Douglas Kent, Technical and Research Director, shares his practical advice on maintenance and care of windows
Frequent and straightforward
Many owners assume that old windows showing signs of wear or decay are near the end of their life, but deterioration is often only superficial. With regular maintenance, historic timber and metal windows can remain sound and functional for centuries — far outlasting a lot of modern replacements.
All windows experience gradual wear, so regular inspection and upkeep are essential to their longevity and smooth operation. They should be examined carefully at least once a year, with any necessary work planned and carried out as appropriate. Check them additionally after severe weather or prolonged damp conditions.
Too frequently, old windows are discarded unnecessarily because of minor faults that could be easily remedied through simple maintenance. While some tasks are best left to skilled contractors, much routine care can be undertaken by DIYers using basic tools and materials.
Window frames
Sticking windows are harder to operate and may lead to cracked glass. Where binding results from paint build-up or wrongly decorated parts, use a chemical stripper. Sliding sashes that stick may need a general overhaul, including, for example, adjusting tight beads or replacing cords. Distorted frames can be lightly planed or sanded, though major distortion may indicate structural problems like a failed lintel or wall movement. Avoid easing windows in damp or unheated buildings, as sashes often free themselves when conditions change.
Small areas of timber decay or surface defects can be built up with a two-part filler or linseed putty but first resolve any leaks or sources of dampness. Proprietary metal fillers can patch holes or defects in metal frames.
Cracked or missing mortar (‘pointing’) between the frame and wall may admit moisture and draughts. Repairs should match existing material unless past work was unsuitable. Haired lime mortar or burnt sand mastic — a mix of baked sand and boiled linseed oil — can seal the frame-to-wall joint, with the void behind packed with dampened newspaper.
Reapply defective weatherstripping as needed. On sliding sashes, replacement beads with seals usually cure draughts and rattles. Alternatively, as a temporary solution, use small timber or rubber wedges. Excessive wear that allows sashes to move too freely may necessitate their re-edging or the filling of worn grooves. Maintain secondary glazing by tightening fittings, checking seals and lubricating moving parts.
Glass
Minor cracks in old putty can be sealed with putty thinned using a few drops of raw linseed oil or natural turpentine, extending its life for several years. Replace any failed putty. Hard or brittle areas may be softened by prolonged contact with raw linseed oil, a citrus- or solvent-based remover, or, on timber frames, gentle warming with an infrared putty lamp.
When re-puttying, form a smooth fillet with a putty knife and cut a clean line along the sightline where it tapers onto the glass. With metal windows, use a metal window glazing compound or butyl-based mastic instead of linseed putty.
Leaded lights (small-paned windows with lead strips) may leak as the glazier’s cement — a linseed oil and whiting mix — deteriorates. It can sometimes be revived in situ by brushing on several coats of a 50:50 mixture of boiled linseed oil and turpentine.
Certain glazing, such as stained glass, requires specialist care. Most other windows benefit from cleaning every few months: remove dust with a duster or soft brush, then wipe with a microfibre cloth dampened with plain water. Periodic dusting between cleans helps keep surfaces fresh. For more thorough cleaning, use deionised water or a neutral soap solution. Microfibre cloths can also remove condensation to protect frames and prevent mould.
Very fine scratches on old glass may sometimes be reduced with jeweller’s rouge (a polishing compound made from finely ground iron oxide that gives a high shine to precious metals), but marks that are deeper or on historically important glazing need specialist attention because of the risk of damage.
Ironmongery
Hinges, pulleys, fasteners, weights, stays and similar fittings are often overlooked, yet are essential to proper window operation. Check that all screws and fixings are secure and correctly aligned, ensuring moving parts work freely. Ironmongery should only be removed if it is loose or at risk of loss or damage. Worn hinges can frequently be repaired by replacing pins or inserting small steel washers between the knuckles. If fittings are missing or beyond repair, source new ones that match the originals in size and design.
Clean visible ironmongery annually using a microfibre cloth or soft natural-bristle brush. With brass and bronze, avoid scouring pads and metal polishes because they can cause damage. If dirt persists, use warm water with a little neutral soap, then dry thoroughly.
Once clean and dry, lightly lubricate moving parts with a proprietary light penetrating oil rather than grease, which attracts dust and hardens over time.
There may sometimes be a case for using bespoke ironmongery to adapt lower sliding sashes in windows to open inwards for easier cleaning and maintenance.
Paint and finishes
Maintain the decorative finish on windows, especially those of painted softwood. Localised touching-up is often sufficient; complete paint removal is rarely necessary or desirable, even when fully repainting. Follow Health and Safety Executive guidance where old lead paint may be present. Protect glass carefully with masking tape and stiff cardboard to avoid damage, such as scratches from abrasive sanding paper.
Remove only loose or defective paint, putty or filler with a scraper. Surface rust on metal components can be cleaned mechanically using small scrapers, brass wire brushes or fine wire wool. Essential paint removal — for instance, where build-up clogs anti-capillary grooves, drips or decorative mouldings — may be undertaken with a chemical paint remover.
Lightly key painted timber surfaces with wet-and-dry abrasive paper before painting and between coats for a smooth finish. Fill cracks or irregularities before repainting. Apply a compatible new paint system: alkyd paints are commonly used, while linseed oil paints, with a linseed oil–based anti-rust primer on metal parts, offer a durable alternative.
Carry the paint slightly over the junction between glass and putty (about 1 mm) to form an effective moisture seal. Proprietary edge tape or paint shields can help achieve a neat line.
Some components must remain unpainted to ensure smooth operation — for example, the junction between a pulley stile and sash stile, which can instead receive a thin coat of beeswax mixed with linseed oil or tallow. Such blends also help keep cords supple and rot-resistant.
Download Repair of Wood Windows Technical Advice Note
Watch SPAB's How to... repair, re-cord and re-glaze timber sash window videos
Images: © SPAB