How do I repair and maintain sills?

Most homeowners give very little thought to the maintenance of the sills (those stone or cement window sills) in their homes. They should pay attention, however, because splitting a sill can have costly consequences in the long run. Cleaning and repairing sills is a simple but necessary task.

In fact, if rainwater manages to seep into the cracks in your sills, it will gradually attack the stone or cement that makes up the sill and work its way behind the bricks under the window sill. Imagine the situation of accumulating hidden water and the cold weather arrives!

With the freezing and thawing cycles that we experience, the bricks or other masonry will then burst or create a humid climate on the interior wall that is conducive to the proliferation of mold, the main cause of allergies.

Example of a neglected sill

Friable material

“It is said that a prisoner with a spoon can patiently scrape through a cement wall and escape,” says Louis Verdy, winner of the City of Montreal’s 2002 Artisan Award, to illustrate the fact that cement is a brittle material.

In older homes, you will find mostly gray stone or granite sills, known for their hardness and resistance to frost. However, they are expensive. That’s why cement spandrels, which are very inexpensive, are popular. These come in one piece or in two parts. In the latter case, they must be attached to the center.

Siding, like other exterior components of a home, needs maintenance; exposure to sun, rain and snow causes deterioration. The appearance of surface mold is a sign of the danger of contaminating indoor air quality.


In housing, it is always better to repair than replace if you want to save money. This also counts for cleaning and repairing the sills!

“If you see a small crack on the spandrel, you need to apply a layer of cementitious polymer to the exterior.

Beforehand, you scrape off some of the cement or stone and save this residue for last. Once the polymer is applied, it is sanded again with sandpaper or a disc on the grinder so that it returns to its original appearance.”

Here are the easy tips from the experts, now it’s time to learn how to do it!

How do I repair sills?

The steps to clean and repair sills are easy, but essential; here are some of them:

    1. Surface cleaning with a specialized product, such as TexNov’s Surface Preparer
      1. This product comes in a concentrated format. Dilute one part product to three parts water.
      2. Pour the mixture into a clean spray bottle
      3. Spray on the surface.
      4. Leave for fifteen minutes
      5. Rinsing with a pressure washer (2000 lbs)
    2. Crack repair
      1. If cracks are apparent, please use a cementitious polymer, such as TexNov’s All Purpose Polymer.
      2. Sand the edges of the crack with sandpaper or a grinder equipped with a suitable abrasive disc.
      3. Clean up the dust and rinse with water.
      4. After drying, fill the crack up to the edge with the polymer and let it dry according to the instructions.
      5. Sand the sill to obtain a smooth and level surface.
    3. Rinse thoroughly with a pressure washer

Here are some pictures of our sill repair project

Blackened sill due to weathering
Pressure washing to remove surface dirt
The surface quickly recovers its original shine.

Tips for the proper cleaning of sills

You’ve learned that cleaning and repairing sills is essential to maintaining your home. The All Purpose Polymer will come in handy for future projects, so keep the extra. Small repairs to masonry surfaces such as entry balconies, cracks in your fireplace mantle, cracks in your garage floor are just a few examples.

If the masonry has deteriorated under the spandrel, also apply the All Purpose Polymer.

The all-purpose polymer comes in a two-component format.

Basically, this is a two-component blend of 100% acrylic resin and specialized aggregates with inorganic pigments, marble grit, quartz sand, silica aggregates, additives and high performance fungicides.

About the Surface Cleaner

For the Surface Prep, it must be said that it is a concentrated solution, so a liter bottle should be sufficient for this and other future projects. Try it also to clean your concrete balcony or even stone decorations in your landscaping; it will recover the original shine easily and in a durable way.

Last tip: make sure the sill is well supported on the bricks. Otherwise, the pressure may cause a new crack in the center of the part.

Find out how to repair a house floor with the following video:


Where to find the products?

The products listed in this article are available at most home improvement centers. Please use the map below to find the one nearest you:


      Although coatings are easy to install, we strongly encourage hiring a professional. TexNov inc. is not responsible for any work done without professional supervision. TexNov is easy to apply, but the easiest way is to have the work done by an expert. Cleaning and repairing sills is an easy project, but don’t overlook the steps outlined below.


      The original source of the text comes from an article that appeared in the newspaper “La Presse” on August 20, 2007.

      For more information, visit the following link:

      The images are from a recent demonstration project at TexNov Inc. All rights reserved.

      Did you find this article interesting? Check out our latest post: How to transform bathroom walls with microcement?