Continuing our focus on window restoration to mark the release of my new book Old Windows Made Easy, I decided to post about putty glazing today. This skill is one of the most important and difficult to get right. Proper glazing makes for long lasting, well-sealed windows.
The good news is that it doesn’t need to be perfect, just done well enough so that it sheds water and seals the glass properly. The nice thing about putty glazing is that if you don’t like the results the first time, you can scrape it off and try, try again until you’re satisfied.
The following is almost an exact excerpt from the book. If you want the complete step-by-step guide for restoring your wood windows, get your copy of Old Windows Made Easy.
How To Glaze Wood Windows
Old wood windows traditionally have glazing putty on the exterior of the sashes. This beveled putty glazing is the big finish to all the restoration work and is typically the last thing done before finish painting.
You can work the putty until you are satisfied with the results. A well glazed window should have clean straight lines of putty and none of it should be visible to occupants from the inside.
Step #1 Bed Glass
Bedding the glass refers to installing the glass back into the sash in a bed of putty. This helps air seal the glass and prevents water from getting behind the glass due to condensation.
Insert the glass into the opening gently and apply firm pressure around the edges. This will cause excess putty to squeeze out the inside.
Once you have the glass, in insert your glazing points (I prefer the diamond points because they are easier to hide behind the putty line). Make sure they are firmly in place and the glass is where you want it to be before setting your points.
Make sure the glass is evenly set into the puttied glazing rabbet and you only leave a thin film of putty on the interior side of the glass.
- Dry fit glass into sash to determine the correct orientation. Trim glass if needed.
- Bed a small amount of Sarco Type-M (or similar) putty in glazing rabbets and gently press glass into bedding. Only press the glass around the edges, especially on large pieces. Pressing on the center of the glass can stress it too much and cause it to break.
- Use a point driver or putty knife to insert at least one glazing point into each side of glass and an additional point every 12″. (Be sure to set point far enough back so that it lays behind the glazing rabbet.)
- Remove excess putty from inside of sash and tool interior putty flush and smooth with profile.
Step #2 Finish Glaze
Properly installed finish glazing putty should be installed at a 45° angle with mitered corners to allow it to shed water effectively. I won’t lie that this can take some practice to get just right. But perfectly glazed windows are not necessary for the putty to do its work.
When you first get your putty out, mix it thoroughly to ensure the oils are spread throughout the whole batch of putty. If the putty is cold, you can knead it a bit to help it gain some workability. My preferred putty is Sarco MultiGlaze but other forms are acceptable like DAP 33 which is readily available at most hardware stores.
In #5 below I mention using whiting. This is simply ground up chalk and it helps to absorb excess oils from the putty and clean the oil residue that inevitably gets on the glass. You can usually find it at paint stores or online.
- Place putty into glazing rabbet.
- Pack putty firmly in the glazing rabbet and glass junction to get a good seal.
- Using a putty knife tool, finish glazing at a 45° angle to smooth finish with clean mitered corners.
- Remove excess putty.
- Using an old paint brush, apply whiting to inside and outside of glass. Work in thoroughly to remove oil spots from glass being careful not to disturb putty. Blow off remaining whiting.
Once your windows have been glazed, the putty will need some time to skin over before painting. Some putties require weeks before being ready for paint while others require only a few hours.
It depends on the putty and the paint type. Always check the manufacturer’s recommendations for the putty you are using and keep in mind that weather conditions will also cause curing time to vary.
One last note: ALWAYS paint your putty! Putty will last for decades if kept properly painted. If not painted, you only have a few months before mildew and dried out putty will make you start all over again.
If you liked this you can also view my video on gazing wood windows at How To: Reglaze Your Old Windows (Video Tutorial).