Windows – minor repairs

Summary: Learn how to make repairs to a window, replace a pane of broken glass, fit a new pane of glass, free a sticking casement window, repair a stiff sash mechanism, adjust a mortise fastener and repair a rotten window sill.

Stick masking tape over the pane to prevent the glass fragmenting.

Replacing a pane of broken glass

When removing a cracked windowpane, wear protective gloves and goggles.

  • Place a dustsheet under the window to catch any loose glass.
  • To prevent glass fragmenting, stick masking tape over each pane.
  • Tap the glass with a hammer to knock it out and careafully pull out pieces of glass from the frame by hand.
  • Use a putty knife or chisel to remove any putty and remaining glass.
  • Remove all pins and diamond-shaped glazing points with pincers or pliers.
  • Sand the frame lightly to ensure the surface is smooth.
  • Clean out the rebate frame and apply wood preserver and primer before inserting new glass.
Push the rolled putty into the rebate.
Trim the excess putty with a putty knife.

Fitting a new pane of glass

  • Take some putty and roll it in your hands until it has a smooth consistency which will make it easier to work with.
  • Roll the putty into strips of about 10mm (3/8in) in diameter and push the strips into the rebate.
  • Carefully position the new pane of glass into the rebate and press around the edges, so the putty holds it.
  • Using a pin hammer carefully tap glazing points or small pins into the timber frame around the pane of glass to keep it in place. The glazing sprigs or pins should not touch the pane of glass.
  • Push more strips of putty all around the pane of glass where it meets the rebate.
  • Trim away any excess putty with a putty knife. Then run the flat surface of the knife’s blade over the putty to a secure seal and smooth finish.
  • Clean any smears from the glass with white spirit.
  • Wait until the putty has dried before painting.

Freeing sticking casement windows

  • First try running a knife down the edges of the window to remove any paint or debris clogging the joint or tracks of the window.
  • Lubricate the edge of the window with candle wax.
  • If neither of these methods work, pull the window in to the frame as if closing it but without actually doing so and inspect the edge where it meets the frame. You should be able to see where the window is sticking.
  • Use a plane to shave off the area causing the window to stick.
  • If the window is sticking on the vertical edge you will be able to remedy the problem without removing the casement. But if the problem is on either the top or bottom edge it will have to be removed before planing.

Repairing stiff sash mechanisms

If a sash window is sticking, oil the mechanism and strip off any excess paint clogging the track. If this does not work, you may need to replace the cords, which is covered in replacing broken sash cords.

Use the cut out section as a template but cut your patch slightly bigger.
Plane the surface smooth.

Adjusting a mortise fastener

If the mortise fastener is not securely holding the window in the closed position it may be misaligned. You will need to remove the mortise-plate on the mullion and reposition it.

  • With a screwdriver remove the mortise-plate.
  • Position the plate so that the fastener connects with the mullion in the middle of the plate.
  • Draw around the central hole in the plate, and then around the outside of the plate.
  • Mark the position of screw holes and drill pilot holes.
  • Chisel out the central hole to a depth that will accommodate the mortise.
  • Screw the mortise plate to the mullion, and check the alignment.





Chisel out the central hole to a depth to accommodate the mortise.

Repairing a rotten sill

If a section of the sill is rotten or damaged, you can patch it rather than replacing the entire sill.

  • Use a hand saw to cut out the area of rotten wood as neatly as possible. Cut the ends to a mitre cut.
  • Use the section you cut out as a template for the patch but making it slightly bigger. Cut the patch with a mitred end to make a mitre joint with the existing sill.
  • Mark the position of the drip groove (drainage channel) under the sill.
  • Use a router to carve out a drip groove in the patch.
  • Apply primer to the cut edges.
  • Screw the patch in position with countersunk screws.
  • Plane the surface to a smooth finish and decorate.
  • If a large portion of the sill is rotten, then prise the sill away from the window and fashion a replacement, using the old section as a template. Widespread rot may require you to replace the entire window.

Tools needed

  • Claw hammer
  • Putty knife
  • Pincers OR pliers
  • Paintbrush
  • Pin hammer
  • Pen knife
  • Plane
  • Screwdriver
  • Power drill
  • Wood chisel
  • Panel saw
  • Router
  • Countersink drill bit

Materials needed

  • New pane of glass
  • Masking tape
  • Sandpaper
  • Wood preserver
  • Primer
  • Putty
  • Glazing sprigs OR pins
  • White spirit
  • Candle wax
  • Screws
  • Sandpaper

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