Fixing your concrete sills: how to repair concrete wndow sills and more

Concrete window sills tend to be found on older properties, are subject to wear and tear over the years and may need repair. Whether you were informed that your concrete window sills need repairing by a Level 3 or Level 2 chartered surveyor or spotted the damage to your sills on your own, you must know how to fix the window sill correctly and not risk further damage. 

It does not matter if you are entirely new to DIY; repairing your concrete window sill is simple and easy with the right tools and guidance. If left untreated, a cracked window sill can allow water ingress, leading to possible damp issues. In this blog, learn how to repair concrete window sills and how you can make them last.

When looking for things to repair, the two main types of damage that you should look for are horizontal and vertical surface cracks. If left untreated, these can cause further damage and can be caused by weathering, thermal expansion, and structural issues. 

Spalling is the flaking of concrete surfaces, commonly caused by water seepage that leads to corrosion of the steel reinforcements. This will lead to the concrete breaking off and causing patches to appear. 

Other issues that can cause or lead to damage are:

• Discolouration - A change in the colour of the window sill, potentially indicating water damage or mould growth. 
• Warping - If your window sill looks warped or bulging, it may indicate internal structural issues. 
• Chalking - If you find a chalky residue on the window sill, then the concrete may be beginning to disintegrate.
• Crumbling - If the concrete feels soft to the touch or crumbles away quickly, it is a clear sign of degradation.  

Before you begin repairing your concrete window sills, it is important to know how to prepare the sill so that the repairs remain in place after the job is completed. 

To ensure your repairs are done correctly and will hold after completion, you should ensure the work surface is cleared of debris. You can use a brush to sweep the damaged areas and rid the affected area of any loose concrete. 

Sand the area down with sandpaper to make it even. This is a great way to prevent bulging later on if water cannot get into an uneven surface. 

Finally, give the window sill a rinse-off to clear the surface of any debris you have brought up and leave a surface ready to be worked on. Allow it to dry completely before you go about any repairs.

Any cracks in the sills should be carefully repaired using epoxy mortar. If applied correctly, the epoxy mortar will set and last for many years. Once dried, you can easily paint over the mortar and return the sills to pristine condition. 

Epoxy mortar is ideal for quick and durable repairs and will adhere to most substrates, including concrete, masonry, bricks, steel, or other materials. The result is an extremely hard-wearing finish that can withstand time and harsh conditions.

Repairing your window sill does not need to be stressful. If you are unsure whether your window sills need repair, consult one of our RICS surveys. A surveyor will survey your home and inform you of all the faults and defects with the property, including any issues with your concrete window sills. 

If you want to sell a house, a property surveyor will help you get your house in the best state to get the most for it. Similarly, if you are buying a house, our surveyors will help you find out the issues with potential properties, allowing you to get a true reflection of the property's value. 

Be sure to contact us if you have questions about our RICS surveys or other services. At Surveyor Local, you can find out all you need to know about repairing your concrete window sills and more.