Putty glazing for steel windows

What putty glazing is

In a steel window, the glass sits against a narrow ledge in the frame called the rebate. Linseed oil putty, a soft paste that hardens slowly, is used to bed the glass into that rebate and to seal it on the outside with a neat, angled bevel. Small metal clips or pins, often called sprigs, hold the pane tight against the frame while the putty does its work. Our quote form lists this frame type as "Steel frame (putty)".

When it is fresh, putty keeps water out and holds the pane firmly. After many years of Highveld sun, it dries, cracks and eventually falls away in chunks. That is when panes start to rattle, water seeps in behind the glass and the steel underneath begins to rust.

Why older steel windows need it

Plenty of Gauteng homes built decades ago still have their original steel windows, and many of them are in good shape apart from the glazing. Reglazing with fresh putty is usually all it takes to make them sound and weathertight again. Steel windows are also common in older flats, where replacing a whole frame is rarely an option.

How the job is done

The old putty comes out first, along with any broken glass, and it has to be removed completely. That means chipping and scraping the rebate clean without damaging the steel. Any loose rust is cleaned off so the new putty has something solid to grip.

Next, a thin layer of bedding putty goes into the rebate and the new pane is pressed into it, so the glass is cushioned rather than sitting on bare metal. Sprigs are fitted to hold the pane in place. Then the facing putty is worked into the corner between glass and frame and smoothed into a clean bevel, and any excess is trimmed from the inside.

After we leave

Linseed putty needs time to form a skin before it is painted, usually a couple of weeks depending on the weather. Painting it once it has cured protects it and helps it last. Paint should run slightly onto the glass to seal the edge of the putty against rain.

Glass for steel windows

Most steel windows take 4mm float glass, which our mobile teams carry. For bigger panes you may prefer 6.38mm laminated shatterproof glass. If your window has patterned or wired glass that we do not have on the van, we source it and can cover the opening until it is ready.