Introduction
A well-fitted window board (also called a window sill or window ledge) finishes off a window reveal cleanly and adds a practical surface for plants, ornaments, or simply a neat finish. MDF moisture-resistant window boards are the go-to choice for UK homes — stable, paintable, and built to last.
What You'll Need
- MDF moisture-resistant window board
- Mitre saw or jigsaw
- Adhesive (grab adhesive or No More Nails)
- Spirit level
- Caulk and decorator's filler
- Sandpaper
- Tape measure and pencil
Step 1 — Remove the Old Window Board
If replacing an existing board, use a bolster chisel to carefully lever it away from the wall. Clean up any old adhesive or plaster.
Step 2 — Measure the Recess
Measure the width of the window recess and the depth from the wall face to the window frame. Add 20–30mm overhang at the front for a neat finish.
Step 3 — Cut the Board to Width
Cut the board to the measured width. If the window recess has angled reveals, cut the ends at the appropriate angle (typically 90° for square reveals).
Step 4 — Cut the Horns (if required)
If the board extends past the window reveal, cut small notches (horns) at each end to sit flush against the wall.
Step 5 — Dry Fit and Check Level
Place the board in position and check it's level. Pack underneath with timber offcuts if needed.
Step 6 — Fix in Place
Apply grab adhesive to the underside and press firmly into position. Hold in place for a few minutes. For extra security, add a bead of caulk along the back edge where the board meets the wall.
Step 7 — Fill and Paint
Fill any gaps with decorator's filler, sand smooth, and apply your chosen paint finish.