Ask the Expert 
Window Sills
QUESTION: I'm handy, but my husband isn't, and our home is 12 years old. I've been replacing the caulking around my exterior windows, and I recently watched a home improvement show that said the window sills - mine are two long bricks with cement between them - should have caulking between them. Is this true?
-- Jackie from Burlington, ON
ANSWER:
Yes, Jackie, this is true. Window sills are subjected to a lot of water run-off from the glazing above. Unlike brick, which absorbs precipitation, window glazing is impervious and will shed rain or snow. This results in a lot of moisture run-off to the sill below. If joints in the sills aren’t sealed, water can penetrate the wall cavity, potentially resulting in rot and mould and eventually, structural damage.
The reason caulking is the best option for these joints is that it doesn’t absorb water the way regular mortar does, and maintains some flexibility with the changes in temperature throughout the year. Be sure to clean out all the old caulking or mortar, and choose a high quality exterior caulking designed for masonry. Fortunately, exterior caulking is available in a variety of colours to match most brick and sills.
Expert's Bio
Charles Bull manages a design build construction company in Toronto, Canada, spending his days looking into everything from permits to the latest green building methods. With more than 15 years of experience in residential real estate, construction and renovation under his belt, Charles knows the answers to your home renovation queries — or will find them out if he doesn’t!
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