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Repairing a broken window - Part 1

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Always wear thick gloves and safety goggles when reglazing or repairing a damaged window containing broken glass.
A broken window is both a security risk and a safety hazard.


Replacement glass, new sprigs - angular metal nails (wooden frame), wire clips (metal frame), adhesive tape (optional), glass cutter (optional), hammer, pliers, pincers, putty(wooden frame -ordinary putty or metal frame - metal-casement putty), putty knife, primer (either wood-oil based primer or metal-aluminium based primer), thick gloves, goggles.

Temporary repair

If you need to secure the surface prior to replacing the glass, use a sheet of hardboard and secure with battens to the outer frame. It may be possible to tape polythene to the surface and cover the area. This will prevent rain entering the premises, but hardboard is more secure if it likely to be in position for a while.

If there is a crack rather than a break, use a clear adhesive waterproof tape along the cracks. This will give a temporary repair which should prove barely visible from the outside.

Removing the glass

Break out the broken window pane, using a hammer and pliers, and carefully catch and dispose of the glass, wrapping it in several layers of newspaper. It is sensible to use sticky tape in a star shape across the glass surface. This will stop the glass fragmenting too much when you tap it out. It may be necessary if there are some jagged pieces to grip each piece and remove separately. If the glass is cracked but not broken, use a clear adhesive waterproof tape along the cracks.

Use a glass cutter to score the surface around the edge of the glass. Tap out each broken section, using the adhesive tape as guides. If the job is not on the ground floor, try to have somebody helping and make sure the space below the window outside is completely clear. Levering out pieces around the edge will also break out putty.

Preparing the framework

If the putty is old and dry it will usually give way fairly easily. Sometimes the job is more time consuming as the old putty will need to be cut away with a woodworking chisel or a chopping knife, which is a straight-bladed knife with a thick back for hammering.

Preparation of a wooden frame

There will be sprigs (headless nails, which are small and wedge shaped) along the rebate which held the glass in a wooden frame. Pull them out with pincers. Before replacing glass, clean the rebates thoroughly and seal. Take care not to use too much force if you are replacing a pane in a multi-paned window, to avoid cracking an adjacent pane. Putty will soon become denatured and fall out if put on to bare wood. Use medium grade glasspaper to smooth the surface, before painting the rebate using an oil-based wood primer.

Preparation of a metal frame

In a metal frame there will be spring clips to remove. Make sure all old putty is cut out and the rebates are level and clean. The metal clips will be replaced once the glass is in position, therefore make sure the holes in the frame are clear. Paint the rebate, using an aluminium based paint on metal.

Measuring the replacement glass

Have the glass cut so that it is easy to fit. Measure the inside of the frame, including the rebate along the width and height. Take care and check the measurements, remember the glass should not have to be forced in, but must also sit comfortably inside the rebates. Allow approximately 3mm space all the way round if fitting into a wooden frame, due to wood naturally contracting and expanding. The width should be the first measurement stated when ordering. If you are using patterned glass, make sure you check the direction of the pattern run before it is cut. Buy the glass of the same thickness as that removed, but if this is not known most windows can be 3mm or 4mm. Larger windows should use 6mm thickness. As a general rule:

3mm is suitable for windows with a surface area equivalent to 1 square metre (10.75 square feet). 4mm is suitable for windows with a surface area equivalent to 2.6 square metres (28 square feet).

6mm is suitable for windows with larger surface areas.

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