Painting old wood windows: sashes, glazing and storm windows

To paint old wood windows so the job lasts, fix the glazing first: replace cracked or missing putty and let it firm up. Then prime bare wood, paint each sash in order, and lap the paint about 1/16 inch onto the glass to seal it. Keep paint thin in the channels and move the sashes while it dries.

Many older homes in Grosse Pointe and across Metro Detroit still have their original wood windows. This guide is about the double-hung kind, though most of it applies to casements too. Our guide to painting older Grosse Pointe homes covers the rest of the house.

How is an old double-hung window put together?

A double-hung window has two sashes, the wood frames that hold the glass. The lower sash slides up on the inside track; the upper sash slides down on the outside one, and a sash lock pulls their meeting rails tight.

Each sash has vertical stiles, horizontal rails and often thin muntins dividing the glass into panes. Each pane sits in a recess called a rabbet on the outside face, held by small metal glazier’s points and sealed with glazing putty.

The sashes ride in channels formed by the blind stop, the parting bead and the interior stop. In many older windows, cords running over pulleys connect them to hidden cast-iron counterweights. Outside, the sill slopes to shed water; inside, the stool forms the ledge.

What does glazing putty do, and why does it fail?

Glazing putty is the beveled bead around each pane on the outside of the sash. It doesn’t hold the glass in; the glazier’s points do. The putty seals the joint between glass and wood and sheds rain away from the sash.

Traditional putty is made with linseed oil. Over years of sun and frost the oil dries out, and the putty shrinks, cracks and falls out in chunks, often first along the bottom of each pane and on the sunniest sides of the house.

Once there’s a gap, rain runs straight in. It soaks the rabbet and the end grain at the sash corners, paint lifts from behind, and the bottom rail and sill start to rot. Michigan’s freeze–thaw cycles speed it along: water that freezes in a crack expands and pries it wider.

It’s time to reglaze when putty is cracked through, missing in sections or loose enough to lift with a fingernail, or when a pane rattles as you tap it.

Should you reglaze before painting?

Yes, wherever the putty has failed. Paint over cracked glazing hides the cracks for a season, if that, and water that gets behind it lifts the new paint with the old. It’s one reason windows are often the slowest part of an exterior painting job on an older house.

Sound putty that’s still tight to glass and wood can stay; prying it out risks cracking old glass that can be hard to replace. Where it has failed:

1. Remove the loose putty with hand tools, without gouging the wood or levering against the glass.
2. Clean the rabbet and add glazier’s points wherever the glass is loose.
3. Prime the bare wood. Raw wood can draw oil out of fresh putty and shorten its life. Use the primer the putty’s label calls for.
4. Press in and tool new putty to a smooth bevel, kept low enough that it can’t be seen from inside.
5. Let it firm up. Some putties need days or longer before painting; others are ready sooner. Follow the label.

Then paint promptly. Paint is what protects putty from sun and weather, so new glazing shouldn’t sit bare for months.

In what order should you paint a window sash?

A set order covers every surface, including the parts that hide when the window is closed. For a double-hung window painted in place:

1. Swap the sashes. Raise the lower sash and lower the upper one until they nearly trade places, then paint the exposed bottom of the upper sash, meeting rail included.
2. Move them almost home. Return both sashes nearly to their usual positions, a few inches open. Finish the upper sash, then paint the lower one.
3. Paint the frame. Do the casing and stops, keep the channels lean, and finish with the sill outside, or the stool and apron inside.

On each sash, paint the muntins first, then the rails, then the stiles, brushing along the grain. Long strokes down each stile leave crisp lines where the parts meet.

Sealing the paint to the glass

Where paint meets glass, it should lap about 1/16 inch onto the pane. That thin line seals the joint between putty and glass so rain can’t work in behind the glazing. Stop short and the joint stays open; go farther and it just looks sloppy.

Practiced painters cut the line freehand with an angled sash brush; others paint slightly over and trim the excess with a razor scraper once it’s dry. Don’t scrape the glass clean to the putty, though, or the seal goes with it.

Inside the house

Inside, window trim takes hands, sun and winter condensation, so a durable satin or semi-gloss enamel is the usual choice. Wipe up condensation before it soaks the bottom rail and stool.

Older interior trim is often coated in oil-based paint, which latex won’t grip without the right prep. Our prep guide explains a simple test, and our guide to painting interior trim and doors covers the rest of the woodwork.

How do you keep windows from being painted shut?

Windows get painted shut two ways: wet paint bridges the gap between sash and stop and dries like glue, or coats build up in the channels until the sash binds. To prevent both:

• Keep the channels lean. The jamb surfaces the sashes slide against, including both faces of the parting bead, need a thin coat at most, and so do the sash edges that ride in them.
• Don’t paint cords or pulleys. Paint stiffens sash cord, which can then crack and break, and a painted pulley can stop turning.
• Move the sashes as the paint dries. Once it’s dry to the touch, slide each sash up and down a few times, and repeat now and then until it hardens.
• Don’t lock them tight right away. Paint that feels dry can stay soft for days, especially in cool or humid weather, and painted surfaces pressed together can stick. Our guide to dry time versus cure time explains why.

Once the paint has cured, a little paraffin wax rubbed on the channels helps the sashes glide.

What should you know about storm windows?

Many older homes have storm windows over the original sashes, either traditional wooden storms or aluminum combination units with built-in screens. A good storm shields the sash and its glazing from the worst weather.

Aluminum combination storms usually have small weep holes or slots along the bottom of the frame that let rain and condensation drain out. Never paint or caulk them shut. If a storm is caulked to the casing, leave the bottom edge open for the same reason, or water can pool on the sill and rot it.

Wooden storms need what the sashes need: sound glazing and paint on every face, edges included. Aluminum frames can be painted after a thorough cleaning and a primer labeled for aluminum, but keep paint out of the tracks where the glass and screen panels slide.

Do old windows have lead paint?

Old windows are a common place to find it. Homes built before 1978 may contain lead-based paint, and windows often carry many layers. They’re also what lead-safety guidance calls “friction surfaces”: each time a sash slides, it rubs the jamb and stops, which can wear old paint into fine dust that settles on the stool and sill.

Window prep disturbs old paint too: scraping putty, sanding sashes and freeing stuck windows all make chips and dust.

The EPA’s Renovation, Repair and Painting (RRP) rule requires certified firms and lead-safe work practices for paid work that disturbs painted surfaces in pre-1978 homes: more than 6 square feet per room inside, or more than 20 square feet outside. Its small-job exception doesn’t apply to window replacement. See the EPA’s RRP program page and our guide to lead paint in older homes.

Should you repair or replace old wood windows?

There’s no single right answer, and it isn’t only a painting question. Weigh these:

• Condition. Failed glazing and peeling paint are maintenance. Small soft spots can often be rebuilt with epoxy, but rot through a sill or bottom rail calls for carpentry.
• Comfort. Weatherstripping and a tight storm improve an old single-pane sash; new units bring insulated glass.
• Character. Original sashes, old glass and period profiles shape how a house looks, and replacements vary in how closely they match.
• Upkeep. Wood windows need paint and glazing attention on a regular cycle; most replacement windows need less.

If the originals stay, the rules above keep them working: sound glazing, sealed paint, open weep holes and sashes that move.

Questions

Painting an older home in the Pointes?Plaster, original trim and old windows need a careful approach. Here’s ours.→