What Does Concrete have to do with Roof Leaks?

Did you know that your “roof” leak might actually be caused by deteriorated mortar joints in your chimney? If yes, congratulations! But many homeowners do not realize this is a major potential source of water leaking into your home.

Because we are on roofs every day we keep a keen eye on chimneys and exposed brick walls above the roof line.  They are always included in our roof inspections along with the roof itself, skylights, flashing, wall caps/parapets and gutters and downspouts.

So how do you go about properly re-pointing historic chimneys and brick facades in Capitol Hill homes?

Re-pointing describes the restoration of historic brick structures by removing mortar between masonry joints and replacing it with new mortar. Using the right techniques and materials are key to doing the job properly.

Methodology and Techniques

Historic brick structures of the type found in Capitol Hill, Georgetown and Old Town, Alexandria must be re-pointed in their entirety and not in sections; patching new mortar on old without chiseling away the old mortar is throwing money down the drain. Mortar bonds much better to the clean, chiseled surface of the brick.

Mortar joints should be struck with a tool creating a slight concave recess in the joint to prevent water penetration and staining on the brick façade.  A newly re-pointed structure should be cleaned thoroughly with a solution of diluted acid or a specially formulated masonry cleaner to remove dirt, staining and residual mortar left on the brick face during re-pointing.

Materials

Buildings built before the 1930’s generally have softer brick, which makes them a candidate for old-style lime mortar which is really the only way to go. Most older masonry structures were built using lime and sand including the Egyptian pyramids and 600 year old castles in Scotland.  The composition structure and level of hardness/softness are completely different from cement or concrete which are modern building materials best suited for new construction, not renovation of historic masonry structures.

If a building or chimney is re-pointed with cement the extreme density of the materials will cause the softer coal-fired bricks to crack and will eventually show signs of structural damage and interior water penetration. It is not true that “the harder the mortar the sturdier the wall” as some contractors would have you believe! Lime mortar containing NO cement is by far the best option and the only type that we use in our restoration work.

Many contractors use Type N or Type O mortar. While these mixes consist mostly of lime, they do contain some cement which, as  said, may harm your structure.  So, if you have had a previous patch job, which used masonry cement, and not lime-based mortar, the patch job will probably do more harm than good over the long run because the cement can dam the joints trapping moisture inside the brick. In winter water-logged walls can freeze and crack allowing still more water to penetrate the bricks. In summer, as the brick tries to expand, its protective skin can pop off. The bottom-line is that cement will hurt, not help your walls.

You need a contractor who will know how to chisel out the old cement mortar to a proper depth and use lime-based mortar and traditional re-pointing techniques.  You want your walls and chimneys to withstand the test of time like the ancient Pyramids and old Scottish castles!

Tom Daniel is the owner and General Manager of R. Thomas Daniel Roofing, a third-generation Capitol Hill family enterprise that has provided roofing services to Capitol Hill families for more than 90 years. He is a Hill resident and the company is the recommended roofer of Capitol Hill Village. He can be reached at 202-569-1080 or tom@rthomasdanielroofing.com. Visit the company website at www.rthomasdanielroofing.com.


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