How to seal gaps for a more energy efficient home

Gaps around door and window frames, holes where pipes go through walls and warped or poorly fitted skirting boards let heat escape and moisture creep in. Seal them with these simple techniques.

How to seal gaps for a more energy efficient home

Getting started

Choose the right sealant for the job. For gaps between different materials (brick and wood, for example), you need a flexible acrylic or silicone-based sealant that will allow for any slight movement in future. Flexible sealants come in cylindrical cartridges that fit into a trigger-operated cartridge gun for use. For larger gaps, use expanding foam filler or decorating filler, built up in stages.

Before you start

Make sure that the area you're going to work on is clean and sound, otherwise the sealant won't stick.

  • Clean off dirt and dust with a cloth and check that any paintwork is in good condition.
  • Rub it down and repaint it, if necessary, before tackling the sealing.
  • Scrape out any old sealant with a putty knife, screwdriver or a razor blade, taking care to remove it all.

Applying sealant

  1. Snip off the end of the nozzle at a 45 degree angle so that the hole at the tip is about half as wide as the crack you have to fill. Don't make it too wide.
  2. Squeeze the trigger of the cartridge gun to start the flow of sealant.
  3. Start at one end of the gap and, with a steady hand, move slowly and evenly along the gap. You'll need to release and squeeze the trigger again from time to time.
  4. Use your thumb to release the locking bar on the piston to stop the sealant flowing when you have finished or need to stop.
  5. Use a wet finger or a sealant-shaping tool to make sure that the sealant has a neat finish and is well bedded into the crack.

Sealing deeper gaps with expanding foam filler

For deep, wide or awkward-shaped gaps, expanding foam is the easiest solution for a neat finish.

  1. Always wear protective gloves, as the filler is very sticky when wet.
  2. Practise with the can before you start the job. The foam comes out surprisingly fast and expands to up to 60 times its original volume. Some fillers expand less than others; check the label.
  3. Spray the gap with a little water to dampen it before filling.
  4. Squirt a bead of foam into the gap and allow it to expand.
  5. Leave it to dry for up to two hours, then cut away the excess with a hacksaw or sharp knife. Wear a face mask to protect you from the dust.
  6. Sand the surface smooth if you want to paint over the repair.
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