How to paint windowsills

Windowsills have a tough job to perform. Inside they create a focal point for that perfect view, or provide a display shelf for photo frames and plant pots. Outside they endure all weathers, while adding to your home’s kerb appeal.

Like all DIY projects, the best results are achieved when time is taken to prepare a detailed plan. 

Pav Wąsik, founder of Uptown Interiors, shares his expert tips on how to paint a windowsill and achieve a high-end finish.

Tools checklist

Interior windowsill

• Dust sheet
• Fine-grit sandpaper (220-grit)
• Wood filler
• Primer
• Interior wood paint 
• Brush (or roller)

Exterior windowsill

• Low tack masking tape
• Coarse sandpaper (80-grit)
• Power sander
• Fine-grit sandpaper (220-grit)
• Spare wood for filling
• Exterior wood paint
• Brush (or roller)

1. Protect floors and furniture

If painting inside, Wąsik says: “Cover the floor with a dust sheet to protect it from paint splatters.”

While you won’t have the issue of paint getting spilt on carpet or furnishings outside, he still recommends protecting the surrounding area.

“Use low tack masking tape to cover the adjacent surfaces, such as the wall, glass, or window frame, to prevent accidental paint splatters.”

2. Seal the cracks and mend the rot 

You’re unlikely to find a rotting windowsill inside, but you might find some gaps or cracks that need filling. If you do need to fill in a few holes, use a suitable wood filler.

Wąsik advises: “Follow the instructions provided with the filler to apply and shape it. Allow it to dry according to the manufacturer's recommendations, then sand it smooth if necessary.”

You can expect to carry out a bit more repair work to an outside windowsill, especially if it’s had a battering from the weather or been left untreated for a while.

“Inspect the windowsill for any signs of rot or decay”, says Wąsik. “If you find any, carefully remove the affected wood and replace it with a matching piece. Sand the repaired area to ensure a seamless finish.”

3. Give the surfaces a sand 

Whether you leave your interior windowsills bare or adorn them with your treasured items – causing extra wear and tear on the paint work – they will need to be sanded down. 

“For inside, use a medium-grit sandpaper, such as 120-grit, to sand the surface of the windowsill.” says Wąsik. “This helps create a smooth and even surface for better paint adhesion. Then, wipe away the dust with a clean cloth.”

The exterior windowsills will need a slightly different treatment, as the paintwork will be weathered.

“If the windowsill has rough or peeling paint, you may need to use a coarser sandpaper, such as an 80-grit or a power sander to remove the old paint. Sand until the surface is smooth, and then wipe away the dust.”

4. Apply primer for the top coat

“Primer is not always seen as necessary, but it does improve paint adhesion and provide better coverage, especially for bare wood or stained surfaces,” says Wąsik.

“I always recommend applying a thin, even coat of primer using a brush or roller, following the manufacturer’s instructions. Allow it to dry completely before proceeding.”

5. Apply paint with small, even strokes 

Wąsik recommends using a high-quality paintbrush or a small roller to apply the paint.

“Dip the brush into the paint about one-third of the bristle length, tapping off any excess paint against the edge of the paint tin.”

Once you’ve loaded the paint on to your brush, you can get to work.

“Start at one end of the windowsill and work your way towards the other end, using smooth and even strokes,” says Wąsik.

“For the best finish, paint in the direction of the grain – if the windowsill is wood – or follow the contours of the surface."

6. Wait for the paint to dry

“The drying time can vary depending on the type of paint used and the environmental conditions,” says Wąsik. If it’s a warm, sunny day, your windowsills will be ready to recoat sooner than if the temperature is on the chilly side.

“It may take anywhere from two to four hours for the first coat to dry, but follow the manufacturer’s instructions for specific drying times,” Wąsik recommends.

7. Apply a second coat

“When the first coat is completely dry, inspect the windowsill for any missed spots or uneven areas. If necessary, lightly sand the surface with a fine-grit sandpaper, such as 220-grit, to smooth out imperfections,” Wąsik advises.

Once you’ve checked over the surface, you can then apply a second coat of paint following the same technique as before. Then allow it to dry completely.

8. Clean your brushes and seal your paint tins

Once you’ve finished painting your windowsills, it’s good practice to clean up properly and extend the lifetime of your tools. Firstly, start by making sure your paint tins are sealed tightly. This will prevent any air getting inside and drying out the remaining paint.

“Wipe off any paint drips or smudges from the outside of the can to keep it clean,” adds Wąsik. 

“Store the paint tin in a cool, dry place away from direct sunlight and extreme temperatures. If possible, keep the paint tin off the ground to prevent rusting. Make sure it is stored in an upright position to avoid leaks or spills.”

Your second job is to clean your paint rollers and brushes – this will ensure they’re in good working order the next time you’re ready to paint.

“How you clean paint off your brushes, depends entirely on what kind of paint you are using. Some may just need water, whereas others will need specific solutions. 

"Always check the paint tin for specifications on brush-cleaning and prepare this before you start so you’re ready,” says Wąsik.

Size up your brushes 

Using the best tools for the job will make the task easier and the result better. Here Wąsik advises us on how to choose the best paintbrush for painting a windowsill.

• Consider the size - Choose a brush size appropriate for the dimensions of your windowsill. As a general rule, a 2-inch (5cm) brush is suitable for most windowsills and will provide good control and coverage.
• Opt for an angled sash brush - An angled sash brush, also known as a cut-in brush, can be helpful for painting corners and edges of the windowsill. The angled bristles allow for more precise application and better control.
• Choose the right brush for the paint type - It’s also important to consider the type of paint you are using. Some paints, especially oil-based ones, require specific brushes. Check the manufacturer’s recommendations to ensure you have the appropriate brush for the paint you are using.

What kind of paint do you use on windowsills?

The paint you choose can have a big impact on the result – it’s therefore wise to get to grips with how different paints work and perform, so that you make the right choice. It’s always worth buying a high-quality paint, as it will reward you with greater dividends.

“It will provide good coverage, durability, and resistance to wear and tear. These paints typically have better pigments and binders, resulting in a longer-lasting finish,” Wąsik explains.

Questions to ask when choosing windowsill paint

Are you painting inside or out?

If painting an exterior windowsill, opt for an exterior paint rather than trying to get by with one meant for interiors. They are formulated to withstand outdoor elements like sun, rain, and temperature fluctuations, while interior paints are only designed for indoor use.

What material are the windowsills made from?

The surface you’re painting will also determine your choice. Windowsills are made from various materials, such as wood, metal or composite. Select a paint that is suitable for the specific material of your windowsill – for example, an exterior paint designed for wood if you have a wooden windowsill.

What look do you want?

Another aspect to consider is the finish you’re after. Think about the desired look and functionality of your windowsill. For a glossy finish that is easy to clean, opt for a satin or semi-gloss paint. If you prefer a less shiny appearance, choose an eggshell or matte finish.

Do you need to protect against mould or discolouration?

Some paints offer additional features such as UV resistance, mildew resistance, or quick-drying properties. Evaluate your needs and select a paint with the appropriate features for your windowsill.