Wet Basements and Masonry… FAQ Friday with Randy Ruth

Basements are notorious for moisture problems. Mold can spread quickly and cause serious health problems throughout a home. Here is another frequently asked question from Randy Ruth about basement moisture and masonry.

Q: I am having moisture issues in my old stone farmhouse, especially in the basement and I’ve noticed a few places where mold appears to be growing. I was told it could be because of the masonry but I don’t understand how that’s possible?

A: It should be noted that most old stone farm buildings were primarily build with lime mortar, especially before 1900. The source of for the lime used during its construction would have been local and probably made in a kiln on the side of a hill, by an experienced lime burner. What all this means is that the mortar between the stones would most likely be soft, with an affinity for water and have relatively good vapor exchange. Those characteristics are quite the opposite when compared to today’s Portland Cement based mortars.

Moisture from old stone walls can occur on the inside a building and can predominantly be evident in the basement. Accompanying the moisture can be mold, which can result in a decrease in indoor air quality and overall health. Such a problem should be addressed accurately and swiftly to minimize health risks. In order to identify an approach to this problem more information needs to be gathered and thought about.

Was there any recent work done to the exterior of the building?

Sometime when a non-breathing sealer or cement render is applied to the exterior of an old breathing building, natural moisture inside the wall can become trapped. When moisture becomes trapped inside of a wall it will travel to the point of least resistance. Often times this is the interior of a wall resulting in excess moisture accumulating on the wall. The excess moisture, typically above 20% can create a breeding ground for bacteria so long as there is a food source.

If paper faced drywall was installed on the interior of the building accompanied by such exterior work, then the moisture can not only deteriorate the gypsum in the drywall but also give the bacteria a food source. The bacteria resulting mold on the surface can consume the paper face of the drywall.

Has the landscaping around the exterior of the building been changed?

Down spouting and improper detail to appropriate grading can also be a culprit in moisture ingress. If water is pooling in areas and not being carried away from the building appropriately, excess water can penetrate the stone wall to the point where it is noticeable and cause mold problems.

The point here is that something has probably changed in or around the building in recent years to allow excess water in the building. There are many different remedies for water ingress for historic buildings, all of which have some merit and may be appropriate depending on the specific issue. However, complete and proper excitation of a good remedy is always crucial to success for any project.

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