Starting with Condition Assessment
Before any material is removed, the full condition of a window should be recorded. A methodical inspection determines which components can be retained with minor repair and which require more involved treatment. Working without a clear assessment leads to over-stripping or missing areas of incipient decay.
The four areas to examine are: the sill (bottom horizontal member, most exposed to moisture), the head (top horizontal member, often concealed under casing), the stiles (vertical members running the full height), and the glazing bars if present. Each should be tested with a pointed tool pressed lightly into the grain — sound timber resists, softened or punky wood gives way.
Paint condition is assessed separately. Alligatoring, deep cracking, and lifting indicate moisture is present below the surface. A flat surface with fine crazing simply indicates age and surface oxidation.
Paint Removal
The goal is to remove paint that is failing or obscuring the frame geometry, not to strip every coat as a matter of habit. Excessive stripping of sound layers removes the oil content that has migrated into the timber surface over decades.
For softwood frames with multiple thick paint coats, an infrared heat tool set to a moderate temperature is preferable to an open flame or chemical stripping, both of which carry their own risks — fire or grain-raising respectively. The infrared tool softens the paint without scorching the timber, and a shavehook or scraper removes the lifted material cleanly.
Around Glass
Stripping close to glazing requires a hot-air tool with a deflector nozzle, keeping heat well away from the putty line and the glass edge. Sudden temperature change across the glass surface risks cracking. Working in short passes and keeping movement constant reduces this risk.
Where original putty is still sound — adhering to both glass and rebate, without cracks that track across the full width — it does not need to be replaced. Intact putty can be painted over directly after a light sanding.
Consolidating Localised Rot
Localised soft areas, typically at sill ends, at mortice joints, and at the base of stiles, can be treated in place rather than replaced, provided the structural integrity of the joint is not compromised. The two-stage approach uses a penetrating epoxy consolidant followed by a two-part epoxy filler.
The affected area must be dry before treatment begins — moisture content below 18% is the standard threshold. This may require leaving the window open or using a dehumidifier in a damp room for several days before proceeding.
The consolidant is brushed generously into the softened timber and allowed to cure for the time specified by the manufacturer, typically 24 to 48 hours at normal temperatures. The filler is then mixed according to instructions and applied in layers, shaped with a scraper or moulding tool to match the original profile, and sanded after curing.
Draught-Proofing
The gap between sash and frame that allows air infiltration is the primary thermal weakness of single-glazed historic windows. Fitting a blade-type or pile weather-stripping around the sash perimeter reduces draughts without altering the visual character of the window and without permanent modification to the timber.
Blade seal strips are recessed into a routed channel in the frame rebate. Pile strips are surface-mounted with adhesive or staples. Both are available in neutral grey or brown tones and are largely invisible when the window is closed.
Re-Glazing with Linseed Oil Putty
Where putty has failed — cracked, shrunk, or detached — glass should be re-bedded. The procedure is the same for face putty (the visible triangular bead on the outside) and back putty (the thin seating layer behind the glass in the rebate).
The rebate is cleaned back to bare wood, dusted, and primed with raw linseed oil. A thin back putty bed is pressed into the rebate. The glass is pressed into the bed and secured with glazing sprigs (small cut nails tapped flush). Face putty is then pressed along the front and struck to a 45-degree angle with a putty knife. Linseed oil putty requires a minimum of two weeks to skin over before painting.
Detailed guidance on putty preparation and working methods is covered in the article on traditional putty glazing techniques.
Priming and Painting
Bare wood must be primed before any topcoat is applied. An oil-based primer — either traditional lead-free alkyd primer or a micro-porous water-based equivalent — seals the timber and provides the key for subsequent coats. Two topcoats of an oil-modified paint formulated for exterior joinery give the best durability.
Paint should not be applied to wet timber or in temperatures below 8°C. Painting over putty that has not fully skinned over traps oil and prevents normal curing.