18mm primed MDF window board with a rounded bullnose edge, supplied in a 4.2m length at 300mm wide. Also known as an internal window sill, it gives a clean, modern finish to window reveals and is easy to cut to size on site. The factory-primed surface is ready to paint to match your décor.
Our bullnose window boards are made from 18mm MDF with a smooth, factory-primed finish and a fully rounded front edge. MDF (medium-density fibreboard) machines cleanly and has no knots or grain to show through paint, giving a smooth finish that solid timber boards can struggle to match. At 300mm wide, the board is deep enough for most standard UK window reveals and can be ripped down for narrower openings. The 4.2m length lets you cut several sills from a single board, or run one continuous, joint-free board across a wide window. The primer acts as a sealed base coat, so once fitted the board only needs a light sand and a top coat of paint.
Cut the board to length and notch the ends so it sits into the reveal, tight against the window frame. Fix it level with grab adhesive or screw down into timber battens, then seal the joint to the frame with flexible sealant or decorator's caulk, all available in our Sealants & Adhesives range. Prime any cut edges, lightly sand the surface and finish with two coats of hard-wearing paint.
A bullnose window board is the flat shelf that sits inside the window reveal, often called an internal window sill. The bullnose refers to the fully rounded front edge, which looks softer than a square edge and is less likely to chip or catch.
In everyday use, yes. Technically, the window sill is the external part of the frame that sheds rainwater, while the window board is the internal shelf. Most people call the internal board a window sill, and that is what this product is for.
Yes. 18mm MDF cuts cleanly with a fine-tooth handsaw, circular saw or track saw. The 300mm width can be ripped down for narrower reveals, and the 4.2m length is enough for several standard windows. Seal any cut edges with primer before painting, as raw MDF absorbs paint quickly.
Yes. The primer is a base coat, not a finished surface. Give the board a light sand, wipe off the dust, then apply two coats of a durable paint such as satin, eggshell or gloss. A hard-wearing finish is best, as window sills often have plants, ornaments and condensation to deal with.
Yes, MDF is one of the most common materials for internal window boards. It is stable, smooth and takes paint well. The main thing to watch is moisture, so make sure every face and cut edge is sealed with paint, and wipe away heavy condensation rather than letting water sit on the surface.
Cut the board to length and notch the ends so it fits into the reveal and sits tight against the window frame. Fix it level using grab adhesive or screws into timber battens below, then seal the joint to the frame with flexible sealant or decorator's caulk before painting.
If the board turns out to be moisture-resistant MDF, update the fifth answer to lead with that. It's a strong selling point for kitchen and bathroom windows. Make the same edit in the schema.
