaseline. Force it into the joint, and spread the mix over the sides to restore the joint’s original shape. Wait overnight, then trim the excess with a utility knife.

Tip: Clamp pieces of Plexiglas over the wet epoxy. When it hardens, take the plastic off. You’ll have a smooth surface that doesn’t need much sanding.

Step 5

Prime the Sash

Wait another day, until the epoxy is fully cured, then hand-sand the sash with 100-grit paper, and wipe up all the dust with a tack cloth. Seal the wood with a coat of oil-based primer.

Tip: “Without a coat of primer, the wood will suck the oils out of the putty and turn it brittle prematurely.” —John Dee, painting contractor

Step 6

Bed the Glass

Lay the sash exterior side up. Roll glazing compound into a long rope, between your hands and press it into the groove, or rabbet, around the pane opening. Gently press the pane evenly into the compound until it’s bedded about 1/16 inch from the bottom of the rabbet.

Step 7

Insert the Points

Using a putty knife, slide each new glazier’s point on the glass and push it point first into the wood sash. Plant at least two points, evenly spaced, on each side of the pane. For large panes, the spacing between the points should not exceed 12 inches.

Tip: “On warm days, lubricate the tip of the putty knife with linseed oil so that it doesn’t pull out the glazing compound.” —John Dee

Step 8

Tool the Putty

Press another rope of compound around the edge of the pane. Make a smooth bevel between the glass and sash by pulling a putty knife over the compound. Repeat on the other panes. Wait at least a week, then coat the putty with oil-based primer. Apply a top coat of acrylic latex paint to the putty and sash.

Step 9

Rehang the Sash

If the windows have old weatherstripping, replace it; if there isn’t any, add it. (See instructions for weatherstripping a window.) Clean and reattach the hardware; lubricate the pulley axles with a silicone or Teflon spray. Reattach the cords or chains to the upper sash, and reinstall the parting beads or replace them with new ones. Hook the cords or chains to the lower sash, then put both stops back on the jamb to hold the restored sash in place.

Tip: Strip paint-encrusted hardware by giving it an overnight dip in a warm Crock-Pot filled with sudsy water.