Replacing Concrete Paving Slabs

A small hole or crack in a concrete or stone windowsill can easily be repaired with the appropriate exterior filler or mortar. Damage to the edge or damage so extensive the whole sill needs replacing is more difficult to deal with. In both latter cases you will need to build shuttering (a wooden frame to hold the concrete in shape).

Remove any loose concrete and then fit the shuttering. It is a good idea to use the existing windowsill as a template to build the shuttering and if possible build it so that it can be attached to the wall on either side of the sill. Using dry ready-mix concrete, make your repairs and leave it to set. Once the concrete is completely set, remove the shuttering.

If you are making repairs to the underside of a sill, or if you are replacing a whole sill, you need to remember the drip groove running along the front underside edge of the sill. Without this, water will be allowed to seep back into the building by running under the sill. This can easily be achieved by having a length of rope or cord pinned to the bottom of your shuttering box.