How to Protect Window Sills

Written by dannah swift
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If you find that you're constantly repainting a particularly vulnerable wood windowsill, you might consider protecting it with a metal overlay secured to the sill. Aluminium is an excellent choice for such a project because you can purchase it in sheets and cut it to shape with tin snips. Paint the aluminium the same colour as the surrounding window frame to disguise it.

Skill level:

Things you need

  • Sheet aluminium
  • Double-sided tape
  • Utility knife
  • Tin snips
  • Caulk
  • 1-inch roofing nails
  • Hammer
  • Scrap wood (1 inch thick and as long as the windowsill)
  • Metal primer
  • Paintbrush
  • Exterior paint

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  1. 1

    Make a paper template of the sill. Fit a piece of paper onto the sill and into the edges and crevices of the sill, and draw an outline of the area to be covered.

  2. 2

    Cut out the template and lay it on a piece of sheet aluminium.

  3. 3

    Secure the template to the metal with double-sided tape. Place the tape along the edges of the template and press the paper onto the metal. Smooth out any wrinkles.

  4. 4

    Mark the outline of the pattern with a utility knife. Cut out the pattern with tin snips.

  5. 5

    Lay a bead of caulk around the edge of the sill stool. The stool is the top part of the sill that faces the sky. Fit the aluminium cutout to the sill and press it into the caulk. Hammer 1-inch roofing nails every 2 inches along the edges of the metal.

  6. 6

    Secure a piece of scrap wood -- about an inch thick and the length of the sill -- to the section of the aluminium that fits over the edge of the sill. Hammer along the piece of wood to force the metal to conform to the shape of the sill. Once the edge has formed, remove the wood and secure that edge to the sill with 1-inch nails placed every 2 inches.

  7. 7

    Caulk around the edge of the aluminium where it meets the wood of the window frame to prevent moisture from being trapped underneath the metal. Do not caulk along the window itself.

  8. 8

    Prime the aluminium with metal primer. Paint on the primer and let it dry, then paint the aluminium with a high-quality exterior paint to match the window frame.

Tips and warnings

  • Keep in mind that this is a quick fix for a problem that really should be addressed by replacing the windowsill. If a windowsill consistently suffers from some sort of damage, there may be other problems at play that should be looked into.

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