The yard / Reuse guides / G-02
Reuse guide 02 - bin B-07 stock
Re-glazing a wood sash in an afternoon
The sash that came out of a church side wall is straight-grained old wood with good glass in most of its lites. What failed was the putty, not the sash and not the glass. That is the common case in this yard, and it is the easiest thing in the world to fix badly: pry at the glass, skip the oil, and bead the compound on cold. Do it in the right order and an afternoon is enough for one sash.
Old glass does not care how careful you were yesterday. It cares about today.
Before you start, decide what the sash is for. A garden sash or a shed pane is a forgiving job. Glass above a door, over a walkway or in a school is not a bench project - talk to a glazier about that opening. The yard gives no guarantee on glass, and you should not take one from anybody else.
The re-glaze, in order
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Take the sash out and lay it flat
Two sawhorses, sash horizontal, glass side up. Note which way it hung and which edge met the parting bead, and write it on the rail in chalk. Sash are handed by a hundred years of weather, and they go back one way only.
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Cut-resistant gloves on, then the old putty out
Warm the failed bead briefly with a heat gun on low - it softens in seconds - and lift it with a stiff scraper working from the outside in. Never lever against the glass. Most of the old putty will come away in long strips; the rest scrapes off with the rebate exposed.
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Judge each pane before you lift it
Flat, clear, edges unchipped, no hairline at the corner: keep it, and keep it in order. Any crack, any deep edge chip, any pane that has been flexing in a loose rebate: out. Salvaged glass is racked in B-07 by size, so a replacement is usually on the shelf.
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Clean the rebate to bare wood
Scrape, brush, and vacuum. Old compound leaves an oily film and dust that will keep the new bead from gripping. While the rebate is bare, look hard at the corners and the bottom rail - that is where water sat and where rot starts.
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Deal with any rot now, not later
Soft wood in a corner gets cut out and Dutchmaned with the same species. Glazing onto rotten wood buys you one winter. If more than a third of the bottom rail is soft, the sash is a donor, and the yard will say so.
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Oil or prime the bare rebate
A thin coat of boiled linseed oil or a glazing primer on the bare wood, wiped back so it is not glossy. Dry wood drinks the oil out of glazing compound and the bead cracks in a year. This step takes four minutes and is the one everybody skips.
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Bed the pane on a ribbon of compound
Knead the compound until it is soft, roll a thin ribbon, press it into the rebate, then set the glass and work from the centre out with your thumbs - flat pressure, never an edge, never a corner. Squeeze until a little compound shows around the whole pane.
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Set the glazing points
Two per edge on a small lite, pushed in flat against the glass with the corner of a putty knife and driven home. They hold the pane while the compound cures; they are not the weather seal. Points set too deep crack the glass from the edge inward, sometimes months later.
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Back-putty, then bead the face in one pass
If you can reach the inside, skim a thin back bead first and let it firm up. Then the outside face: a knife at about 45 degrees, drawn along in one continuous pass, corners cut with the point. Dip the knife in water or oil so it does not drag. One clean pass beats three ragged ones.
Then leave it alone
Glazing compound skins in a few days and cures over weeks. Do not paint before it has skinned, do not close the sash tight while the bead is soft, and do not press a fingerprint in to check. The sash can go back in its opening once the bead is firm; the paint waits.
Count three to four hours for a six-lite sash, and a full day if a corner needs a Dutchman. Keep the old glass you take out: a cracked pane is still a template, and a flat clear one may go into the next sash through the yard.