Repairing Putty Window Glass

Jan 16


John Rocco

John Rocco

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Have you ever thought about fixing a broken window in your house, but didn't think you could do it because nobody ever taught you how to cut glass? Well, you really don't have to know how to cut glass in order to repair your window. If you knew how to remove the frame, you could order a replacement piece of glass from your local glass shop already cut to the proper size. Then, it's just a matter of installing the new glass into the frame. But, there are so many different kinds of window out there, there is no way i could explain them all in one article. So, this is going to be the first in a series of articles describing the repair procedure for each type of window.


There are really two categories of windows out there. They are single pane windows and dual pane windows. Then,Repairing Putty Window Glass Articles within those two categories, there are several types of windows in each category. Let's start with the single pane window category. This would be older windows that were around before the building industry became more energy conscious. It just means that there is a single piece of glass in the frame that surrounds it. A lot of homeowners mistakenly think a horizontal sliding window must be a double pane window, since there is a pane of glass in the sliding panel and another pane in the stationary panel. The terminology refers to the number of panes in the sliding or fixed panel alone. In other words, a single pane horizontal sliding window has a single pane of glass in the sliding panel, and a single pane in the fixed panel. A double pane slider would actually have two pieces of glass in both the sliding panel and fixed panel. The pieces in each panel are separated by approximately 3/8" of air, and have a metal spacer around the edge of the glass.

So, let's get back to the single pane repairs. One of the more common types of single pane windows are the type that uses putty to hold the glass in the frame. All old wood windows are done this way. Old metal casement windows are usually done this way as well. The casement window is the kind with the handle on the inside bottom corner that you crank, and the window opens outward on a top and bottom pivot. Let's focus this article on the putty style replacements.

Before you begin, pick a local glass shop in your area where you will go to pick up the new glass. Make sure they are going to be open the day you do the work, and confirm with them that if you call in an order for a pane of glass in the morning, you can pick it up in an hour or two. You dont want to remove the glass from the window frame, then find out the glass shop won't have your glass cut until next week. If they can't guarantee a two hour turnaround, keep looking.

The fastest and easiest way to remove the old glass is to break it out. Put an old sheet or a tarp on the ground below the window. Then, put on some gloves. Use gloves with a material that will prevent a piece of glass from cutting your hands. A pair of gardening gloves should work fine. Get yourself a pair of safety glasses as well. Trust me, you don't want to get hit in the eye with a piece of flying glass. As my Father always used to tell me, "Better safe than sorry". Now, go inside with a hammer in hand and knock the glass out of the center part of the window. It's best to leave some glass sticking out around the edge. You can grab the protruding glass and use it as leverage to pop the old putty loose. The more old putty that you can get to come out along with the glass, the less scraping you will have to do. I have done some wood window replacements where the putty was dried and cracked, and it practically fell out on it's own. On the flip side, i have done some where the putty had almost become a part of the wood. The only way to separate the putty from the frame in those instances is to use a putty knife to scrape it down to the wood. While removing the putty, you will find little pieces of metal that are used to hold the glass in place while applying the putty. The wood windows use push points, and you can get a package of new ones at the hardware store. If you're working with the metal casement window, the metal clips are called sash clips. You might have a harder time finding these. Frankly, i don't see any problem reusing them.

Once you have all the glass and putty removed, clean the frame with a paint brush. Then measure the width at three spots:bottom, middle, and top. Take the smallest measurement and deduct 1/8" for wood windows and 3/8" for steel casements. Then, measure the height at the left side, center, and right side. Take the smallest measurement and deduct 1/8" on wood windows and 1/4" on casements. When you order your new glass, order double strength glass, and give the width first, then the height. When you get the new glass home, the installation process is slightly different between wood and steel windows. If it's wood, put a thin bead of caulk on the frame where the glass is going to make contact. Install the glass. The caulk will hold the glass in place while you install the push points. You can either apply putty or use white caulk instead. If you're going to use caulk, cut the tip below the tapered part, and cut at a 45 degree angle. You want the largest possible hole to allow the caulk to cover the large area previously covered by the putty. The caulk method is faster than putty, but it requires more skill to make the job look nice. If you have steel casements, the only option is putty. The area is just too large to use caulk. The sash clips install differently than the push points. The push points stick into the wood, but the sash clips insert into small holes in the side of the casement frame. Sometimes the holes get plugged with old putty and it's easy to overlook them. Take your time applying the putty. Make sure you use the putty knife to smooth the surface. You just repaired your putty window. I will be on Christmas vacation for the next two weeks, but when i come back, i will continue this series of articles on repairing single pane windows.