Painting Exterior Windowsills – A Full Guide

Updated Jun 6, 2024 | Posted Aug 13, 2023 | Professional insight, Product Advice | 0 comments

Painting exterior windowsills will not only add to the aesthetics of a building, but it will also go some way to protecting them from the elements. In this blog, I’m going to talk through the important points of painting masonry windowsills and the best products you can use.


The Prep


I’m sure you’ve heard the old saying, “prep is 90% of the work when decorating”. Well, I don’t agree with that, but it is important. If you don’t get your prep right, then your freshly painted windowsill will not look good for very long.

Previously painted windowsills should be abraded with aluminium oxide and any loose paint should be scraped off. Bare masonry does not need to be primed unless it is grainy or chalky, or the existing paint is peeling in patches.

Assess your windowsills. If you think you do need a primer, then go with Zinsser Peel Stop. This is more of a stabilising solution, which is designed to penetrate deep into your windowsill, stabilise any unsound masonry. It will also stick down the edges of any previous paint where it has peeled and prevent it from peeling further.

It doesn’t matter how good your paint system is, it won’t last if the paint system underneath it starts to fail. So, if in doubt, prime or spot prime with Zinsser Peel Stop.

Imperfections, be it surface, or deep repairs will need to be filled. I have tried many masonry fillers over the years, but the best I have found is Toupret Rock Solid Filler (also know as Murex). You can use this filler to any depth of repair on your windowsill, but it is also good for skimming over surface indentations.

The one downside of using this filler on exterior windowsills is that it is hard to sand down, so don’t over-fill if you can help it. However, you shouldn’t need to. If you mix it to the right consistency, it is easy enough to work with. Once cured, it will last for many years.

Painting Exterior Windowsills


I can give you a few tips on painting your windowsills. The first is to use a good quality trade paint, which I’ll get into later. This is important for longevity.

Dilute your paint slightly for the first coat. This will help with ease of use and adhesion. If diluted, the paint will absorb slightly into any filler or bare masonry on your windowsill and seal the material.

Paint right up to the edges of your windowsill and work the paint into every little gap. This will not only look better, but it will also help seal the windowsill and protect it from moisture, meaning your paint finish will last longer.

Speaking of sealing the moisture out, make sure you paint the underneath of every windowsill, even if you can’t see that edge. Miss this, and when it rains the water will run down the front of the windowsill, track underneath it, then get absorbed into the stone. Water in your windowsill will cause the paint to fail, so don’t skip the parts you can’t see.


The Best Paint for an Exterior Windowsill


There are a couple of things to consider when choosing the best paint for exterior windowsills. If the substrate contains any moisture (which isn’t ideal for the reasons I have already mentioned), then the best option is an oil-based pliolite masonry paint. However, water-based is fine 90% of the time.

I’ll give you 3 recommendations, all breathable so will cope with a certain amount of moisture. I’ll give you a premium (and expensive) option, a good quality, but reasonably priced option, and an oil-based option. Just choose the paint that best suits your needs.


Emperor Paint Masonry Paint

This is the premium option, and easily the best paint I can think of to coat exterior windowsills. It is silicate-based, which makes it very breathable. It also has hydrophobic technology, which basically means it repels water.

Emperor Paint also goes some way to retaining heat, which may not make a huge difference on exterior windowsills, but it’s fantastic on rendered walls. The lifespan of this paint is great too, simply because they use the best resins available. Use code DFUK at the checkout for a little bit of discount.

Armstead Trade Masonry Paint

This is the “good trade paint at a reasonable price” option. I love Armstead masonry Paint, especially on exterior windowsills. The opacity, ease of use, and overall finish are brilliant. You can buy this paint at any Dulux Decorating Centre, but it’s normally cheaper to buy it online (it’s easier to get the colour you want too).

One of the things I like the most about this paint is that it is so easy to achieve a good finish on exterior windowsills. Avoiding brush marks and keeping a wet edge is made simple, so even a novice painter will achieve good results.

Zinsser AllWeather Masonry Paint

This is the pliolite (oil-based) option, so you might use it in challenging weather conditions, or when you need to stop stains from coming through the masonry.

I used this paint recently to paint a load of exterior windowsills on a house in my local area and loved it. I found it a lot easier to work with than most other pliolite-based paints, which helps when striking sharp lines. The drying time on this paint is quite quick too, so you can get multiple coats on your windowsills in a day.

Final Thoughts


I think that’s everything on painting exterior windowsills. We’ve covered prep, primer, and the best paint. Stick with everything I have said, and you can’t go wrong. Not just in the short term, but you’ll get that long-lasting finish.

Updated Jun 6, 2024 | Posted Aug 13, 2023 | 0 comments

About the Author

About the Author

Mike Gregory is a Professional Painter and Decorator who works in the Northwest of England. He mainly sub-contracts for large decorating firms and works on a wide variety of projects.
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