How do I reglaze a window with linseed oil putty?

Remove all old loose glazing. Clean the rabbet (the groove the glass sits in). Apply a thin bed of glazing compound in the rabbet. Set the glass and secure with glazier's points every 6 to 8 inches. Apply facing compound with a putty knife, tooling to the standard triangular profile. Prime within two weeks. Paint with two finish coats.

What is the correct angle for the glazing bead on a window?

The triangular bead runs from the face of the sash wood at approximately a 45-degree angle to the glass surface, with the thin edge touching the glass and the wider base against the sash. The bead should not extend above the sight line of the sash (the inner edge of the rabbet visible from inside) or onto the glass face.

Why does my window glazing keep cracking and falling out?

Almost always because the wood under the glazing is bare and unprimed. Bare wood absorbs the oil from the glazing compound before it cures, leaving the compound oil-depleted and brittle. Prime the bare wood rabbet with oil-based primer before applying new glazing compound.

Historic Putty Glazing Compound — Old Canaan Building Materials

Linseed oil glazing compound has been used to bed glass in wood sash since windows have had glass in them. It has not been improved upon for this specific application in three hundred years. The alternatives — latex glazing compound, silicone, and various caulks — are inferior in every measurable way for the purpose of bedding and facing glass in a wood sash. This is one of those cases where the original material is the correct material, and the alternatives exist because they are cheaper, not because they are better.

The Character

Traditional glazing compound, correctly applied, forms a smooth triangular profile from the wood sash to the glass face — wider at the sash, tapering to a fine edge at the glass. Painted, it is invisible. Fresh compound is plastic and oil-rich. Over weeks it skins over. Over months it cures to a firm, slightly flexible mass. Over years it becomes hard and eventually brittle — which is when it needs renewal.

What It Is

Linseed oil glazing compound is white lead or calcium carbonate pigment suspended in boiled linseed oil, with driers added to accelerate curing. The standard product is Sarco Type M, still manufactured and available through glass suppliers. It is available in cans and in rope form for bedding glass before setting. Dap 33 is the most widely available but is an inferior product — it dries harder and more brittley than Sarco and does not last as long.

How It Behaves

Linseed oil glazing compound skins over in a few days and should be primed and painted within two weeks. Unpainted compound does not cure properly — the linseed oil needs to be sealed by paint to complete curing. Correctly primed and painted compound lasts 15 to 20 years before renewal is needed.

Why It's Right

Linseed oil glazing compound bonds to both wood and glass. It remains slightly flexible as it cures, accommodating the seasonal movement of the wood sash. It accepts paint. It is the material the sash was designed to receive. Latex glazing compounds do not bond to glass as reliably and do not last as long. Silicone does not accept paint.

How To Get It

Sarco Type M from glass suppliers and specialty building materials dealers. Do not substitute Dap 33 for significant reglazing work — the quality difference is meaningful over the 15-year service cycle.

The Old Canaan Standard

Sarco Type M linseed oil glazing compound, triangular profile from sash to glass, primed within two weeks of application, for all wood window sash reglazing on traditional New England buildings. Prime with oil-based alkyd primer. Two oil-based finish coats. This is the only correct material for this application.

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Historic Putty Glazing Compound

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