Reglazing a wood window

 

If you live in an old house, you most likely have some old wood windows, and windows like these need periodic maintenance.  Old wooden windows can last for centuries if properly maintained, but not everybody knows what that entails.  One of the things you need to maintain is the airtight seal between the wood and the glass.

In a traditional wood window, each pane of glass sits on a ledge called a 'rabbet' that's cut into the inside of the window sash.  The glass is then secured to the wood frame by "glazier points", which are flat pieces of metal that are laid flat on the glass, then pressed part-way into the wood frame.  Finally, the joint between the glass and wood is filled with glazing compound, a type of putty specially formulated to create a long-lasting airtight seal and shed water.  Sometimes a thin layer of glazing compound, called a "backbed" is applied to the rabbet before the glass is set into it. Although properly installed glazing compound can last many decades, it does eventually fail and requires replacing.  This page will document how to properly reglaze a wooden window (at least how I do it).  Everybody seems to do it a little bit differently, but I'll try to explain the reasoning why I do it the way I do.  

Reglazing a window isn't a terribly complicted thing (and is certainly very inexpensive), but it does require a little skill to get nice clean results.  If you're a rookie at reglazing, don't feel bad if your first few attempts don't look so great.  Once you practice a bit, you'll be turning out professional quality results in no time!

 

Tools needed

 

To reglaze a window, you'll need the following tools:

 

Getting started

 

Reglazing a wooden sash is easiest if you can remove the sash from the frame and lay it flat on a workbench.  If not, you can still work on the window when it's vertical. Our patient for this lesson will be my kitchen casement windows:

 

 

  As you can see, the glazing is in pretty poor condition, as is the paint itself. The wood itself is still solid, so these windows are prime candidates for a full restoration. This will involve removing the glass and completely stripping the paint off of the windows. You don't necessarily need to go to this extent with your windows...you need to judge their condition and do what's necessary. As these are outswinging casement windows and both sides may be subjected to the weather, I'm going to remove the glass on these so there's fresh glazing compound (and hence a good seal between wood and glass) on both sides.

Before beginning work, put on your HEPA dust mask. Don't waste your money on those cheap nuisance dust masks....they're not going to protect you from the dust you're going to generate, which most likely will contain some amount of lead. HEPA masks/respirators have pink filters on them. Also make sure you wear work clothes and wash them separately when you're done. If working indoors, make sure there's adequate ventiilation to the outside....a box fan in a window is a good idea.

The first thing you need to do is remove the old glazing compound.  In many cases, the old, failed compound may already be falling out.  Remove what you can by hand first, either by just pulling it off or gently prying it loose with your utility knife.  The remaining putty can be removed with a heat gun. You need to protect the glass from the heat, so either buy a heat gun with an appropriate heat deflector, use a wide putty knife to act as a heat shield, or (as seen below) use one of those fabric-like heat shields often used when soldering pipes.  Heat the putty with your heat gun (at a setting of about 600 degrees), and you'll find that it'll soften up after a few seconds.  The fastest way I've found to remove the softened chunks of putty is with a fairly dull 1/2" chisel, with the bevel side riding along the wood. It's sharp enough to get between the sash and the putty and get it out in big chunks, but not sharp enough to do major damage to the wood. If you do find that you're digging into the wood with the tip of the chisel, just raise the tip of the chisel a bit (with the bevel side still riding along the rabbet). Utility knives and putty knives can also be used to remove the putty, but they take a lot more time (and the utility knife can really gouge up the wood).

 

 

 

Here, you can see one of the windows having its glazing removed. Note that each pane of glass has been labeled so I know where it goes once it comes time to reinstall it....don't assume that every piece of glass is uniform in size! Also, the heat gun isn't on right now....I'm just showing how it should be positioned. There's a dustpan-shaped tip on it as well (that can barely be seen in the photo) that's protecting the pane of glass I'm currently working on.

Once you've removed the bulk of the glazing compound, you should be able to see the glazier points. I've seen three basic shapes of points:  triangles, diamonds, and the more modern "M" shaped push points.  Triangles can be removed by gently prying out one of the exposed corners with you putty knife.  Diamonds are best removed by lifting up the exposed point with your chisel (don't put pressure on the glass or you might crack it), then pulling it out of the wood with a pair of needle nose pliers.  Modern push points can be removed by prying the vertical section away from the wood with your utility knife or chisel.  If the points aren't readily visible, then they're hidden under some glazing compound.  Use your utility knife to score the area where the glass and wood meet.  The knife will run over the points, helping you find them.

 

Removing the glass

 

If your window sash is in need of repair (like fixing loose joints or areas of rot), needs all of the paint stripped off, or the glass in this sash seems to crack on its own, then it's best to remove the glass. If the sash is in otherwise good shape, then you don' t really need to do this unless you want to.

Once all of the glazier points have been removed, the glass is in a position to be removed.  Make sure you've labeled each pane of glass so you know both where it came from and what its original orientation was.

Make sure all of the glazing compound between the glass and wood has been removed. Using your utility knife and scoring between the edges of the glass and the wood will help loosen things up. Then, while wearing protective gloves, gently tap on the glass from the underside.  It'll eventually work its way loose so it can be removed.  Once the glass is out of the sash, use your small scraper to remove any remaining compound that's still attached to the wood, and give it a quick sanding with your sandpaper (wrapping the paper around a small piece of scrap wood helps).  What you want to do is to get down to clean, bare wood:

 

 

 

Once all of the glass is out, you're in a good position to do whatever repairs need to be made to the wood, or to strip the paint off of the sash for repainting.  The same heat gun you used to remove the compound will also remove the paint in short order.  However, make sure the heat gun is set to a temperature less than 1100 degrees F.  There's likely lead paint on that sash, and lead atomizes at ~1100 degrees. The same ~600 degree setting I use for removing the glazing compound works great on the paint, too.

 

Priming the rabbet

 

After the sash has been repaired/stripped/whatever, the first thing you need to do is to prepare the rabbet. The wood sash has dried out over the years, and glazing compound contains a lot of oil.  If you don't treat the rabbet with something, the wood will suck the oil out of the compound, causing it to fail prematurely.  However, there are a lot of differing opinions as to what should be used. Some use oil-based primer, some people suggest using a mixture of linseed oil and alcohol (or just plain linseed oil itself) to "rejuventate" the wood, and others use wood preservatives. I use oil primer for two reasons. First, most manufacturers of glazing compound indicate that you should use it. The second is the fact that it's the only stuff specifically designed to seal wood and prevent it from sucking the oil out of the compound. The stuff I use (Muralo X200 alkyd primer) has linseed oil in it, so I figure I'm pretty well set no matter who's right. In any case, after sanding the rabbets to good bare wood and removing the dust, apply the oil primer and allow it to dry 24-48 hours.

Now is a good time to take a few minutes to remove any old compound or paint that's stuck on the glass.  A flat razor blade (sometimes called a window scraper) works best for me.  

 

 

 

Some people advocate applying linseed oil to the remaining bits of compound and letting that soak in for 24 hours before trying to remove it, but I've found that to be unnecessary. Just make sure the blade in your window scraper is good and sharp. Once all of the old glazing compound and paint has been removed from the glass, use glass cleaner to clean about 2" in from the edges of the glass (cleaning the entire pane at this point is a waste of time....it's gonna get dirty again in short order). Clean both sides of the glass (or just the top side of the glass if you didn't remove it).  

 

Preparing the glazing compound

 

Glazing compound usually comes in quart or gallon cans.  The two brands that seem to be the most popular are Dap 33 Glazing Compound and Sherwin-Williams 66 Glazing Compound.  I've used both, and prefer the Sherwin-Williams product.  The Dap compound doesn't stick to my hands as much as the SW stuff, but I've found that it also doesn't seem to adhere to the primed wooden sash as well as the SW stuff.  Although the inconvenience of the SW stickiness may be a little annoying, if it means that the glazing job will last years longer, it's worth the trouble.  Some manufacturers now sell compound in tubes or as coils of preformed ropes, but I've never had any interest in trying them out. The "old" method of doing it is tried-and-true, so that's what I stay with.

Once you've purchased your can of compound, the first thing you're going to do is to scoop it ALL out of the can and onto a sheet of glass.  The compound has lots of oil in it that tends to separate out as the can sits on the shelf.  Removing all of the compound and kneeding it on the glass will redisperse the oil.  When done, just put it back in the can.

While reglazing a window, your hands WILL get sticky with compound.  A paper towel with paint thinner on it will remove the compound quite nicely.  Keep the towel handy, as you'll probably want to do this a few times during your reglazing session.

 

Backbedding

 

If you removed the glass from the sash, at this point you'll want to reinstall it. Place a small amount of glazing compound (called a "backbed") evenly around the rabbet that the glass actually sits on, then press the glass into the bed of compound so that it smooshes out a bit.  Do this GENTLY and EVENLY around the perimeter so you don't break the glass. Aside from the fact that backbedding improves the seal between the glass and the wood, it also can help make up for any unevenness in the sash that can cause glass panes to crack due to stress.

 

 

 

In this photo, the backbedding glazing has been put on the rabbet, and the glass has been reinstalled. And yes, two panes are missing their labels because I broke the originals and had to buy replacements. No matter how careful you are, sometimes this happens. The replacements cost a whole $1.49 each from my local hardware store.

 

Glazier points

 

At this point you'll want to install new glazier points to secure the glass to the sash. Install the glazier points about 8" apart.  Modern glazier points can be installed with your putty knife, but be careful when doing this.  Don't apply pressure down onto the glass, only sideways into the wood.  The glazier point needs to go straight into the wood, not angled downward so it's putting pressure on the edge of the glass. If this happens, you run the risk of cracking the glass.

 

 

  The same sashes a few minutes later, after the glazier points have been installed. Note that there are 6 per pane....these panes aren't all that big (8" x 10").

 

 

Glazing compound

 When the glazier points are in, it's now time to apply the compound.  Grab a ball of compound and roll it around in your hands for a minute to soften it up. As for how to apply the compound to the glass, there are different ways of doing it. Some people like to roll the compound into a long "snake" and lay it on the glass. I prefer to take a clump of it in my hand, and using the edge of my index finger and the upper edge of the rabbet, "shear" a wad of it onto the glass. Whatever works for you.

 

 

This is what it looks like before smoothing the compound to its final shape. I've applied compound to the muntin bars first so that I can smooth both sides at the same time. If I applied/smoothed compound to one side of a muntin first and then tried to shear compound onto the other side, I'd risk damaging the already smoothed side. Once you shear the compound onto the glass, press it firmly into place with your fingers.

At this point, it's time to smooth the compound. Getting the compound nice and smooth is an acquired skill....it takes some practice to get good at it. The key to doing it right is realizing that the edge of the compound that's on the glass needs to be even with the edge of the rabbet that's on the bottom side of the glass. If the compound sticks out too far onto the glass, you'll see it from the other side of the window. In cross-section, this is what you're aiming for (and my apologies for my pathetic computer drawings):

 

 

 

 

First, wipe down your knife blade with some mineral spirits to help clean and lubricate it. Now, start in one corner of the window, with one corner of the knife resting on the glass, and the opposite side of the knife resting in the upper corner of the rabbbet (the red line indicates the edge of your putty knife):

 

 

 

Now, holding the knife in this orientation and tilting the handle towards the direction of movement, draw the knife down the side. You should have one hand on the knife's handle, and the forefinger of you other hand applying modest pressure to the blade of the knife. This will help to keep the glazing compound firmly fixed into place while you smooth it.

 

 

 

When the corner of the knife that's on the glass reaches the opposite inside corner of the compound, stop. Now, with the knife's orientation unchanged, pull the knife out of the corner in the direction of the arrow. The goal is to bring the corner of the knife that was touching the glass up to the upper corner of the rabbet, defining the 45 degree "bend" in the compound. This step is the hardest one to master.

 

 

 

Follow this procedure for all 4 sides. The last corner you do will end up looking a little messy....just use your knife to smooth things out. Remove any excess compound from the glass, and use it on your next pane (or put it back in the can). If there are any divots in the compound, fill them in with more compound and smooth themout with your knife. Finally, run your finger over the compound....the heat from your fingers will give it a nice, smooth finish.

 

Voila! You've reglazed your window!

 

 

 

The windows, restored and ready for another 80 years of service

 

At this point, we need to let the new glazing compound develop a "skin" before we can prime and paint it. I prefer to paint the rest of the window, then come back later and prime/paint the glazing compound. The compound itself will never fully harden, as it's formulated to stay a little soft and flexible so it can endure temperature changes.  It can take weeks or months for the compound to develop its 'skin', depending on temperature and humidity.  I've found that the compound skins over fastest when it's outside (takes 2-3 weeks), so I just reinstall the windows, wait a month, then prime and paint the compound.  I also wait until this point to clean any residue off of the glass.  If you like, check the manufacturer's specs to see what kind of primer they recommend for the compound...I use a high quality latex primer and paint, and haven't had any problems so far. I use an artist's brush to prime & paint the compound, making sure to extend the paint 1/16" onto the glass....this helps seal the joint between the glazing compound and the glass.