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How to fix and fit window frames


1st Jan 2015 Home & Garden

How to fix and fit window frames

Well fitted window frames prevent drafts and can allow you to cut your heating costs. Follow our simple steps for a warmer home.

Gaps around the outside of frames will result in damp appearing on the internal walls around the window. It'll also encourage rot to attack the frames. Cracks up to about 10mm wide can be filled with frame sealant.

What you'll need:

  • Trimming knife
  • Thin screwdriver
  • Clean rag
  • Frame sealant and applicator
  • A jar of water

1. With a trimming knife, cut the nozzle off the sealant cartridge at an angle to give the necessary width of sealant to fill the gap. Break the foil seal or cut the sealed top of the cartridge.

applying sealant

2. Wipe around the frame with a clean rag, and inject a bead of sealant into the crack all round. The sealant should be placed in the angle between the window frame and the wall. For neatness, try to inject the sealant in a single run without stopping, except at corners. Release the trigger to stop the flow.

3. If it's necessary to smooth the sealant, use a wet finger.

4. Sealant can be painted once a skin has formed (1 to 3 weeks), but it isn't necessary.


Sealing with mortar

If the gap is more than about 10mm wide it should be filled with mortar, which is available in small bags—ideal for jobs of this scale.


What you'll need:

  • Plant sprayer 
  • Small trowel or filling knife
  • Trimming knife
  • Clean rag
  • Water 
  • Mortar
  • Sealant and applicator

dampen the crack

1. Dampen the crack with water. A plant sprayer is ideal.

applying the mortar

2. Press the mortar in place with a small trowel or filling knife, so that it is level with the surface of the brickwork.

3. When the mortar has hardened, which will take 2 or 3 days, seal all round the frame with frame sealant as described above.


For large, irregular gaps that are hard to reach, use a can of expanding foam filler. This adheres to most building materials. It is injected by nozzle at any angle, after which it expands in volume, effectively sealing even hidden areas. Once hardened, the foam is heat, cold and water resistant and rot-proof. It can be cut, sanded, plastered or painted.

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