Wood Window Restoration & Repair

Wood window restoration and repair is something that needs to be done about every 50 years. If you wait until your windows are in an emergency state of repair, you’re taking a risk and the task of wood window restoration will that much more involved.

Replacement window companies will often compare their product to a neglected historic wood window that has NOT been restored or maintained – an old wood window that would undoubtedly be drafty and inefficient.

Window companies will boast that their windows are Maintenance Free. That is true because Maintenance Free means Cannot be Maintained. Their replacement windows will be in the landfill in 20 years.

Wood window restoration and repair is easier than you think. Old wood windows were made to be repaired. They can easily be taken apart to insert new rails or muntins (cross pieces separating the panes). Broken parts can be remade or whole sashes can be duplicated. They can last 200+ years.

Rotted wood can be repaired to look like new with easy-to-use epoxy fillers designed for wood window restoration (see Abatron ad below). In many cases, these windows have been in service for over a hundred years with much of their deterioration resulting directly from a lack of maintenance.

Your windows are made from old wood which does not compare to the wood of today .

With repairs and regular maintenance, the life of these old wood windows can be extended for an additional 200 years.

You are a steward to and old building with old windows. Please be responsible and Do NOT neglect your old windows.

How to Repair Sash Windows

How to preserve old windows with putty, epoxy, and patience

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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

Photo by David Carmack

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

Photo by David Carmack

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

Photo by David Carmack

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

Photo by David Carmack

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

Photo by David Carmack

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

Photo by David Carmack

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

Photo by David Carmack

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

Photo by David Carmack

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

Photo by David Carmack

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.

Repair a Wood Window in 12 Steps

Pro tips for glazing and painting wood sash like an expert.

Reglazing windows is often the first step to improving their efficiency. (Photo: LordBPhotos/Fotolia.com)

Window designs have evolved over centuries to enhance the beauty of a building, keep out the storms, let in the breeze, and give you a view of the trees, the moon, and the universe beyond. Not to mention, they’ve held up to decades of use and abuse. But with a round of maintenance and a few repairs, old wood sash windows will easily last another century.

Window glazing is a combination of science and art that can only be developed with experience. As a beginner, start with sash from the barn or back room, where your early results will be good enough as you improve your technique. Once you have done 10 sashes, trying to do better each time, you’ll be more proficient. By the time you get around to the front windows, your glazing will look just fine.

Step 1: Pre-treat, if needed

This step may not be needed if all wood surfaces are perfectly sound. If the bottom edge of the lower sash’s bottom rail is in good condition, it doesn’t need treatment since it has done well bare for so many years. However, if it shows signs of water deterioration, give it a coat of pre-treatment.

When you apply a pre-treatment to the bare wood [A], put it on the sash (both faces), muntin bars, and muntins. If you are using consolidating oil, put it in the glazing rabbets, too, and also add extra at each joint so it soaks in and treats the end-grain within. (Be careful not to apply pre-treatment to the side edges of the sashes and top edge of the upper sash.) Let the treatment dry before proceeding.

If you’re not going to pre-treat the entire sash, apply a consolidating oil or linseed oil mixture to the glazing rabbet. This prevents the wood from absorbing too much oil from the putty, which can lead to putty adhesion problems.

Safety Tip: Old windows usually contain lead paint—always follow lead-safe work practices. For more information, visit epa.gov/lead.

Step 2: Sand wood surfaces, if needed

All surfaces and arrises should feel smooth. Sand off nibs and whiskers, then dust with a HEPA vacuum and tack cloth.

Step 3: Prime the sash

Prime all the surfaces of the sash except the side edges (that run in the tracks) and the face margins. Do not prime the glazing rabbets if they were pre-treated with an oil-resin. Allow to dry thoroughly.

If you are priming the glazing rabbets, start by brushing a little puddle of primer on at each joint [B]; it will soak into the joint and help seal the end-grain. Leaving some primer puddled on the surface at the joints also makes it easier and quicker to get primer into the corners when you come back to brush the primer out across the surface.

Step 4: Sand primed surfaces, if needed

As above, sand off any nibs and whiskers until all surfaces feel smooth. Dust with a HEPA vacuum or brush and tack cloth. Re-prime any spots or areas of bare wood where sanding removed the primer.

Step 5: Bed the pane

Start by making sure all the panes fit by laying them in place in the sash. When you take them out, keep them in an order you can remember so they go back where they belong. (I lay the panes out on the bench in the same arrangement; some stick on blue painter’s tape and number it.) Warm up the putty by kneading it in your hand, then press the putty into the glazing rabbet with your fingers, thumb, or the heel of your hand [C].

Next, lay a “bed” of putty in all the glazing rabbets of the sash. Place each pane of glass on the bedding putty, making sure the bottom edge of glass rests on the neck of the lower glazing rabbet.

Jiggle the pane slightly with your fingers along the edges so it beds down into the putty. Leave at least 1⁄16″ of back putty between the glass and the shoulder of the glazing rabbet. You should have some putty squeezing out along all the edges of the glass.

Panes wider than 24″ may require spacer blocks between the edges of the glass and the neck of the glazing rabbet—little pieces of wood or plastic that help secure heavier panes until the putty firms up.

Pro Tip: You can quickly “bed” the pane down into the putty using an electric palm sander with a rubber pad (no sandpaper). Only use a new (low-cost) palm sander to avoid scratching the glass with any residual grit. Turn the sander on, and touch the rubber pad on the glass for a quick second or two. Be careful; it’s easy to squeeze too much putty out of the bed—leave at least 1/16” of putty between the pane and the shoulder of the glazing rabbet.

Step 6: Set glazing points

Set at least one point per edge on panes smaller than 6″ or 8″. On larger panes, set points away from the corners of the glass at least one-fourth the length of the edge, and then every 8″ to 10″ in between.

Lay the point flat on the glass with the sharp end leading into the neck of the glazing rabbet [D]. Set the edge of the putty knife across the tabs and wiggle it side-to-side, pushing the point into the wood until the tabs are flush with the neck of the glazing rabbet [E]. (The wiggle helps ease the point into the wood with less stress on the glass.) You may have to hold thin muntins from behind to keep from breaking the rib or muntin.

Pro Tip: You can set points much faster with a point driver. Load the magazine with diamond or triangle points, set it gently onto the pane, and squeeze the trigger—the spring-loaded mechanism shoots a point into the neck of the glazing rabbet. Be careful to squeeze the trigger up, and don’t push down on the handle (as you would with a staple gun), which can break the glass.

Step 7: Tool the face putty

Go around the entire sash, placing and packing lines of putty; it doesn’t have to look good at first. Some people roll the putty into little snakes—you can do this, but it takes extra time. I like to quickly distribute the putty using the palm of my hand or a putty knife.

Next, pack the face putty into place—put the end of the putty knife on the pane and wiggle the knife slightly to force the putty into place [F]. It still doesn’t have to look good.

Finally, tool the surface of the face putty using the “end edge” or “in line” technique (see below) to form an even bevel that looks good and packs putty firmly into the glazing rabbet, forming a good seal all along the glass and wood. You should be able to look through the pane and see that the edge of your putty is directly across from the arris on the other side of the glass. Form neat miters at the corners, where the bevels meet.

Tooling Technique: End Edge
Keep the edge of the putty knife on the glass through most of the stroke. This technique leaves no putty on the glass, which saves time. Hold the knife at a slight angle to compress the putty into the glazing rabbet during the stroke, leaving a smooth, flat bevel of putty. Stroke slowly to allow the putty to “flow” onto the underneath side of the knife.

Tooling Technique: In Line
Hold the knife at a slight angle so the putty compresses into the glazing rabbet and leaves a smooth, flat bevel of putty. This technique leaves a little putty on the glass that you will have to go back and remove. I like to do so by taking my warm wad of putty, forming it into a ridge, and wiping it along the edge of the pane, which picks up the waste putty.

Step 8: Polish and clean the pane

Immediately after tooling, you’ll need to polish the outside of the pane with whiting to clean oil from the putty off the glass and “dust up” the putty’s surface to promote drying.

Tamp a dry, soft-bristled 3″ or 4″ paintbrush into the dry powdered whiting and work a small amount into the bristles. Starting at the top of the panes, gently dust the surface of the glass with the brush [G]. Work down the panes to remove all the whiting and oil from the glass surface. It’s OK to brush the surface of the putty, but be careful to not jam the ends of the bristles directly into it.

Sweep any remaining buildup of whiting out of the lower corners, and finish with wide, sweeping diagonal strokes, which leaves the pane clean, clear, and free of oily fingerprints and whiting.

Safety Tip: When polishing with whiting, wear goggles and a respirator to keep it out of your eyes, nose, mouth, and lungs.

Step 9: Tool the back putty

Flip the sash over, and use a putty knife to trim off the excess putty that squeezed out from the bedding [H].

Step 10: Polish and clean the panes

“Polish” the inside of panes with whiting, as in Step 8. Then set the sash aside to let the putty cure. (Cure times will vary depending upon the putty used and the environmental conditions.) Place the sash in correct vertical position, exterior side out, and lean it slightly back to avoid distorting the putty bevel.

Step 11: Prime the putty, if needed

Some putty and paint combinations need to be primed; others don’t—check the manufacturer’s recommendations. Apply primer to face putty bevels and interior seals, lapping it 1⁄16″ onto the glass. Let dry.

Step 12: Paint the sash and putty

Brush two topcoats of paint onto the entire sash (except the side, top, and bottom edges if they’re not being painted), lapping paint 1⁄16″ onto the glass, which seals out rainwater and extends the putty’s service life. Use high-quality enamel or exterior house paint. Waterborne 100-percent acrylic paint is good, as are oil-based alkyd resin or linseed oil paints.

If you use acrylic house paint, be sure to take a rag and wipe off the side margins of the sash [I] and the meeting surfaces of the meeting rails. This will help prevent the sash from sticking to the sash track and stops.

Online Bonus: Window Repair Video

See Part 2 and more videos at Historic HomeWorks.