How to reglaze a window without putty
Anyone who has scraped grey, crumbling putty out of a window rebate already knows the problem with linseed oil putty. It dries hard, shrinks, cracks, and eventually falls out in lumps. Then water sits in the rebate, and a while after that you are cutting rot out of the sill. Putty also wants weeks of curing before it will take paint, which is a long time to leave a window half done and unprotected.
Our own installers gave up on it years ago in favour of a hybrid polymer glazing compound, and that is the method below.
Why a hybrid polymer instead of putty
Sash Glaze goes on much like putty and then behaves like a high grade sealant. It stays flexible permanently, so it moves with the timber through a Hobart winter and a Melbourne February instead of cracking away from it. It grips hard to both glass and timber, around 300kg per 10cm², which means it holds the pane as well as sealing it. And it is paintable in hours rather than weeks.
It is the highest volume product we sell. Most of those orders are repeat customers, which tells you more than any spec sheet.
Get the old putty and glass out
Soften stubborn linseed putty with a heat gun on a low setting, keeping it moving so you neither crack the glass nor scorch the timber. Work the softened putty out with a hacking knife or an old chisel you do not love. Lift out the glazing points, the small metal triangles pressed into the rebate, and set the pane aside if you are reusing it.
Clean the rebate back to bare, sound timber. If your chisel finds soft spots in there, stop and repair them before you go any further. There is no point sealing a new pane into rotten wood.
Prime any bare timber
Raw wood pulls the oils and solvents out of a fresh bead. A coat of primer, or a thin skim of compound worked into the grain and left to grab, is enough to stop it.
Bed the glass on a back bead
Run a thin bed of Sash Glaze around the rebate and press the pane firmly into it so it squeezes out along the whole line. This bedding layer is the actual seal, and it is what stops water tracking behind the glass and into the joinery. Press the glazing points back in to hold the pane while you work on the front.
Tool the front bead
Lay compound along the front edge of the glass and cut it back to a clean 45 degree bevel with a putty knife. A slightly wet blade gives a smoother finish. Keep the top of the bevel just below the sight line of the glazing bar so that from inside the room you see glass and timber rather than a fat line of sealant.
Let it skin, then paint
Sash Glaze is touch dry quickly and paintable within about a day, which changes how you plan the work. You can glaze on Saturday and paint on Sunday instead of coming back in three weeks. When you do paint, lap a whisker of paint onto the glass itself to close the joint between compound and pane.
There is one more use for it that saves a lot of work. If the old putty is cracked but still firmly stuck, you do not have to strip it out at all. Skim over the top with Sash Glaze to reseal the surface and you buy that window many more years without pulling a single pane. That trick alone is why a lot of trades keep a cartridge in the van.
If you want the longer argument for switching, we set it out in why we stopped using traditional glazing putty.
FAQ
Can I use silicone instead of putty on windows? Plain silicone is a poor choice. Paint will not stick to it and it can trap moisture against the timber. A hybrid polymer glazing compound is made for the job: flexible, paintable and safe on glass.
How long before I can paint new glazing compound? Hours rather than weeks. Sash Glaze is normally paintable within about 24 hours, against several weeks for linseed putty.
Do I still need glazing points? Yes. The points hold the pane mechanically while the compound cures and bonds, and they stay in there afterwards doing their job.
Why does my old window putty keep cracking and falling out? Linseed putty cures hard and brittle, then shrinks. The timber around it keeps moving with the seasons, and the putty has no give left, so it splits at the join and lets go.
Can I put Sash Glaze over existing putty? Yes, as long as the old putty is still firmly attached. Skim over it to reseal the surface rather than stripping the pane out.
What you need for this job
- Sash Glaze Instant Adhesive 290ml. One cartridge does several average panes. Bed the glass, tool the front bead, paint the next day.
A standard caulking gun will run it. If you also plan to fill rot while the pane is out, the epoxy range is the other half of that job.