How to Clean Window Sill Mould

Last update: 4 months ago


Constant condensation on your windows is a prime reason for window sill mould. It easily turns into a tenacious problem that has the potential to throw into despair even the most composed homeowner. Yet, despite the solution being time-consuming, it’s highly effective. Here’s the how-to:

The basic things you need for cleaning mould off window sills are:

  1. Gloves
  2. Bleach
  3. Rag
  4. Brush
  5. Plastic Tarp
  6. Garbage bag

Depending on the amount of mould and the time you’ll spend cleaning, you might need some more tools and even some safety gear. If the sills are made of wood, you’ll also need:

  1. Goggles
  2. Dust mask
  3. Sandpaper
  4. Paint
  5. Paintbrush

You can replace the bleach with:

  • Vinegar and ammonia solution;
  • Vinegar and baking soda solution – even though it’s not effective after several minutes, its initial reaction is strong enough to deal with mild mould;
  • Dishwasher soap;

How to Clean Window Sill Mould


  1. Equip your safety kit – first off, make sure you won’t accidentally burn yourself with the acidic detergents. Put on rubber gloves to protect your hands. If you prefer to be extra careful, a pair of glass goggles from the convenience store will do the job. You never know how much mould has accumulated and how long you will have to scrub it off.
  1. Safe-proof the cleaning area – in order to avoid splatters all over the place, put a plastic tarp or a large garbage bag under the window you are going to clean. The tarp is more advantageous since it can be positioned stationary on the ground, but if you don’t happen to have it, you can use a rubbish bag as well.
  1. Let air in – before you tackle the dirt, open the windows and ventilate the place. This way some of the mould spores will fall outside. Leave it open for the whole cleaning and then some – this way the detergent fumes will disappear as well.
  1. Mix your cleaning solution and start scrubbing – pure bleach will be too strong, even if the mould stains have been quite persistent. Therefore, dissolve one part of bleach in three parts of lukewarm water. Dip the brush into the solution and scrub away the mould. Afterwards, wipe away the scraped particles with the rag.
  1. Dry and wipe – take some time for the window sill to dry out and then scrub off the mould that’s still hanging there. Use the rag, dipped in clean water. Before you close the window, make sure you left the sill to dry completely.
  1. Sand the window sill – if it’s made of wood, then you have to use a sandpaper to scrape the last remaining black mould. Remove the sawdust with your vacuum cleaner. It will take more time if the wood has been painted beforehand – you’ll have to prime and repaint it in order to completely restore its initial appearance.
  1. Dispose of the safety gear – remove the plastic tarp, fold it so that the dirt won’t fall off and throw it out in a garbage bag.

Prevent the Mildew to Build Up Again

Even if you manage to clean it this time, if you don’t take any precautions, the mould will slowly take back the lost territories. Therefore, make sure to keep the sills dry at all times, or at least whenever it’s possible. For example, if you apply caulk on the window edges, it will prevent any leaks from the outside environment and will deal with condensation drops right away.

Window Cleaning in London

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