First step is to get the right putty. the latex based stuff you can find at a home center is garbage and wont last, and even Dap 33 is not all that great. You want a tub of oil based
Sarco Type M.
http://www.smithrestorationsash.com/glazingputty.html
You also need:
- A good clean putty knife
- Boiled linseed oil
- Turpentine
- penetrol (optional)
- Exterior oil primer
- Latex exterior house paint in whatever sheen and finish color you want to use.
Now this is the process:
1 Remove the glazing points, take out the glass, and remove all traces of old putty. It may all chip out but there could be some stubborn spots you need to scrape. If there are really stubborn spots soak in linseed oil and let it sit a few days to soften.
2. Thoroughly clean the glazing channel. This needs to be down to bare wood.
3. If the glazing is in such bad shape you will probably want to repaint the entire window. Now is the time to remove any failing paint with your favorite method. Dry scraping, heat, or chemical. If you use chemical I can recommend Fanmar Soy Gel. they make a version with a lead neutralizer built in that's great for working with old paint safely.
(note that professional window shops will put the entire sash in a steam chest to remove all paint and glazing putty in one shot. These can be DIY'd if you have a lot of windows to fix)
4. Prep. Mix up the boiled linseed oil and turpentine 50/50 (we call this blopturp), optionally cut with some penetrol. Brush this mix on the glazing channel. This conditions the wood so the putty will bond and not dry too fast.
5. Prime the entire window with exterior oil primer. If you stripped the window to bare wood its recommended to either use 2 coats of primer on the weather side or even better do a linseed oil conidtioning first then oil prime. Oil primer coats need 24 hours drying time.
Do not prime the glass channels you just treated with oil.
Do not prime the sides of the window that run in the tracks if double hung (these stay unpainted so the wood can breathe)
6. Glaze the window glass. This is an art that has to be learned with practice. It helps to have a good stiff putty knife that's clean to a mirror finish. See the video below.
7. Wait 7 days for the putty to set up and skin over.
8. Paint the entire window with exterior latex. the putty would be finish painted directly, no primer! No finish paint on any part of the window that touches the frame.
If you have a lot of windows to work on Id recommend reading John Leeks book "Saving America's Windows" it describes in much better detail how to do this plus covers repairing common damage.
