Make your external windowsills look like new again by following a few, simple steps

by Mark Bennett

July 26, 2024

an exterior windowsill decorated with potted plants

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Exterior windowsills - especially when overlooking a courtyard or balcony - are an extra surface to place ornaments, potted plants or even useful tools. However, being exposed to the elements, exterior windowsills get dirty and stained very quickly. So how can you clean these windowsills properly? Here's some useful tips:

Regular cleaning of windowsills

The best approach is to clean the windowsills regularly and not ignore doing this chore for long periods: as stated, external windowsills get dirty very quickly and you need to stay on top of this.

A universally useful detergent - regardless of the material they're made of - is Marseille soap diluted in water: use non-abrasive sponges and remove all the debris that usually settles on windowsills and before it "concretizes". Marseille soap is delicate and can be used on all surface types.

For stubborn dirt and stains, you can scrub these with baking soda and a toothbrush (but not one with very hard bristles). Be sure to rinse the baking soda residue away completely and thoroughly afterwards.

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Removing stubborn stains and marks from windowsills

a mark left by a flowerpot on the marble surface of a windowsill

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When the above cleaning methods do not work on stubborn stains and marks, then you can try "stronger" remedies (but only infrequently):

  • Pressure washer: a jet of pressurized water (but not set to maximum power) is very effective in removing stains. Hold the nozzle at least 30 centimeters from the surface and move it slowly and evenly over the area to be cleaned. Be aware that, in the long run, this type of pressure cleaning slowly erodes surfaces, making them more porous and therefore more prone to getting dirty quickly again;
  • Hydrogen peroxide: for stains such as rust or for limescale build-up (which is often left by water dripping from flower pots), you can use hydrogen peroxide to remove these types of grime. Hydrogen peroxide is ideal for cleaning windowsills that are made of certain types of marble or travertine. That said, make sure to rinse the hydrogen peroxide away thoroughly after allowing it to act on the surface (typicaly 15 - 20 minutes).

Can vinegar, bleach or citric acid be used for this cleaning chore? Well, these substances are certainly very effective in removing many types of dirt, but they are also very aggressive. If you use them very rarely - once or twice a year, for example - they can be used sparingly. Keep in mind, however, that constant/regular use of these products will corrode standard windowsill surfaces.

What's your favorite method for cleaning your windowsills?

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