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Glass Replacement - How to Replace A Single-Pane Window or Repair Window Glazing

Cat silhouette in windowWindow pane replacement and glazing is right up there in my top ten fun things to do, next to cleaning the toaster and sorting socks. So, if you catch a little sarcasm, or bitterness, or just benign contempt for the process, don't worry. I'll be all right.

Many home improvement books consider replacing a pane of broken glass a no-brainer!  HUH??????

I can only assume that the writer never tried to replace a pane of glass, or perhaps opted to hire someone like myself or a pro glazier to do the work. It always looks easy when a pro does it!! That's why we get the big bucks (Oh, really?).

Actually, once you get past the danger inherent in the handling of glass, the job really just requires a little patience, some common sense, and a few tools. Eye protection is a must. You can also wear a pair of gloves to protect yourself from the vicious cuts you might get, but they will limit your dexterity. I also put on a long-sleeved shirt, even in hot weather. Little pieces of glass just love to stick to sweaty skin, so swallow your discomfort and protect yourself!

Removing the putty...

The easiest glazing jobs usually fall to contractors, who deal with newly manufactured windows with soft, fresh putty. It doesn't take much more than a stern look for new putty to virtually leap off the sash! Lucky you, with your 30 year old windows, will need a source of heat to soften the putty.

Professional glaziers have a special heating iron to soften the putty. For the occasional reglazing job, a heat gun is the wisest choice. The sash are wooden and can easily burn from the intense heat of a propane torch (the distant #2 choice), especially in an older home where the wood has been drying for years. I've tried using a torch with a soldering head, which is a little safer, but it gets so hot that the paint smokes, making the work more unpleasant. And, besides, you have to watch where the "trailers" of flame from behind the soldering tip shoot out. They can burn things too! Even you!

Homes have been burnt down by plumbers and painters injudiciously using torches, whether for glazing removal or paint stripping.
Do yourself a favor... don't use a propane torch unless you absolutely have to!!

For safety, wear eye protection and use gloves to protect your hands from the heat and the glass. Set the heat gun on a moderate setting, increasing the heat only as you feel is needed. If you use too high of a heat, you can cause the glass to crack in adjacent frames. You may also cause the paint away from the glazing putty to lift off! You will know if the heat setting is too low because the putty will not soften.

Heat a section of putty, and use a 1" stiff-bladed putty knife or wood chisel (this is where having an old dull one comes in handy) to gradually dig out the putty, using a pushing and lifting motion. Continue to heat the putty as you work your way around the frame.

Once you 'break' the surface of the old putty, the remainder of the removal is much easier, because the heat can how get do the wood below. If there are missing sections of putty, then start removal there.

Use heat gun to soften window glazing puttyYou can pry the putty away from the wood, or away from the glass. The wood is soft and can scar easily, so I run the blade against the glass (see graphic) if there is enough glass remaining in the frame to do so. The worst that could happen to the glass is that it could break... only a problem if you are just reputtying instead of replacing the glass.

If the putty is literally falling off the windows, then you may be able to forego use of the heat gun and simply scrape the putty residue out, using a chisel or stiff straight putty knife.

Trying to pound out the putty using a hammer and chisel, or exerting excessive force, can potentially break the glass in adjacent frames, or even break the sash itself. Be judicious in your use of force!

Removing the points...

Glazing pointsAs you work around the window, be aware that there will be glazing points around the window frame under the putty. They are pushed into the wood against the glass to hold the glass in place before the putty is applied. They can be removed as you bump into them or left in place until all the putty is removed. Simply use the putty knife to pry them up.

I would advise you to save the old points and reuse them if possible. Some companies use points that are quite small compared with hardware store generic points, and a taller point may poke through the surface of the new putty as you smooth it. This is especially a problem with the point pictured on the left, which has little tangs on it which restrict how far you can push it in!!

The other potential problem in using different points is if the framework between panes is very thin. Using a larger point (such as the one at the right in the graphic) may cause the frame to crack.

Removing the glass

You will have an easier time removing the pane if it is broken through. I know, it was a real mess, but it is easier to remove smaller pieces from the window frame than one unbroken piece. You will probably find that, even after you remove the putty and the points, the window still won't come out. Recheck your work and be sure that there are no high spots in the remaining putty residue that may be blocking removal of the glass.

At this point, if the glass does not come out with a light tap or two, it may be glued in place by the old putty that was used to "bed" the glass... that is, a small layer of putty that is put around the wood frame before the glass is set in. This bedding gives a better air seal and allows the glass to seat firmly against the frame when you put set the points.

Most of the time, heating the glass with the heat gun (not too hot!!) around the perimeter will sufficiently soften the old putty to allow you to remove the old glass. If this also fails, then you may have to break the glass to remove it.

To keep glass fragments from flying everywhere, use duct tape and cover the inside of the glass. If it's a large pane, duct tape a heavy plastic trash bag before you start breaking it out. Once done, you can use a hammer and nail set to sharply crack the glass into a malleable mass!

To Prime or Not To Prime?

Now, this is the point where most books advise you to lightly sand the areas where the old putty was, and then coat the area with a half & half mix of alcohol and linseed oil or an oil- based primer, or pat your head and rub your stomach at the same time. Do you really have to? Good question? The claim is that if you don't, the oils from the new putty will be absorbed into the dry wood and the putty will not stick properly. My rule or thumb is not to prime unless the puttly is so old and dry that it's falling out. Since the wood has been exposed to the elements, priming should be done.

Of course, the wood should be dry and dust-free. You can also wipe the surface with Wilbond, which is a liquid deglosser. This will further clean the surface for better adhesion of the putty.

However, since the manufacturers of glazing compound prefer that you do a preparatory priming of some kind, so I will leave it up to you... if you don't mind delaying your project for up to 24 hours so that the primer can dry, go for it. There is no harm in waiting.

(NOTE:  If you are using a latex putty instead of linseed oil-based putty, don't use linseed oil as a primer.  Use a quick drying oil or water-based primer sealer instead.)

Install the new glass...

If you are looking for a primer on glass cutting, look elsewhere. Hey, glass cutting was just one of those skills I choose not to perfect. I'm never more than ten minutes away from a hardware store, with all those smiling, happy people with all the glass cutting ability I lack. I could never see the point of carrying a piece of glass around to cut... whenever. Sort of like carrying a potato around to remove broken light bulbs...

Measure exactly for window glassSo, before you make a trip to your hardware store, make careful measurements of the window frame. It is usually a good idea to measure at three points on each side... at each end and at center. Subtract 1/8" from the smaller of the measurements.

NOTE: Some window frames have a slot in the top of certain panes that the glass slides into. You will generally find this on the upper panes of the lower sash of a double hung window. If this is the case for the pane you are replacing, measure the height of the frame and add 1/8". There is no need for the glass to slide all the way into the slot.

Tick tock tick tock... back from the hardware store? Great! Take a minute and clean the glass. I usually give it a good rubdown with denatured alcohol, unless I have a commercial glass cleaner available.

Carefully put the pane of glass into the window frame and make sure it fits. Just another moment of truth, right?

Now it's time to "bed" the glass. No, this is not a cheap soap opera, just getting close to putting this project to sleep. Apply a thin bead of putty to the frame. Then press the glass into it. The idea is to seal the glass against the front of the frame. You should see the putty squeeze between the glass and the frame. If a little squeezes out of the back, that's OK, you can clean it up later.

Once the glass is tight against the frame, insert the points. Follow the same layout as the original. Small panes up to 12" can use 1 or 2 points per side, evenly spaced, adding 1 point for every 6 -8 inches. A 24" square pane would have 3 or 4 points per side. To insert the points, put one against the glass with the point down into the wood. Use your putty knife to wiggle-push the point down until it is seated at a height below the final height of the putty. It takes a knack that you'll get really fast! If you bought points, you may have gotten an insertion tool packaged with them. Use it if it seems like it will help you. If you use this tool, you can use a hammer instead of the putty knife, but be careful doing any whacking near the glass!

NOTE: I mentioned above certain windows that have panes which are slotted on the top to allow you to insert the glass. You do not need to use points on the slotted edge! Instead, when puttying, press putty into the crack to secure the glass, and use points on the other three sides.

Check to be sure the glass is securely pressed against the front of the frame on all sides. If so... the final act!

Putty me like you own me...

As you've probably come to realize, glazing is a real test of your ability to control your wildest impulses... like to drive your hammer through the window and take a trip to the coast for 3 or 4 years. Finesse this and finesse that! Well, the whole project now rests on how you do the reputtying. Because this is what everyone will see. Everything before it is meaningless if you mess up now. Really makes the last two hours feel wasted, doesn't it?

First things first. Do not purchase a latex-based putty in a caulking tube. Get the real thing, which is an linseed oil-based product in a can. Some painters use caulk tube glazing compound to save time because it dries faster, allowing you to paint over it more quickly.  My experience with this product has not been positive.  It doesn't produce the smooth surface you can get from a quality linseed-oil glazing putty and makes a mess if you try to smooth out the bead with a tool.   Just my opinion, of course, so it's your dime!  Spend it wisely.

Chisel angle for removing glazing puttyRemove a golf ball sized piece and warm it by rolling it in your hands. Then, press it into the frame against the glass, so that the groove is overfilled. Neatness doesn't count here. Once you have done all four sides, pick up your putty knife and, starting in any corner, glide the knife over the putty, pressing it firmly into the frame and cutting off the excess putty at the same time. Move slowly, with the knife at a deep angle to the frame (see graphic). Once you've worked your way around the entire frame, you can fuss to your heart's content to get your putty angled properly and smooth as a baby's behind. Feel free to use your fingers for smoothing, if necessary.

After you are satisfied with your work, be sure to remove all the excess putty from the glass, and wipe it down with mineral spirits (good old paint thinner) to remove the oils from the putty. If you want to be real fussy, you can do a absolutely final wipe with denatured alcohol, which will leave the glass sparkling clean. Just keep the alcohol away from the putty as best you can.

Having problems with double-pane insulated glass? See more complete info on insulated glass on our Insulated Glass Page!

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Jerry Alonzy, the founder of Naturalhandyman.com

Written by Jerry Alonzy

Jerry Alonzy, a.k.a. the Natural Handyman, has been an active handyman for over 30 years with experience in most areas of home repair and renovation.

As a do-it-yourself author and web developer since 1995, he has been featured in USA Today, the Today Show and on radio shows, magazines, newspapers and websites. His material appears widely on the web, but primarily on his website... The Natural Handyman. You can also find him on Google+.