It is well established that the majority of masonry-related issues in a heritage building can be traced back, at least in part, to water infiltration, and its long term effects on the building fabric. Excessive moisture can break down the lime component of some lime mortars, ‘washing out’ the joints and depending on where water is entering the building, this may happen from the inside out. In addition, frost damage caused by water allowed to accumulate in the core of a masonry wall can be seen in bulging stone walls around the city; as water freezes and expands, it can physically push stones apart. This creates a void in which larger pools of water can accumulate, freeze, expand, etc. Left unchecked, this process called ‘thermal jacking’ can eventually cause structural failure of the wall.
These issues, which are often costly to address, can be avoided or at least minimized through preventative maintenance efforts designed to manage the movement of water.
To this end, we have compiled the following list, that while not exhaustive, identifies some of the typical ‘trouble spots’ that are associated with water ingress, and offers ways to minimize this occurrence.
Roofing: This is really the first line of defense against water infiltration, not just to the interior of the building, but also into its solid masonry walls. Examine, or have a roofing contractor examine the condition of the roof, looking for curled or deteriorated shingles, or shingles that are missing altogether.
Chimney: This is one of the most common areas requiring repair or rebuild. Sometimes this is natural weathering based on the high level of exposure that a chimney faces, but often the lack of a proper cap designed to shed water away from the chimney causes accelerated decay, and allows water to enter the structure from above. Examining the brick or stone below a chimney in the upper regions of a gabled end for example, will often reveal past repairs, a sure sign that water has entered the wall through the chimney in the past.
Flashing: Missing or incorrectly installed flashing not only allows water to gain entry, but can even act as a trough, collecting water and directing it into the building. Ensure that metal flashing is installed and functioning properly in areas where the flow of water is interrupted. These include at the base of chimneys, in valleys and around the top of dormers.
Eavestroughs and Downspouts: These items work in conjunction with one another, and offer one of the most effective ways of managing rainwater and snowmelt. The majority of the water that hits the roof is collected and directed a safe distance away from the building. In the absence of gutters, this large volume of water can run down the fascia, along the underside of the soffet and be deposited against the masonry surface. It may also pool at ground level, and saturate the foundation walls, potentially causing a moisture problem in the basement.
Windows and doors: The junction between window and door frames and surrounding masonry should be sealed using caulking to prevent water ingress. This is an area which if not kept in good repair can allow significant amounts of wind driven rain to enter the wall. Stone window sils should be checked for cracks, and wooden sils should be examined for rot. The condition of mortar joints and caulking around the sil should be assessed as well. Sections of masonry underneath windows and doors frequently require rebuilding, evidence that prolonged infiltration of water has had a detrimental effect.
*A note on caulking: This is a material that can cause irreversible damage to brick and stone, and should be used selectively. Although it creates an effective barrier against water penetration, this same feature can prevent a solid masonry wall from drying out, (an essential function) by trapping water inside. When moisture vapor is not able to evaporate through the mortar joints of a masonry wall, it is forced to travel instead through the masonry units themselves which is an inefficient process and has a twofold effect: The brick or stone becomes much more susceptible to frost damage and more moisture is retained within the wall. This can result in accelerated mortar deterioration, and the breakdown of the masonry unit itself. If there is room, we will typically fill the vertical space between the stone and window frame with mortar, and then because the wood frame and mortar have differential rates of thermal expansion, seal this juncture with a thin bead of caulk.
Mortar joints: Empty or cracked mortar joints are an easy entry point for wind driven rain, or for moisture that accumulates on window sils, and other extruding features. Deteriorated mortar joints should be carefully removed so as not to damage the brick or stone, and the mortar replaced with a lime-based mix suitable for heritage buildings. One of the most common mistakes that homeowners and inexperienced masons make (although well-intentioned) is to undertake these repairs using a cement that does not possess the same qualities of a lime-based mortar, primarily the ability to transfer water vapour described above, and a relatively lower compressive strength which allows slight movements to occur within the building without causing damage to the masonry units. The process of repointing, as well as an overview of lime mortars will be featured in an upcoming article.
Grading: This is another crucial item that is relatively easily addressed, but often overlooked. In this context, grading refers to the contour of the ground around the perimeter of the building. The high point should be against the foundation walls, and fall gradually away from the building, creating a natural form of drainage. When we inspect basement foundations that have historically had moisture issues, we often find low spots around the building that collect and hold water, slowly releasing it against the foundation walls. Although gardens and planters are popular features around the base of buildings, their shape and soil content are not conducive to moving water away, which is something that should be considered when planning gardens.
It is our hope that this article will help draw attention to some of the not so noticeable but extremely important features of a heritage building. The list was compiled based on experience working on a variety of heritage buildings, on projects ranging from residential to commercial and public. Although no two historic buildings are exactly alike in terms of design and environmental exposure, water is a consistent threat, and managing the items on this list will help to minimize its detrimental effects.
For an inspection checklist tailored to heritage buildings, please visit: http://www.gov.mb.ca/chc/hrb/pdf/maintenace_for_heritage_bldgs.pdf