Glazing putty is something you need when you’re setting a pane of glass into a wood frame. The glazing putty is the adhesive that bonds the glass to the wood and keeps it solid. There is a correct way to use glazing putty; there’s more to it than simply applying the putty and sticking on the glass. Doing it right the first time means you won’t have to do it again.
Step 1 - Preparing the Putty
You can buy glazing putty that applies directly from a tube which is much like caulk and is easier to use than putty from a tub. You need to be able to roll the putty into a thin tube to apply it properly.
If the putty has been sitting for a while, it might have hardened. To soften the glazing putty, you can pop it in the microwave for 20 seconds (set it on full and open the top of the tub. You should only do this is the glazing putty is in a plastic tub). Alternatively, you can mix in a little linseed oil which will soften the glazing putty. Be careful not to use too much.
Step 2 - The Putty Bead
There’s an art to rolling the perfect bead of glazing putty. Roll it out between your thumb and fingers so that it resembles a long, tiny sausage. It needs to be thick enough for the glass to squeeze it out and make a firm, watertight seal. If it’s too thin, it won’t compress properly. If it’s too thick, you’ll need to wipe a lot of it from the glass after application.
Before you apply the glazing putty to the glass, clean the glass fully with glass cleaner. This will ensure a much cleaner bond.
Step 3 - Fixing the Glass
With the glazing putty in place around the edge of the glass, push the glass against the frame. Squeeze down around the edges until the glass in firmly in place and remove any excess putty that has squeezed out from beyond the frame. Use your putty knife for this. When the glass is fully in place, insert the glass points on the outside of the glass. They should be spaced about 6 inches apart and lightly tapped into place with the putty knife. They will fix the glass while you apply glazing putty to the outside. They should not show above the outside of the glazing putty.
Step 4 - Outside
Roll glazing putty into a ball that’s approximately the size of a golf ball. Keep rolling until it’s warm and malleable. Push it into the frame against the glass squeezing it out from corner to corner. To complete the window might take several balls of glazing putty. Don’t worry about how it looks right now.
When you’ve finished, take your putty knife and start in one corner, letting the knife glide over the putty to give a smooth line and also to cut off the excess putty. Press the putty into the frame and smooth with your fingers. Allow to dry for up to 2 weeks before you paint the putty. This will give ample time for it to harden.