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When rain infiltrates, the ends of a masonry window sill may burst and become detached as soon as the first frost breaks. If the rim is slightly damaged, local repair is possible.

Gradient window support

A window sill is used to evacuate and return rainwater to prevent it from running down the wall.
During construction, whether the support is prefabricated or poured in place, the reinforcement of the concrete may not have been extended far enough to the ends (ears).
If one of them breaks, a local repair is possible without having to completely replace the masonry. Simply reinforce the anchor in the wall and take the shape of the edge. An operation that requires precision, but which guarantees a good seal.

Evaluate the damage

Broken end of a window sill

  • Evaluate the damage by checking the underside of the window sill, which can also be degraded.
  • Detach and purge the non-integral parts with the chisel.

Reinforce the frame

Drilling the support to the concrete drill

  • Drill a few holes of 8 mm in the thickness of the support and in the wall.
  • Clear a reservation sufficient to reinforce the frame.

Inserting screws to extend the reinforcement

  • Insert an ankle into each hole.
  • Place 6mm screws (or appropriate length) to complete the missing reinforcement.

Organize the cofffrage

Wooden formwork for masonry window sill

  • Make a small formwork in boards for the ears.
  • Attach a 10 x 10 mm cleat to recreate the drop of water (or drip) under the support.

Verification of the plumb of the formwork at the level

  • Set up the formwork by holding it with a clamp.
  • Screw the front board flush with the support.
  • Check the plumb level.

Filling the formwork with concrete

  • Fill the reservation and the formwork with a little concrete and then cement mortar.
  • Pack well and smooth with cat-tongue trowel.

Correct imperfections

Application of a coating with a spatula

  • Dispose after drying.
  • Scrape imperfections on recovery, then apply a special exterior coating to the spatula.
  • Smooth the edges perfectly.

Application of the finishing coating

  • Let dry for several days under cover (plastic protection).
  • Apply the finishing coat (here, a Pliolite facade paint).


Video Instruction: Renovate, repair and paint your windowsills using StoneLux Windowsill Stone Coating