Replace a cracked pane in a single-glazed timber window — HomeGraft

Remove broken glass safely, fit a new pane with putty and sprigs, then paint once it's skinned over.

RP-01Protect the area and gather toolsLay a dust sheet under the window inside and out to catch glass slivers and putty scraps. Put on thick gloves and safety glasses - broken glass edges are sharp and easy to miss. Clear furniture and open nearby doors so you have room to work without reaching over the glass.

1 each · Dust sheet

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1 pair · Heavy-duty work gloves

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1 pair · Safety glasses

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1 each · Cardboard box for glass waste

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RP-02Check whether the pane needs safety glassIf the window is less than 800mm above floor level, in a door, or within 300mm of a door edge, Building Regulations require toughened or laminated safety glass rather than ordinary glass. Tell your glass supplier the exact location and height so they cut the correct type. This applies to a replacement pane, not just new installations.

RULES

KNOW THE RULES

Approved Document K covers safety glazing in critical locations - low windows, doors, and glazing next to doors. Using ordinary glass in these spots is a genuine safety and compliance issue.

RP-03Remove the broken glassWearing gloves, wiggle loose shards free by hand and place them straight into a box or onto an old towel. Tap larger stuck pieces gently with a hammer handle if they won't come away. Wrap every piece before it goes in the bin - loose glass in a bin bag can cut whoever empties it.

RP-04Strip out the old putty and sprigsChop out the hardened putty from the rebate with a hacking knife and mallet, or a stiff scraper. If it's rock hard, soften it first with a heat gun on a low setting, keeping it moving so you don't scorch the timber. Pull out any old glazing sprigs (small nails) with pincers as you go.

1 each · Hacking knife

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1 each · Pincers

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RP-05Clean and prime the rebateSand the bare wood rebate lightly to remove flakes, splinters and old paint. Brush out all dust, then apply a coat of wood primer and let it dry fully. Bare wood draws the oil out of fresh putty and makes it crack early, so don't skip this.

250 ml · Wood primer

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1 sheet · Sandpaper, medium grit

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RP-06Measure and order the new glassMeasure the rebate width and height at two points each way, then subtract 2mm from each dimension for clearance. Check the thickness of the old glass - most single-glazed panes are 3mm or 4mm - or ask your supplier to match it. Order from a local glazier; large sheets are awkward and risky to cut yourself.

1 each · Replacement glass pane, cut to size

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RP-07Bed the new paneRoll a thin, even bead of glazing putty into the clean rebate with your fingers. Press the new pane into the putty from the outside, pushing gently at the edges only - never the middle - until it sits flat with an even squeeze-out of putty all round.

1 kg · Linseed oil glazing putty

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RP-08Fix the pane with glazing sprigsTap small glazing sprigs into the wooden rebate every 150-200mm to hold the glass in place. Slide each sprig in flat against the glass using the flat of a hacking knife rather than hammering directly on the pane. This holds everything steady while the outer putty sets.

20 each · Glazing sprigs

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RP-09Apply and shape the front puttyPress a roll of putty into the angle between the glass and the rebate all the way round. Draw a putty knife along at a steady 45° angle to leave a smooth triangular fillet, mitring the corners neatly. Trim off any excess putty left on the glass with the knife.

1 each · Putty knife

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RP-10Clean up and let the putty skin overScrape any putty smears off the glass while it's still soft, then wash your tools and hands with white spirit. Leave the putty to skin over for about two weeks before painting - a gentle poke will tell you when it's firm enough. Keep the window closed and undisturbed during this time.

500 ml · White spirit

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RP-11Paint the putty to finishOnce the putty has skinned over, paint it with an exterior-grade paint matching the rest of the frame. Overlap the paint onto the glass by about 2mm on all sides - this overlap is what actually keeps water out of the joint, so don't leave it bare.

250 ml · Exterior gloss or satin paint

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1 each · Small paintbrush

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