How to Restore Antique Sash Windows: A Step-by-Step Guide

Antique sash windows, with their divided lites and weighted sashes, add character and history to any building. However, they can also be an energy drain compared to modern replacements. If you’re committed to preserving these beautiful windows, this guide offers a detailed, step-by-step approach to restoring them, ensuring they last for generations.

Restoring a window sash, especially one that’s a century old, is a meticulous process. It involves removing old glazing putty and glass, stripping the frame to bare wood, making necessary repairs, priming, reinstalling the glass and glazing, and finally, applying protective coats of paint. While no single step is overly complex, the process requires patience and attention to detail, with significant downtime between stages.

Understanding the Timeline and Necessary Preparations

Before diving in, it’s important to understand the timeline involved. For instance, steaming to soften putty allows for easier glass removal, but it also softens the wood, requiring a 24-hour drying period before scraping. Epoxy repairs need another 24 hours to cure before sanding, and glazing putty requires approximately two weeks before it’s ready for painting. This extended timeframe necessitates a plan for temporarily closing window openings. A secure and convenient method involves using strips of 7/16-inch OSB fit into the parting-bead groove, along with a larger piece to fill the opening, secured with drywall screws.

Safety First: Lead Paint Considerations

If your home was built before 1978, there’s a high probability of lead paint being present on the window sashes. It’s crucial to take appropriate safety measures. The EPA’s Renovation, Repair, and Painting (RRP) program provides detailed guidelines, which are mandatory when working on a client’s home. Even for personal projects, testing for lead paint is recommended. When working with lead paint, always use precautions such as closing off the work area, using a HEPA-filtered shop vacuum, wearing a Tyvek suit, gloves, and a respirator, and misting the sashes to minimize dust. And always prime the sashes with an oil-based primer safely, in a well-ventilated area and with a proper respirator.

Not every old window is salvageable. Sometimes, replacement is the most sensible option. However, if you decide to restore yours, do it right.

Step 1: Removing the Sash with Care

Old weighted-sash wood windows were designed for disassembly and repair. Understanding their construction is crucial. However, avoid assuming parts are interchangeable between windows. Label every piece as you remove it to ensure correct reinstallation.

1. Dent Prevention Cut any paint or caulk between the interior stop and window frame with a utility knife. Then, pry the stop free using a putty knife to protect the frame. If there is a nail near the top miter, cut it with an oscillating multitool before trying to pull out the stop.	2. Remove And Inspect The Cord The sash cord is easy enough to remove, but it’s worth inspecting its condition and, if necessary, replacing it with new sash cord (not rope, which will degrade in sunlight).

3. Upper Sashes Are Often Stuck Though upper sashes are meant to be mobile, they’re often painted shut over the years. Use a pair of bar clamps, reversed to spread apart, to ease the sash free. Place the clamps wide, at the edges of the meeting rail. Otherwise, you may just bend and possibly damage the rail and the pinned bridle joints used to assemble these sashes.

4. The Parting Bead Is Tricky The shape of the upper sash’s meeting rail makes it impossible to remove the parting bead by pulling it to the side. Instead, you have to lower the upper sash all the way. Then, starting at the top, use a pair of sheet-metal pliers to pull the parting bead from the groove. Once most of the parting bead is out of the groove, pull the top end inward so it clears the window frame, and then pull up, tapping the pliers with a mallet if necessary.

Step 2: Steaming the Sash for Glass Removal

A steam box softens the old glazing putty, making glass removal safer.

• Build a Simple Steam Box: A steam box is a helpful tool. The design creates steam by heating water in a metal gas can (that has never held gasoline!) set on a propane-fired turkey fryer. Steam enters the box through a common rubber hose and is distributed evenly inside through copper pipe drilled with holes. The box itself is foil-faced rigid foam seams caulked with fire-rated silicone with a wood frame for durability.

1. Make A Simple Steam Box A steam box is a fairly straightforward and very helpful tool for this job. The box, based on a design by my friend Dave Bowers, creates steam by heating water in a metal gas can (that has never held gasoline!) set on a propane-fired turkey fryer. Steam enters the box through a common rubber hose and is distributed evenly inside through copper pipe drilled through with holes. The box itself is foil-faced rigid foam seams caulked with fire-rated silicone with a wood frame for durability. You can make the steam box the right size for your project and create shelves inside with copper pipe or electrical conduit.

• To prevent thermal shock, either place the sash in the steam box before turning it on, or leave the door ajar for a few minutes to preheat the sash. Place the sash with the outside facing up to prevent the glass from falling out as the putty softens (typically 45 minutes to an hour).

2. Be Ready To Go Stand back when first opening the door and let the steam clear. Wear gloves with thermal protection (like these Therma-Fit gloves from Atlas) and quickly move the sash to a flat work surface.	3. Free The Glass Use a putty knife to scrape away the old glazing. Before attempting to remove the glass, make sure all the glazing points are out of the sash. If the putty knife didn’t get them out, use a screwdriver or pliers to pry or pull them. Finally, lift the glass from underneath and carefully set it aside.

• Clean the Glass: Use glass cleaner and new razor blades. Label each pane of glass, as they are often irregular and will only fit their original openings properly.

| 4. Clean The Glass With the glass removed, you have access to its edges and corners. So, now is a good time to clean it up. Use glass cleaner and new razor blades. Old or jagged blades can scrape the glass, so change blades often. Once clean, label the glass with a piece of tape. The panes tend to be irregular and will likely only properly fit the opening they came from. | |

Step 3: Scraping, Repairing, and Priming the Sash

After steaming, let the sash dry for about 24 hours. Scrape the wood down to bare wood to prepare it for repairs.

• Clean out any rot, paint, dust, or debris from the areas to be repaired. Apply LiquidWood epoxy liberally to the damaged areas, allowing it to penetrate the wood.

1. Clean It Out Use a pick or knife to remove any rot, paint, dust, or other debris from the areas to be repaired and to open up the checks to allow the epoxy to penetrate and fill the repair.	2. Penetration, Not Puddles Brush on the LiquidWood epoxy liberally, but only in the area in need of repair. Wait for it to penetrate the wood. The area should look wet, but there should not be puddles.

• Fill the damaged areas with WoodEpox, and let the epoxy set for about 24 hours. Sand it smooth with an orbital sander to prepare it for primer.

3. Fill The Damaged Areas Mix the WoodEpox and work it into the repairs with a wide putty knife.	4. Sand It Smooth Allow the epoxy to set for about 24 hours and then sand it smooth with an orbital sander. Run the sander over the entire sash at this point to prepare it for primer.

Using the right tools, such as an easel, Bahco scrapers, and Abatron epoxy products, will help get the job done quickly and efficiently.

| 1-in. Bahco Ergonomic Carbide Scraper |
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Drop-Shaped Replacement Blades

| Abatron Epoxy Products |
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Step 4: Reinstalling the Glass

After coating the sash with oil-based primer, it’s time to reinstall the glass, bedding it in glazing putty.

• Knead the putty to an even consistency, mixing in extra chalk as needed to achieve a tacky but workable texture. Apply a thin layer of glazing putty into the glazing rabbet before inserting the glass. Use a palm sander with a soft cloth wrapping the base to vibrate the glass into place. Flip the sash over and scrape away any squeeze-out with a putty knife.

1. Prepare The Putty Knead the putty to an even consistency. Mix in as much additional chalk as necessary to make the putty feel tacky but workable without sticking to your fingers.	2. Bed The Glass Put a thin layer of glazing putty into the glazing rabbet before inserting the glass. Then use a palm sander with a soft cloth wrapping the base to vibrate the glass into place. Flip the sash over and scrape away the squeeze-out with a putty knife.

• Secure the glass using glazing points. If they don’t fully penetrate, tap them in by hand.

3. Install The Points Shoot the glazing points into the sash to secure the glass. If the points don’t penetrate enough to be completely covered by the glazing, or if you don’t have a glazing-point driver, tap them in by hand.

Step 5: Glazing and Finishing

Tool the glazing to slope away from the glass, matching the size of the rabbet.

• Glaze the top of each pane, then both sides, and finally the bottom. Brush the glass with chalk to remove any oil residue from the glazing putty.

1. Upside Down First, glaze the top of each pane.	2. Sideways Next, glaze both sides of each pane.

3. Right-Side Up Finally, glaze the bottom of each pane.	4. Clean The Glass Again Brush the glass with chalk to remove any oil residue from the glazing putty.

Allow the glazing to set for two weeks before painting, and wax the sides of the sash before reinstalling.

Restoring antique sash windows is a time-consuming but rewarding endeavor. By following these steps, you can preserve the beauty and history of your windows while improving their functionality for years to come.