repairing my fieldstone foundation with lime mortar in toronto (part 1)
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My downtown Toronto house was built in 1885. When I was re-routing my downspouts I noticed large gaps in my fieldstone foundation where the 128 year-old lime mortar had deteriorated into sand. To prevent rodent and water entry, and to stop stones from shifting, I decided to excavate and replace the failed mortar. This video gives an overview of the project.
I used the historically correct Natural Hydraulic Lime (NHL) 5 for the deep joint replacement, and NHL 3.5 for pointing. NHL is available from Kreitmaker (www.kreitmaker.com) in Toronto. Two local heritage masons kindly advised me on materials and procedures, as well as on local suppliers. One was from Hunt Heritage (http://www.huntheritage.ca), the other from Toronto Masonry Repairs (http://torontomasonryrepairs.com/).
The three most important things I learned were:
1) Flooded basement? Fix your roof before your foundation. In many cases (including mine) basement flooding is caused by problems with eavestrough drainage and leaking roofs. Before you pay someone thousands of dollars to put in weeping tiles and sump pumps, be 100% sure your roof is in good condition, your eavestroughs are clean, your downspouts are draining at least 1.5 meters from your foundation, and your soil slopes away from your house to allow water to run away from the foundation when it rains. Water in the basement can often be stopped entirely by correcting roof, eavestrough, and drainage problems. Often simply cleaning your eavestroughs can prevent basement flooding.
2) Never use Portland cement with old masonry. Portland cement-based mortars (sometimes called Ordinary Portland Cement, or “OPC”) are very actively discouraged for use with old brick houses and old stone foundations. Modern OPC is much harder and less absorbant than lime mortar. The hard OPC mortar causes old soft bricks to “spall” (i.e., flake off) from water retention and an inability to sufficiently expand and contract during freeze/thaw cycles. OPC mortar might look good for a while, but completely destroy bricks in fewer than 10 years. Here’s an article describing the differences between lime mortar and portland-based mortar: http://www.masonrymagazine.com/1-06/limemortar.html
3) Old foundations can be very shallow. Unfortunately, before I started digging, I did not know that old foundations in Toronto are often barely deeper than 1.5 meters. When I started excavating mine, I unintentionally dug approximately 20 cm below the foundation in a couple of places. As soon as I realized the error, I stopped, and had to replace the excavated areas with a small concrete footing to prevent settling. If you dig out your foundation for any reason, be very careful to start with a small test dig to determine the depth of the last stone. If your foundation is pre-1900, it may well have no footing at all.
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