Restoring Window Sashes

Synopsis: A restoration carpenter argues that old windows are often worth saving, then provides detailed instructions for stripping, repairing, painting, and glazing the sashes. A sidebar offers tips for removing old sash.

Other than a lighted match, nothing will ruin the charm of an old house faster than ripping out the original double-hung windows. But if your windows are old enough to have sash cords, pulleys, and weights—and especially if they’ve fallen into disrepair—you might be tempted by those ads that promise huge energy savings and no maintenance if you replace the windows. What they won’t tell you is that energy-wise, you’d get a much better return on your investment simply by repairing existing windows and adding high-quality storm windows.

From my perspective, it makes no sense to remove window units that have survived for a century or more and to replace them with something that may not last a decade before the finger-jointed wood frame rots or the vinyl cladding deteriorates or the double glazed seals rupture. Why not spend a little time, and a lot less money, to help your existing windows last another century?

They Don’t Make Them Like They Used To

Materials vary by region, but most of the old windows that I see are crafted from first growth, vertical-grain pine. This remarkable stuff is dimensionally stable and highly rot resistant, far superior to anything available today. Old-growth pine is so durable and forgiving that even though they may look bad, most of the windows I’m asked to repair (or replace) generally require little more than minor touch-ups and a bit of reglazing.

If your house is 100 or more years old and if you’re lucky, you still might have the original hand blown glass. This important feature denotes early windows. Depending on when they were made and what raw materials were used, some window panes are rippled like the ocean, and others are bubbled or scattered with bull’s-eyes. Each pane, though, is unique. On the rare occasion when I find a window that’s not salvageable, I always save the glass.

If you’re seeking sources for old glass, check first with salvage contractors in your area or with window-replacement contractors, most of whom will be happy to let you haul away the old sashes that they take out.

Window Frames Rarely Need Fixing

I inspect the window frames as well as the sashes. Like a dentist with a pick, I use a scratch awl to poke around rotted areas to determine the extent of damage. Fortunately, unless the house in question has suffered from serious moisture problems, the frames are almost always rock solid, which is why so many manufacturers have come out with replacement window units that fit within existing frames. If I find some frame rot, it’s usually confined to the end grain where the side jamb meets the sill or to the top portion of the sill itself. These infestations are cleaned out and repaired easily with epoxy.

If serious damage has occurred, it’s most likely to involve the sashes, particularly the lower sash, because they are used and abused the most. If sash rot is minor and localized, I make the repairs in place. But whenever I discover a serious problem such as a severely rotted bottom rail or side jamb, or a broken or rotted muntin strip, I remove that particular sash and make the repair in the shop. Only if the bottom and both sides are missing do I consider a sash to be beyond repair.

Disassembly Requires Care, Especially With Old Glass

As I remove each sash, I hold it up to a light source and take note of which panes of glass are original so that I remember to take special care to save them. Removing old glass without breaking it is a tedious process at best. Sometimes I find that the old glazing putty is so loose that it just needs a good nudge with a paint scraper to get it off; oftentimes, however, the putty is as hard as rock.

Plenty of tools and techniques are available for removing stubborn old glazing putty, and entire house’s worth of windows to repair, I send them to a reputable paint stripper, where the paint can be removed safely. If I have just a few windows to repair, I strip the paint myself using low-temperature heat strippers (photo bottom right, p. 85) or chemicals (Back to Nature Products; 800-423-7733; www.ibacktonature.com).

If the sashes have any minor cases of rot or simple weather damage, they are repaired with epoxy. First, I gently wire-brush the surface free of all loose wood fibers. Next, I carefully warm the wood surface with a heat gun set on its lowest setting. Using a disposable paintbrush, I apply generous amounts of a liquid epoxy (West System; 989-684-7286; www.westsystem.com); the heat treatment allows the liquid epoxy to travel deep into the wood’s fibers, creating a superior bond. As soon as the wood fibers refuse to absorb any more of the liquid, I spread on a fine skim coat of solid epoxy filler to create a smooth finish surface.

Parts And Patches Are Made From The Same Wood As The Sash

Unlike fixed trim elements, a window sash is subject to a great deal of mechanical stress. To ensure that my repairs last as long as possible, I don’t depend on epoxy to fill large gaps; instead, I fashion all but the smallest patches from wood. I rely on a dutchman (a patch that is made with wood) glued with an epoxy adhesive from West Systems to repair damage that would require more than a skim coat of filler (photos below).

When I have to replace an entire sash part, such as a rail or a muntin strip, I first try to scrounge up a match in a local salvage yard. But if that doesn’t pan out, I can replicate the profile using a molding head cutter that fits my tablesaw. (To find out how to make a custom molding cutter, visit our Web site at www.finehomebuilding.com.) If just a portion of the original piece is damaged, I cut back to sound wood and splice new wood to old.

Whether it’s a small dutchman or an entire bottom rail, every replacement part should be fashioned of the same species of wood as the sash: first-growth, tight vertical grain, if possible. I maintain a ready stock of raw material for replacement parts because I never discard any old wood.

Whenever large-scale repairs are needed, the sash has to be disassembled. Early sashes (150 years old or more) were joined by a tapered wooden peg driven through a mortise and tenon. To disassemble this type of frame, the pegs must be punched out from the small-diameter side. Don’t worry about saving the pegs; they can’t be reused. Sashes made in later years substituted glue for pegs; they usually can be separated by cutting through the glueline with a knife, then gently tapping the mortised section loose using a block of wood and a mallet.

After I’ve completed all necessary repairs, I reassemble the window sash using an exterior-grade carpenter’s glue such as Titebond II (Franklin International; 800-347-4583; www.titebond.com). Unlike an epoxy adhesive, carpenter’s glue is reversible, so it allows future carpenters the opportunity to take the window apart should they ever need to make repairs. If the joints are loose, however, I have no choice but to use a thickened epoxy adhesive to fill the gaps.

During the gluing process, the frame is squared up, then clamped tightly and allowed to set for at least 24 hours. Afterward, all surfaces are sanded thoroughly to prepare them for paint: I use 60-grit paper to knock down the high spots, followed by 100 grit to polish everything paint-grade smooth.

Preservative And Primer Ensure That The Paint Stays Stuck

Old wood presents a finishing challenge because it tends to be extremely dry. If left untreated, it will absorb the chemical binders from primer, causing early paint failure. To put some natural resins back into those dried wood fibers, I brush on a generous coating of a homemade wood preservative, a mixture of 50% mineral spirits and 50% boiled linseed oil (photo top left). I let the frame dry for 48 hours before priming it, but I don’t use just any primer.

Traditional primers (oil or latex) soak into the wood fibers to create a bond, but they cannot soak into the epoxy patches and thus are liable to fail. Instead, I apply a coat of B-I-N primer-sealer (Zinsser Co. Inc.; 732-469-8100; www.zinsser.com) over all surfaces (photo bottom left). This product is a white shellac designed to seal knotholes, among other things (see article pp. 60-63), but it forms a strong surface bond that adheres equally as well to epoxy as to wood fibers.

Bed The Glass In A Bead Of Caulk

Prior to reinstallation, I thoroughly clean all the original glass. Then I apply a fine bead of latex caulk to the shoulder that will receive the glass (photo above). I “back-putty” the glass in caulk rather than glazing compound because the supple caulk provides a cushion that lessens the chance that the fragile, old glass might shatter as I’m pressing it into place. After all the panes are bedded in the sash, a few glazier’s points are installed to secure the glass until the caulk has cured.

The glazing process requires finesse and a steady hand, both of which take practice to achieve (photos above). Glazing compound does not hold paint well until it has had a couple of weeks to cure. If time allows, I store the sashes in my shop, then apply two full coats of paint before I reinstall them. When painting over the glazing compound, I’ve learned that it’s important to let the paint overlap the glass (about 1 ⁄16 in.); this overlap prevents water from getting behind the glazing, causing early failure.

Repaired window sashes have a greater life expectancy than new window units, but as with anything that’s exposed to nature’s wrath, they still have to be maintained. I urge all my clients to open and close each of their windows at least once a year and to examine their windows thoroughly for signs of rot at least every five years.

Removing Putty And Paint Is The Hard Part

If a window sash needs major repairs, both glass and paint usually have to come off. To get at the glass, I start by hand-scraping the outside of the frame where the wood meets the glazing putty; removing the overlapping paint helps to break the bond between the two materials.​

1.For Putty Removal I depend mostly on a Fein MultiMaster (800-441-9878; www.feinus.com), which is set up with a vibrating scraper. Coming in flat over the glass loosens most of the putty, but it can be slow going. If the putty is rock hard, I attack first with my 33⁄8-in. cordless Makita circular saw, but this process requires a skilled hand. I set the depth of the blade so that it will not touch the glass, then carefully cut alongside the shoulder of the frame. After the saw cut, the remaining putty goes quietly.

2.Once All The Putty Is Gone I slide a scraper along the surface of the glass to remove the old glazier’s points.

3.To Cut Out Any Putty Embedded Between Glass And Wood I run a knife blade along the edge of the glass. Then all it takes is a gentle push up from the bottom side to free the glass.	4.Use An Electric Paint Remover I use an electric paint remover (Warner Tool Products; www.warnertool.com; 877-992-7637) to strip the flat sections of the sash

5. Heat Gun A heat gun in combination with a contoured scraper takes care of the profiles.

Removing The Window Sash

1.Use a utility knife to break the paint seal from the window stop.	2.Remove the window stop using a small pry bar over a stiff-bladed putty knife.

3.Pull out the lower sash.	4.Pierce the sash cord with a small finish nail to prevent sash weights from dropping to the bottom of the weight cavity.

5.To access the upper sash, remove the parting bead by grasping tightly and pulling straight back.

Repair Sash With Old Wood And Epoxy

1.Deep gouges and rot are carved out and squared up with a chisel to make room for a wooden patch (commonly called a dutchman) that’s fastened with an epoxy adhesive	2.After all surfaces have been wetted with liquid epoxy, a thickener is added to the mix, and a generous helping is applied between the dutchman and the sash	3.Cut from the same species of wood as the sash, the dutchman should stand slightly proud of the surrounding surfaces. After the epoxy has cured fully, the patch can be planed and sanded to make the repair invisible.

Old Sashes Need Special Attention Before Painting

After the repairs are done, the sash is treated with a generous coating of a homemade wood preservative: one-half mineral spirits, one-half boiled linseed oil. After two full days’ drying time, a shellac-base primer is applied. This combination of ingredients ensures that the finish coats of paint bond to a stable, uniform surface.

Glazing Takes Practice

1.To prevent breakage, the author beds each pane of glass in a layer of acrylic latex caulk before he secures them with glazier’s points (one point per side is usually enough).	2.With the sash propped up on a homemade easel, he works glazing compound into a 3⁄8-in.-diarope before pressing it into place.

3.After lubricating a putty knife with boiled linseed oil, he tools the glazing compound using an index finger as a guide. Finally, he eliminates minor imperfections in the glazing by wiping downward with a taping knife.

Storm Windows And Weatherstripping Tighten Up Old Windows

By today’s standards, old double-hungs are drafty; but that problem is easy to fix. The most straightforward solution is to add storm windows. Triple-track units are the most common option, but they can be bulky and conspicuous. If you decide to go this route, buy from a high-end manufacturer that offers custom sizing and a wide choice of colors.

For a less conspicuous appearance, I prefer the Historic One-Light (HOL) unit from Allied Window Inc. (800-445-5411; www.alliedwindow.com). This low-profile storm (photo left) is essentially a single-track unit in which upper and lower sashes mount one over the other; screens are available, but they must be stored elsewhere. For restoration purists who’d rather not see any storm window on the outside of a home, this manufacturer also offers a variety of interior storm-window options.

The windows themselves also can be tightened up. The edges of fixed sashes should be caulked, inside and out, to eliminate air infiltration. If you’re willing to remove them from their frames, sashes and stops can be routed and retrofitted with specially designed weatherstripping. Resource Conservation Technology Inc. (410-366-1146; www.conservationtechnology.com) offers a wide variety of weatherstripping, as well as an excellent catalog that doubles as an installation manual.

For more photos and details on restoring window sashes, click the View PDF button below.