How to Stain Window Sills

Remove old paint or other finish from your window sill with a paint scraper and 70-grit sandpaper. Sand your window sill again with 100-grit sandpaper until it is smooth.

Vacuum the area around the sill and the window sill itself to remove dust and other debris. Wipe the window sill with a clean cloth and denatured alcohol, available from most hardware stores, and allow to dry.

Cover all areas of the window and wall immediately next to the window sill with masking tape. This will shield any areas you do not wish to stain from accidental splatters and drips.

Open and stir your wood stain with a stick until you achieve a smooth, even consistency. Dip a good-quality bristle brush into the stain and allow the bristles to soak it up. Brush the stain liberally onto the window sill.

Wipe off the stain lightly and rapidly with clean cotton cloths or rags. The longer you allow the stain to stay on the wood before wiping, the darker it will become. Reapply the stain in any areas where the stain becomes too dry or sticky to remove.

Brush any areas of the sill, such as corners, that the you couldn't reach with the rag with a clean dry paint brush. Clean the brush on an old newspaper between strokes so that it remains dry.

Examine your stain finish. Brush spots that appear too light and wipe again. Wipe any spots that appear too dark with a rag dampened with paint thinner. Allow the stain to dry for 12 hours or according to the manufacturer's directions.

Open and stir your translucent acrylic varnish with a stick until you achieve a smooth, even consistency. Dip a good-quality bristle brush into the varnish and allow the bristles to soak it up. Brush lightly onto the sill. Allow the varnish to dry according to the manufacturer's directions.

Sand down the sill lightly with 220-grit sandpaper until the surface is smooth and wipe with a clean cotton cloth and denatured alcohol. Apply another coat of varnish and allow it to dry before removing the masking tape.