How to Replace a Window Pane
Replacing a cracked or broken glass pane is a very common task for the do-it-yourselfer. It isn’t difficult but it does take a great deal of care, not being afraid of being cut by small pieces of glass and patience. A lot of patience.
If you have misgivings about whether or not you are able to complete such a task then have a professional glazier do it for you. But the point of this is to save money and professional glaziers are not cheap!
If you feel that you are up to this task, have the glass pane cut to size where you buy it. Replacing the pane is one thing but cutting it yourself is quite another!
Types of Glass
You should normally replace the glass with the same type as the broken pane. For most home windows, these measurements would be 5/32 inch (4 mm) glass. Only smaller windows can be glazed with 1/8 inch (3 mm) glass such as interior Georgian door that have several panels. Larger windows require �¼ inch (6mm) or 3/8 inch (10 mm) glass.
Some glass in weak areas such as glazed exterior doors, large panels next to these types of doors, large picture windows and low-level glazed windows must be glazed with safety glass that is either roughened or laminated.
Items Needed
Protective tarp or cloth
Old chisel or glazier’s knife
Thick work gloves to prevent glass cuts
Safety glasses
Mallet
Narrow-blade hook scraper
Tape measure
Flexible putty knife
Wooden matchsticks (if you are leaving the frame in a vertical position)
Tack hammer
Wood primer
Glass
Putty
Glazier’s points
To Begin With.
First remove the window from its frame and lay in down, exterior side up, on a worktop covered with the tarp. Use the chisel to remove the old putty. If your window (or house) is very old, you’ll come across what is referred to as ‘glazier’s points’. They hold the glass in place. In older homes, they may look like metal or wood arrow tips. Remove them with a hook scraper.
Be certain that you are wearing thick gloves and remove the glass from the frame.
Now place on your safety glasses and use a chisel and mallet to remove the remaining large pieces of old putty from the bottom of the rabbets in the frame. Be sure you avoid cutting into the wood. Your mallet can be made of any material from rubber to wood. I bought the cheapest one that I could find!
Using a scraper, clear the thin deposit of putty from the frame rabbets.
Before I go any further, let me explain what a ‘rabbet’ is for the novice homeowner. A ‘rabbet’ is not a furry woodland creature that has been horribly misspelled. This rabbet is a groove cut into the wood frame as a place where your glass pane will lay and be puttied into the frame. All right, enough said. Let us move on.
After you have completely cleaned the area, carefully gather up and get rid of the old broken glass. Give the rabbets a coat of wood primer and measure for the new pane of glass. Provide about 1/8 inch (3mm) clearance on each side for both width and height.
After the primer has dried, check that the new glass is the correct size. Knead the putty in your hands until it’s pliable. Run a long slender strip of the putty about 1/8 -1/4 inch (3-5mm) thick around the bottom of the rabbets. Use the putty knife to press it down flat and smooth it. Trim off any excess that is hanging over the edge.
Now you may insert your glass into the frame. Leave a gap of about 1/8 inch (3mm) all the way around. Gently press the glass firmly into place along its edges. Never, ever press via the center of the glass. Unless, of course, you want to make another trip to the hardware store! Do this until the putty oozes out of the inside of the window. If the window is in place in a vertical position, then place matchsticks across the lowest horizontal rabbet to produce an equal space all around.
Use your new glacier’s points to lock the glass in place. Use your putty knife or the flat part of a tack hammer to press the points into place. NOTE: Do not hit them as if they were nails!
Knead the putty as before and roll it into a thin sausage roll, as before. Begin at one corner and while laying the putty down, push it against the sides of the rabbets. Continue down along the frame until you have completely gone around the entire frame in this fashion.
You must now make a smooth bevel in the putty. Hold your trusty putty knife (handy aren’t they?) at a 45-degree angle with the straight edge on the putty and drag the knife along.
To miter each corner, put the knife diagonally in the center and pull it away from the corner. Use the knife to remove any excess putty left on the glass. The putty needs at least a week to dry before adding creative touches like paint.
Note: Even though you will have to wait at least a week (depending on the weather) to paint, you might want to let the putty set at least an hour or two before reinstalling your frame back into position.
Putty has linseed oil in it. If it has too much, it can be sticky and very difficult to handle. To absorb the excessive oil, roll the putty in a black-and-white section of a newspaper (no colored).
If the putty has dried out, you may add a little linseed oil to it.
If you have putty on the glass, you can clean it up with a little paint thinner. Remember, a little goes a long ways!
The best time of year to replace windowpanes is during the warmer weather. The putty will dry quicker than in the chillier months. And who wants to work on a window frame when it’s cold outside? Brrrr.
SOURCES:
“Repairing Old and Historic Windows: A Manual for Architects and Homeowners” by the New York Landmarks Conservancy
“Caring For Your Old House: A Guide For Owners and Residents” by Judith L. Kitchen
