Expert Guide to Painting Outside Window Sills

Tools you’ll need 

When painting stone or concrete window sills, you’ll need the following tools and materials:

• Dust sheet
• Fungicidal wash (if the concrete on your window sills has mould, algae, moss or lichen)
• Sponge
• Coarse sandpaper
• Scraper
• Cloth or brush
• Masking tape
• Paintbrush
• Dulux Weathershield Stabilising Primer (optional)
• Dulux Weathershield All Weather Protection Smooth Masonry Paint (for a smooth finish) or Dulux Weathershield All Weather Protection Textured Masonry Paint (for a textured finish)

This can be a messy task, so before you start painting your outside window sills, lay dust sheets down underneath the areas you’re working on to avoid paint drips and splatters – this includes taping sheets to the wall underneath your window sills. You should also tape near the edges of where you’ll be painting to prevent any staining. 

When painting your concrete or stone window sills, it’s important to thoroughly sand down the surfaces that you’ll be working on using coarse sandpaper to ensure the results are as smooth and bump-free as possible. Remove as much old paint with your sandpaper and scraper as possible, particularly any flaking paint, as painting over this will leave an uneven finish. Then dust the surfaces with a cloth or brush.

Use an appropriate Polycell Polyfilla product to fill any gaps or dents in the stone or concrete.

If there is mould, algae, moss or lichen on the concrete window sills, use a suitable fungicidal wash and sponge to treat the area. Wait until this is completely dry before moving on to the next step.

If your surface feels chalky after the previous steps, it’s time to apply a single coat of the Dulux Weathershield Stabilising Primer to the window sill using a clean paintbrush. There’s no need to do this if you are working on new or bare surfaces.

Leave the primer to dry for two to four hours before moving on to the next step.

Stir the paint thoroughly in its tin. Then, take a clean paintbrush and paint your first layer of masonry paint on your window sills before leaving four hours for it to dry completely.

Top tip: Ensure you don’t have too much paint on your brush to avoid bubbles and an extended drying time between layers.