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Masonry/Brick Laying/caulking flagstone to house


Joan, I just had a wood staircase torn out going up my front steps and replaced with stone steps.  On one side of the entry way, which receives a lot of roof runoff during rains, the face board was rotted. I had it replaced and sealed up good. The outer layer over the new face board is a special waterproof sheet the outside surface is basically an asphalt shingle look. The mason butted the flagstones up against this material. It is about a 4' section. My shingles that will go on next are hand cut cedar shakes which will stay above the flagstones about 1/4 inch to prevent dirt from collecting in the gap and allow cedar shake bottoms to dry out after rain. I am thinking that prior to having the cedar shakes installed I should run a bead of caulk to cover the gap between the flagstone and the asphalt waterproofing sheet.   I would like your opinion on whether this is the correct method to do in this situation? Thanks, Jack

Thank you for your question Jack.

You are on the right track if you consider installing a caulking joint between your flagstone and the waterproofing sheet. Best to take all the precautions necessary, especially for areas where there is much water exposure. I would also recommend that you choose a caulking that is the same color as the mortar joint.

For your information, the same procedure is used for chimney installations. I know that many bricklayers install caulking on the gaps between roofing and the brick just to make sure there is no water infiltration, then they install a shingle over that.

Hope this information helps, and good luck with your project.

Best regards,

Joan Miller

Masonry/Brick Laying

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Joan Miller


Bricks and Stones have always been my passion. There are thousands of products to choose from and to learn about. If you need to know the specifics about bricks and stones, I will be more than happy to answer any questions about the masonry world as in how it is made, how to install it, specifications and quality.


I have been employed by brick and stone distributors for the past 25 years, meaning I have access to all sorts of information provided by the manufacturers that enables me to guide homebuilders and architects to make the best choice for their projects.


Masonry Specialist. Commercial and Industrial specialty.

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