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Expert Guide to Painting Outside Window Sills

Your exterior window sills play a crucial role in protecting your home. Not only do they provide structural support for window frames, they also prevent water from leaking into your home and absorbing into your walls, and stop cold chills from getting in.

Formulated to create a weatherproof and waterproof barrier to protect your home against the elements, our Dulux Weathershield range is the best paint to use for exterior window sills. While interior window sills tend to be wooden, most outdoor ones are made of concrete or stone, and we offer specific products for the best results on different surfaces.

Follow our step-by-step guide to refreshing your outside window sills with our exterior paints, with a breakdown of the tools and equipment you’ll need for this project.

How to paint exterior window sills and frames

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)

Step 1: Lay down dust sheets and mask off areas

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.

Step 2: Remove dirt and flaking paint

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.

Step 3: Fill any gaps

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

Step 4: Remove stains

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.

Step 5: Prime

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.

Step 6: Paint the first coat

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.

Step 7: Second coat and finishing touches

Once the first coat is dry, paint your second layer and give it another four hours to dry before removing any masking tape you’ve applied around the area. Your window sills should now be looking pristine and clean, and will have given your home an overall refresh.

Now that your transformation is complete, use with Dulux Weathershield paints to protect and perfect your window frames too. Check out our exterior inspiration hub for more helpful advice, plus colour ideas and the latest trends.