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Repairing wood windows

The Old House Web

Text: Kendall Holmes
Photos: Deb Holmes

While the repair of old windows may not be one of my favorite jobs, it's not one I dislike -- and that's a good thing, as our home's 50- plus windows were all in need of attention when we bought the place.

Previous owners had neglected routine upkeep, such as paint and putty. Many windows had broken sash cords as well. And and a fair number of them had cracked panes of glass.

Equally bad -- especially given our home's location in chilly central Maine -- those previous owners had fallen out of the habit of hanging our home's wooden storm windows each fall. Instead, they had installed a few aluminum storms here and there.

But for the most part, they simply relied on drafty single-pane wood windows (and huge volumes of heating oil) to try to keep out the long winter's chill.

Needless to say, I've gotten plenty of experience in repairing old windows.

In this story, I'll take you through the process of repairing a wooden storm window which has peeling paint and broken glass. Most of what I'll show you here also applies to repairing a neglected sash from a double-hung window.

The window I'll be working on was among a stack of battered storms that were in our barn when we purchased the house. All of the glass in the window was broken, and the window frame itself was weathered and worn. My first impulse was to toss this window, and replace it with an aluminum storm. But as I poked around, I could see that the wood was still firm -- and that it would clean up just fine.

And so, with three or four hours of work spread out over several evenings -- and for an investment of about $50 in supplies -- I was able to bring this window back from its grave. In its restored condition, it should last many decades, providing that future owners take care of it.

So let's get started.

Materials you'll need

Here are the tools and supplies you'll want to have on hand for this project:

  • A tape measure, to measure the size glass you'll need;
  • Work gloves, to protect your hands while removing old glass;
  • Goggles or safety glasses, to protect your eyes;
  • A wide, flat-head screwdriver;
  • A sharp, 3/4" chisel;
  • A paint scraper, plus a file to keep it sharp;
  • A stiff putty knife;
  • Glazing compound;
  • Glazing points, also known as push points (These are small metal fasteners used to hold window glass in place.);
  • A paint brush;
  • Exterior primer and exterior trim paint.

You'll also need window glass - but more on that in a minute.

And if the window you'll be working on has any loose paint, you should wear a quality dust mask or respirator when scraping, to keep lead dust out of your lungs.

First steps

If you've never repaired a wood window before, here a couple of things you should know before you start:

  • Window glass is held in place by glazing points, or push points. They're usually spaced every six to eight inches where the glass meets the window frame.
  • Putty - also known as glazing compound - is then used to seal the joint between glass and wood. It keeps the rain and drafts out.
  • Broken glass can give you a nasty cut. So you need to work carefully!

Removing broken glass is the first step this project.

If only a few small pieces of glass remain in pane you're trying to replace, you may be able to put on work gloves and goggles and then wiggle out the broken glass. More often, though, you'll need to remove the old putty and push points before removing the glass.

To do so:

  1. Use a chisel, a paint scraper or a putty knife (or combinations of these tools) to remove the old putty. Putty usually fails first where it meets the wood - rather than where it meets the glass. So concentrate on loosening the old putty where it meets the wood.
  2. When you encounter putty that is still firmly attached to both the glass and the frame, you may need to use a chisel to get it out. Try to be careful not to gouge the wood frame.
  3. Every six or eight inches, you'll encounter a push point. Loosen these by wiggling them with a putty knife or chisel, and then pull them out. Make sure you remove all of them ... otherwise the glass won't come out.
  4. Once you've removed all broken glass and push points, continue working on the opening with a scraper (or chisel, if needed) to remove any remaining putty. Your goal is to expose all of the wood below. Should you encounter pieces of putty that won't yield to a scraper, use a piece of medium-grit sandpaper to sand the old putty away.

After removing any broken panes of glass, you'll also want to remove any loose putty from any intact panes of glass. Use a chisel or a scraper for this -- and be sure to use a light touch. Otherwise you'll have even more broken glass to deal with.

Prime time

A properly applied and maintained bead of window putty can last for decades, while a poorly applied bead will fail in a few weeks or months.

What's the difference? Prepwork. In order for this job to succeed, you need to prepare the window so that the right substances (paint and caulk) will stick to the right surfaces.

Putty, it seems, adheres nicely to glass, and it adheres well to painted wood. But it doesn't form a decent bond with bare wood. So before you replace any window glass, you'll need to prime any bare wood.

Primer, for its part, adheres just fine to bright, clean wood as well as to old paint that is not peeling or flaking.

What this means is that before going further, you'll need to scrape and then sand the wood on your window, to remove all loose paint as well as all weathered wood.

Once you've removed all loose paint and weathered wood, you're now ready to paint the window with primer.

Some experts insist you should use oil-based wood primer on old wood, while others swear by water-based primers. I've used both and can't say I've noticed any difference in performance or longevity. In this case, I used a water-based wood primer. Why? I was working inside, in my shop, and water-based primers don't smell as bad.

Buying glass

Window glass is readily available at any hardware store and, in my neck of the woods, even at the local Home Depot.

Measure the size of the glass with a tape measure, yardstick or folding rule. (If you're using a tape measure, be sure it doesn't sag ... this can cause you to make a mistake in dimensions.)

Once you've determined the length and width of the opening, measure it again, just to double-check. Now subtract 1/8" from the length of the opening and 1/8" from the width of the opening. -- just enough to allow a bit of clearance on all sides. This is the size of the piece of glass you'll order at the hardware store.

Installing glass

Once the primer on your window frame has dried, you can install the glass.

Start by applying a thin bead of putty -- no thicker than 1/8" or so -- into the groove upon which the glass will rest. This is known as a setting bead. It helps seal out drafts and moisture. Keep the thickness of this glazing compound fairly uniform so the glass does not crack when you press it down into the compound.

Now you can install the glass.

Press it onto the glazing compound and then insert the push points to hold the glass in place. Push points should be installed a couple inches in from each corner, on all four sides. Then place additional points every six or eight inches.

Putty pointers

Straight out of the can, window putty is stiff, lumpy and generally useless stuff. Before using it, soften and mix it by kneading it until it takes on the warmth of your hand and feels just a bit sticky.

Now form it into strings about the thickness of a pencil. Lay a string of compound along one side at a time and push it roughly into place against the glass and wood frame with the tip of a putty knife.

Now comes the part that may take a bit of practice: finishing the putty by "drawing" a smooth, straight line with your putty knife. The trick to this step is to press firmly and move in one long stroke, from one side of the window to the other. Then, once you're done, scrape off any excess compound.

Finishing touches

Finished with the putty? The tough parts of this job are behind you! And I'll bet you'll like this next step: Put the window aside for at least a couple of days (a week is even better) to let the putty form a bit of skin.

After the glazing compound has dried, paint it to finish sealing the seams between the glass and the compound. Even if you're in a hurry, don't forget to paint! Exposed, unpainted window putty will fail in just a few months.

And after your paint dries, clean the window with window cleaner and paper towels (or old newspapers, if you choose) to get rid of fingerprints and dried up putty oil.

Finally, before re-hanging your storm, check the weatherstripping on its back side - the side that will butt against the wood trim on your house. Old-timers used felt or leather for weather stripping - and if the older weatherstripping is intact, so much the better. If not, you'll want to replace it with a modern vinyl tubular weather stripping.

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