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How to make a window sill

Getting someone else to do a job for you can be costly. But with the right approach you can do a lot by yourself. You’ll save time and money by using the handy step-by-step instructions that you’ll find on the SKIL website. These step-by-step instructions are divided into categories relating to the different kinds of jobs in and around the home, and give you clear, A to Z explanations.

Just click on one of our step-by-step instructions and you’ll be able to get started right away!

  1. Fit a new window sill on top of the old one

    If you can’t or don’t want to remove the old window sill, you can always use a new window sill that simply fits on top of the old one. These often have a scratch-resistant surface, and are secured using construction adhesive.

  2. Remove the old window sill

    If you want to remove the old window sill, you first need to cut away the sealant edges with a utility knife. Once you’ve loosened the sealant edges, try to pull the window sill away. If it’s difficult to do this, try to lift the window sill off from underneath.

  3. Remove sealant and adhesive residues

    When you’ve taken the window sill off, you can remove the remaining sealant and adhesive with a filling knife. If the wall has been damages by removing the window sill, you can repair it with filler or plaster.

  4. Horizontal check

    Before you fit the new window sill, you need to check that the underlying surface is flat and horizontal. Use a spirit level and make the surface perfectly flat and horizontal. That will ensure good adhesion of the new window sill.

  5. Measure the width of the window frame

    Measure the width of the window frame or wall, and measure how deep (A+B) you want to make the window sill. If you want the window sill to extend along the wall (C1+C2), measure the angle accurately with a try square. Then, it’s best to make a template out of sturdy cardboard. Use this to mark out the angles on the window sill. In practice, the straight line of the window sill doesn’t always exactly match that of the wall.

  6. Mark out the window sill

    Mark out the required shape and dimensions of the new window sill. Use a try square to mark out a right-angled line. Carefully position the cardboard template, and transfer the angle onto the window sill with a pencil.

  7. Saw the window sill to size

    Use a jigsaw with a fine-toothed blade. To prevent splintering of the top layer, put a strip of transparent tape over the sawing line that you’ve marked out. Then saw the window sill to size and apply tape neatly over the outside edges and the veneer surface strip. If the veneer strip has an adhesive layer, fix it in place with a clothes iron. When the adhesive is dry, trim the veneer strip neatly to size with a sharp knife. Then sand the edge smooth with fine sandpaper.

  8. Fit the window sill

    When the window sill fits perfectly between the walls, apply construction adhesive to the underlying surface. Use a sealant gun to apply equally sized and spaced spots of adhesive. Then, lay the window sill on the surface and press it firmly in place. Check that the window sill is horizontal using the spirit level. Wait for the adhesive to dry, and then fill any gaps and joints with white acrylic sealant.

  9. Fit a finishing strip

    You might find that the window is damaged on the underside of the window frame, or you might want to create a classic look. If so, you can fit a suitable finishing strip. Saw this to size and fix it in place with construction adhesive.


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