Painting steel casement and leaded windows: rust, glazing, hardware and when to call a specialist

Steel casement windows are painted by removing loose paint and rust back to sound metal, priming bare steel with a rust-inhibiting primer, sealing the joint where glass meets the frame, and applying thin finish coats made for metal. Hardware is masked and moving edges are kept clear so the windows still open. Leaded and divided-light glass is cleaned gently and never washed with force.

Steel casements and leaded or divided-light windows are among the most recognizable features of the 1920s–40s houses found across Grosse Pointe and Metro Detroit. Tudor Revival and French-inspired houses often have them, along with some Colonial Revival homes. They’re also among the most demanding surfaces a painter handles. Here is how the work is done carefully, and which problems need a specialist rather than a paintbrush.

Why are steel casement windows harder to paint than wood?

Steel does one thing wood doesn’t: it rusts, and rust spreads under paint. A small break in the coating lets moisture in, rust forms underneath, and the paint lifts in bubbles and flakes. Michigan’s freeze–thaw cycles, humid summers and winter condensation on cold steel give rust plenty of chances.

The profile is demanding, too. Casement frames are slim, with narrow bars, corners, hinge pivots and a joint at every pane. There is little surface to work with and a great deal of edge. Edges are where paint thins and fails first, so a careful painter builds the coating deliberately instead of relying on one heavy coat.

And unlike a fixed window, a casement is meant to move. The paint has to protect the metal without gluing the sash to the frame, which is a problem wood windows share but steel makes harder, because rust and paint together can lock a hinge solid. Our guide to painting old wood windows covers the wood side of the same problem.

How is rust dealt with before painting?

Rust is not covered, it is removed. The usual steps are:

1. Look first. Check the bottom rail, the corners and the glass edges, where water collects. Surface rust looks like orange dust or light pitting. Deep scaling, swollen metal and rust that has pushed a pane out of place are a different level of problem.
2. Remove loose paint and rust with hand tools, such as scrapers and wire brushes, working back to bright, sound metal wherever possible. Loose paint is taken to a firm edge, and the edge is feathered so it doesn’t show through the finish.
3. Clean the metal of dust, grease and oils, and let it dry fully. Paint will not hold over residue.
4. Prime bare steel promptly. Bare steel can begin to flash-rust quickly, especially in a humid week, so the primer goes on the same day the metal is exposed, using a rust-inhibiting primer. The label should say it is suitable for steel or metal.
5. Finish with a coating made for metal, sometimes called direct-to-metal, in thin coats that don’t fill the profile of the bars.

Abrasive blasting is not the answer on historic steel or old glass. It can pit the metal and chip nearby glass, and it throws debris everywhere.

One safety point belongs here. Homes built before 1978 may contain lead-based paint, and steel windows from the 1920s–40s may well have it under later coats. The EPA’s Renovation, Repair and Painting program requires certified firms and lead-safe work practices for paid work that disturbs painted surfaces in pre-1978 homes, and the EPA’s RRP page explains the rule. Dry scraping and sanding old paint is the kind of work that makes dust, so know what is on the windows first. Our guide to lead paint in older homes covers testing.

What about the putty or glazing around the glass?

The glazing is the compound that bonds the glass to the frame and keeps water out of the joint. In older windows it is typically a putty-like glazing compound, and over decades it dries, shrinks, cracks and falls out. When that happens, water reaches the steel from behind and rust starts where you can’t see it.

Careful work checks every pane:

• Press gently along the glazing. Compound that is crumbly, missing or lifting from the glass needs replacing before painting, not painting over.
• Replace failed compound with a glazing product made for metal sash, and let it cure as the label directs before it’s painted. Cure times vary by product.
• Paint a hair onto the glass. The finish coat is carried a very small way onto the pane, so the paint seals the joint where compound meets glass. A coat that stops short leaves a gap that water finds. A coat that wanders far onto the glass looks sloppy, and it has to be scraped clean at the end.
• Check loose or rattling panes. A pane that moves is not held by anything, and the compound alone won’t keep it in.

Divided-light wood windows, with many small panes held by wood muntins, follow the same glazing logic. The difference is that the frame is wood, so it is scraped, sanded, spot-primed and painted as wood.

How do you keep windows from being painted shut?

This is the detail owners notice first, because a window that once opened easily, and now won’t, is a failed job no matter how good it looks. The cure is simple but careful:

• Hardware is masked or removed. Cranks, latches, handles and hinges are protected from paint, or taken off and cleaned so they can go back on.
• Coats are thin on the edges where sash meets frame. Thick buildup there is what glues a window shut.
• The sash is moved while the paint is still workable, opened and closed once or twice according to the paint’s directions, so a skin doesn’t bridge the gap.
• Weep or drainage openings stay clear. Some steel windows have small channels or holes that let condensation drain. Painting over them traps water. If you aren’t sure whether yours have them, ask before they are filled with paint or caulk.
• Check operation at the end. Every window is opened, closed and latched before the work is called done.

Michigan winters add condensation on cold steel, and the bottom rail often shows it first. A window that sweats every January and has peeling paint along the sill is telling you where to look.

How are leaded and divided-light windows cleaned and painted?

Leaded windows hold small pieces of glass in soft lead strips called came, with putty or cement packing the joint between glass and came. The metal is soft, and the glass is often old and fragile. Treat them gently:

• No forceful washing. Force can push water through the joints, loosen the glass and flex the came. Cleaning is by hand with a soft brush or cloth and mild soap and water.
• Don’t scrub or scrape the lead itself. Lead came usually isn’t painted. The paint job is the frame, sash and trim around the glass, with the leaded panel masked from drips.
• Don’t lean on the panel or press it flat. Many older leaded panels bow slightly over decades. Pushing them back can crack the glass.
• Look at the surrounding frame for rot or rust. The frame has to carry the weight of the panel, and a failing frame is the usual reason a panel sags.

If an exterior painting plan includes these windows, the point of care is what happens around them. Tudor Revival and French-inspired houses often pair them with stucco, stone or brick, and the paint line where the frame meets masonry has to be clean and sealed. Our guides to painting Tudor stucco and half-timbering and to painting French Eclectic and Norman homes look at those junctions.

When should a window specialist look at the windows?

Paint is a finish, not a repair. Some problems belong to a window restoration specialist or metalworker:

Rust that builds up in a joint can swell and push the frame apart, a problem usually called rust jacking, and it can crack the glass. If you see it, painting over it just hides the symptom.

If the house is historically designated, check with your city before changing exterior colors, materials or windows. Rules vary by community and by property.

What does this look like on a painting project?

Windows like these make a project slower, not harder, and they’re worth raising at the estimate stage so they are named in the written scope. Ask how rust, glazing, hardware and moving parts will be handled, and whether any window needs a specialist before painting begins. The exterior side should be painted in dry weather and within the label’s temperature range, which in Michigan means late spring through early fall for most work.

For the way Guiffre’s Painting Co. approaches older homes, see our exterior painting page. For the larger picture of the prep, conditions and checks behind a clean finish, read what a flawless paint finish takes.

Questions

Painting an older home in the Pointes?Plaster, original trim and old windows need a careful approach. Here’s ours.→