Strip old putty from a timber window, refit the glass, reputty neatly, then leave to skin before painting.
RG-01Prepare and check the weatherPick a dry day above 5°C — putty won't bed or skin properly in cold or damp conditions. Lay dust sheets below the window and wear gloves and safety glasses, since old glass and putty flakes can be sharp. If it's a removable sash, take it out and work flat on a bench rather than in the frame.
RG-02Strip out the old puttyChip away the old, brittle putty on the outside face using a hacking knife and mallet, or an old chisel. Work along the grain of the putty line and angle the blade away from the glass so you don't crack it. Get right down to bare wood in the rebate.
RG-03Remove the sprigs and lift out the glassOnce the putty is clear, pull out the small glazing sprigs (nails) with pliers. Support the pane with one hand as you remove the last few — it can drop free suddenly. Lift the glass out and rest it on a folded blanket, not bare on the floor.
1 each · Old blanket or thick cloth RG-04Check the glass and replace if neededLook the pane over for cracks or chips. If it's damaged, measure the rebate opening and take it to a glazier — they'll cut a new pane about 2-3mm smaller than the opening all round so it seats without binding. If the glass is sound, just clean both sides ready to refit.
1 each · Glass cleaner and cloth RG-05Clean and prime the rebateWire-brush the bare wood rebate to clear every trace of old putty and dust, then give it a light sand. Paint on a thin coat of wood primer or linseed oil and let it dry fully before continuing. This stops the bare wood pulling oil out of the new putty, which makes it crack early.
1 small tin · Wood primer or linseed oil 1 each · Small paintbrush RG-06Bed a thin layer of puttyKnead a ball of glazing putty in your hands until it's soft and pliable, with no cracks. Press a thin bed, about 2-3mm deep, into the rebate with your thumb all the way round. This cushions the glass and keeps damp from getting in behind it.
1 500g tin · Linseed oil glazing putty RG-07Set the glass and pin it with sprigsPress the pane into the bedding putty, pushing at the edges (never the centre) until it sits flush. Tap in new glazing sprigs every 200-250mm around the frame, laying them flat against the glass so nothing sticks up.
RG-08Apply and shape the front puttyRoll a sausage of putty and press it into the rebate over the sprigs. Run a putty knife along at a steady angle to form a neat, even bevel from the sight line down to the edge of the rebate, mitring the corners as you go.
1 each · Putty knife (glazing knife) RG-09Trim and clean up the glassTrim any excess putty at the corners while it's still soft, and scrape smears off the glass with a blade or fingernail. Wipe the pane clean with a dry cloth so no putty film is left to dry hard on the glass.
RG-10Leave the putty to skinLet the putty skin over for at least 5-7 days before painting — longer if the weather's cold or damp. Painting too soon traps moisture underneath and the putty will crack within a season. Leave the window shut but don't force it, so the new putty isn't knocked while soft.
RG-11Paint the puttyOnce it's skinned over, paint the putty with undercoat then a exterior gloss or satinwood, carrying the paint about 2mm onto the glass. This seal is what actually keeps the putty weatherproof — unpainted putty fails within a year or two.
1 small tin · Exterior undercoat 1 small tin · Exterior gloss or satinwood paint RG-12Tidy up and dispose of wasteSweep up putty scraps and old sprigs. Wrap any broken or offcut glass in cardboard or newspaper, tape it up and label it clearly before binning it. If you used oil-based putty, clean tools with white spirit rather than water.
1 small bottle · White spirit 1 each · Cardboard or newspaper for glass disposal Some links may earn us a small commission at no extra cost to you.
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