A preliminary step in the routine maintenance of steel windows
is to remove surface dirt and grease in order to ascertain the
degree of deterioration, if any. Such minor cleaning can be accomplished
using a brush or vacuum followed by wiping with a cloth dampened
with mineral spirits or denatured alcohol.
If it is determined that the windows are in basically sound condition,
the following steps can be taken:
- removal of light rust, flaking and excessive paint;
- priming of exposed metal with a rustinhibiting primer;
- replacement of cracked or broken glass and glazing compound;
- replacement of missing screws or fasteners;
- cleaning and lubrication of hinges;
- repainting of all steel sections with two coats of finish
paint compatible with the primer; and
- caulking the masonry surrounds with a high quality elastomeric
Recommended methods for removing light rust include manual and
mechanical abrasion or the application of chemicals. Burning off
rust with an oxyacetylene or propane torch, or an inert gas welding
gun, should never be attempted because the heat can distort the
metal. In addition, such intense heat (often as high as 3800 deg.
F) vaporizes the lead in old paint, resulting in highly toxic
fumes. Furthermore, such heat will likely result in broken glass.
Rust can best be removed using a wire brush, an aluminum oxide
sandpaper, or a variety of power tools adapted for abrasive cleaning
such as an electric drill with a wire brush or a rotary whip attachment.
Adjacent sills and window jambs may need protective shielding.
Rust can also be removed from ferrous metals by using a number
of commercially prepared anticorrosive acid compounds. Effective
on light and medium corrosion, these compounds can be purchased
either as liquids or gels. Several bases are available, including
phosphoric acid, ammonium citrate, oxalic acid and hydrochloric
acid. Hydrochloric acid is generally not recommended; it can leave
chloride deposits, which cause future corrosion. Phosphoric acidbased
compounds do not leave such deposits, and are therefore safer
for steel windows. However, any chemical residue should be wiped
off with damp cloths, then dried immediately. Industrial blow-dryers
work well for thorough drying. The use of running water to remove
chemical residue is never recommended because the water may spread
the chemicals to adjacent surfaces, and drying of these surfaces
may be more difficult. Acid cleaning compounds will stain masonry;
therefore plastic sheets should be taped to the edge of the metal
sections to protect the masonry surrounds. The same measure should
be followed to protect the glazing from etching because of acid
Measures that remove rust will ordinarily remove flaking paint
as well. Remaining loose or flaking paint can be removed with
a chemical paint remover or with a pneumatic needle scaler or
gun, which comes with a series of chisel blades and has proven
effective in removing flaking paint from metal windows. Wellbonded
paint may serve to protect the metal further from corrosion, and
need not be removed unless paint buildup prevents the window from
closing tightly. The edges should be feathered by sanding to give
a good surface for repainting.
Next, any bare metal should be wiped with a cleaning solvent
such as denatured alcohol, and dried immediately in preparation
for the application of an anticorrosive primer. Since corrosion
can recur very soon after metal has been exposed to the air, the
metal should be primed immediately after cleaning. Spot priming
may be required periodically as other repairs are undertaken.
Anticorrosive primers generally consist of oilalkyd based paints
rich in zinc or zinc chromate. (2) Red lead is
no longer available because of its toxicity. All metal primers,
however, are toxic to some degree and should be handled carefully.
Two coats of primer are recommended. Manufacturer's recommendations
should be followed concerning application of primers.
(2) Refer to Table IV. Types of Paint Used for Painting Metal
in Metals in America's Historic Buildings, p. 139. (See bibliography).