How To Repair Water Damaged Indoor Windowsill: 8 Easy Steps

Whether you have guests over or not, it plays to your advantage to know how to repair water damaged indoor windowsill. If a windowsill is not properly protected from the elements, or if a wet mug is merely placed on the sill without a coaster, the sill will deteriorate or decay over time. 

A water-damaged window sill, on the other hand, can be restored to its former glory with only a little know-how. Water stains can be removed with toothpaste and baking soda, or rotting wood can be repaired with epoxy primer and wood filler, which is a more labor-intensive technique.

how to repair water damaged indoor windowsill


What Causes Water Damaged Indoor Windowsill

Rainstorms, humidity, fog, and hail can all cause your window sill to deteriorate. If left unchecked, rotten window sills can cause more serious problems than just lowering the value of your home.

If your window sills are made of wood, mold may grow on them. In which case, you might want to take a read on how to clean mold from window sill easily

The longer you wait to address this, the more possible your window sills will give way and tumble or split apart.


How To Restore Water Damaged Indoor Windowsill

You might want to check into some of the following options if you have substantial damage that can be fixed.

Step #1. Remove the paint from the window sill where it has been damaged with a paint chipper.

Step #2. Using a chisel, remove any rotten spots. Make careful you don’t go all the way through the wood because you’ll have to plug in the holes later.

Step #3. Using fine grain sandpaper, smooth off the window sill. Ensure that all splinters are removed.

Step #4. Begin scoring the holes you’ve made with a chisel or rough grain sandpaper; you’ll need to produce roughness to improve adhesion. Remove any sanding or chiseling dust.

Step #5. Apply a coat of wood-safe epoxy primer to the parts of the window sill that will be filled. Allow the primer to dry before proceeding.

Step #6. Get wood epoxy filler and observe the manufacturer’s mixing, pouring, and curing directions. To keep the sill as level as possible, pour over any hollowed areas.

Step #7. Sand the whole sill with fine grit sandpaper once it has cured. Remove any leftover dust with a damp cloth.

Step #8. Prepare the window sill with an oil-based primer, then paint as needed. Make sure to use a paint that can be used outside.

If the damage is to an indoor window sill, the procedure is the same, with the exception of one extra safety step. When applying epoxy indoors, it’s especially necessary to wear a respirator mask because the procedure can generate dangerous gasses.


How To Repair Indoor Window Sill If Rotten

You will, of course, need a replacement to the trim. You can, nevertheless, add a few extra stages.

Step #1. With a chisel, cut the entire piece of bad trim.

Step #2. Get a new window trim in the style and size that you want.

Step #3. Measure the dimensions of your window where you will be replacing the trim. Make a note of your measurements and transfer them to the new components.

Step #4. Make the cuts where you’ve marked them. Cuts for trims are usually 90 degrees, although checking the rejected piece and using it as a template can be helpful.

Step #5. Seal the area where you want to bond the new trim with latex caulking, then slip in the fix.

Step #6. Use nails or a nail gun to secure the new trim, then fill in the nail holes with wood filler or another solution of your choosing.

Step #7. Refinish and repaint the trim.


How To Refinish Window Sills

The style you want to achieve when refinishing wooden window sills is entirely up to you. However, it is often recommended that you begin by sanding the window sill with fine grit sandpaper.

After that, you can apply a wood-safe primer to improve paint adhesion. Use outdoor paint and apply two coats at the very least.


How To Re-Stain The Window Sill 

If you have the original stain color, staining your window sills and sashes is as simple as applying the stain, letting it sit for a few minutes, and then wiping away the excess.

If you don’t have the original stain color, you’ll have to choose between two options.

The most straightforward method is to take a piece of trim from your home and take it to a paint store for a custom match. We prefer to remove a small piece of trim from a closet that is out of sight. You can use liquid nails or any other adhesive to replace the trim.

The second choice is to make your own bespoke match. This is something most people do frequently, but it is also recommended to have a big stain kit with a variety of colors, pigments, and dyes. 

As a result, this is unlikely to work for everyone.

You can also rely on your eyes to determine the color. Many homes are stained in popular stain colors like Golden Oak.

Give this a try if you think your color might be one of these typical stain hues. Finally, to give your windows its best look, try to learn how to cover windows without curtains.



It is best to know how to repair water damaged windowsill to prevent mold infestations in the future. It’s either you just sit pretty or make yourself well-equipped with knowledge now.

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