Traditional Masonry Archives — Managing Moisture

Managing Moisture

Lynda Waggoner knows a little something about too much water. She’s executive director of Fallingwater, the famous Frank Lloyd Wright house that cantilevers out over Bear Run in southwestern Pennsylvania. At this house, water is integral to the architectural design, but also a challenge. Flat roofs, terraces acting as roofs, uneven masonry walls that trap rain and snow: All of these characteristics are possible sources of water problems. “We have so many problems with water, but we don’t always know where the water is coming from,” Waggoner says. “When there’s a leak, it may occur on sunny days, rainy days or it could travel — the source could be pretty far away from where the water is seen.”

John Leeke, preservation consultant and owner of Historic HomeWorks Co., of Portland, Maine, knows where Waggoner is coming from. Moisture is the primary cause of deterioration in all kinds of buildings, he says, but it can be difficult to track down.

Many experts liken the process to a crime scene investigation. Leeke, for example, maps out evidence of moisture damage: cracking, deteriorating mortar, efflorescence and the like. “By mapping out the damage, it forces my mind to be objective and recognize the pattern of damage to get to the root cause,” he explains.

Sometimes there are several sources working in combination to cause problems. And there are many kinds of problems.

Historic brickwork consultant Dr. Gerard Lynch reports moisture in brickwork can cause gradual failure of low-fired brick, surface efflorescence and staining, soluble salt problems, decay and washing out of mortar joints, moisture transfer to built-in timbers (leading to dry and wet rot), and corrosion of built-in iron members. Moisture problems can infiltrate a building, moving from one material to another. Plus, moisture encourages frost action and biological growth.

Part of the problem, observes architectural materials conservator John Lee, is that water is not generally well understood. “What is alarming is that there are professionals in the field that lack understanding of water, how it behaves and how it moves through porous building materials.

“There are physical and chemical principles at work. If you understand what’s at work, you can possibly predict the causes,” Lee explains.

Sometimes the cause might go against conventional wisdom. William Rose, research architect with the Building Research Council at the University of Illinois at Urbana-Champaign, tells of The National Memorial Arch, a triumphal arch at Valley Forge National Historical Park, where lots of efflorescence appeared at the mortar joints. Instead of being the result of rising damp, as many believed, the problem turned out to be a roof problem.

“All things being equal,” Rose says, “water will move from large pores to small pores, not from small pores to large pores.” If you see water moving from small to large pores, he says, you will know there is an additional problem, such as a hydraulic head pushing the moisture out.

Most of us learn that water can be solid, liquid or vapor. However, what most of us overlook, Rose says, is bound water — moisture attached to other materials, like the moisture content of wood. Moisture bound inside materials can become a problem when there are changes in temperature. “For porous, hygroscopic materials, cold means wet and warm means dry,” Rose explains. In cool temperatures, moisture will attach itself to the surface, while heat causes moisture to vaporize (in much the same way as a clothes dryer releases moisture from wet clothes), lessening the likelihood of it attaching to the surface.

We also often forget about the moisture we, as humans, contribute to the environment, Lee points out. “Moisture generated by people is basically invisible, but a source of water nonetheless. Water vapor I expire goes over to the wall and can migrate outside. But thermal gradients in the wall might cause that vapor to turn to liquid, which could easily be misinterpreted as a leak in the building envelope.”

Installation of heating and humidification units can cause moisture problems in old buildings that were not designed for them, says Sharon Park, chief of technical preservation services for the National Park Service. “It’s a powerful force, water. If you have too much moisture, it’s a problem, but you can’t eliminate it.”

An important aspect to consider, Park says, is how a building was built and how it was intended to handle moisture. She observes that moisture problems frequently arise because a building was not maintained correctly or because the environment was changed in a way the building can’t handle. Buildings are designed to handle some amount of moisture, but if you change the balance you can get some structural failure, she explains.

Leeke agrees you can’t always remove the cause of moisture, but, he emphasizes, you may be able to develop a strategy to alter its effects. And, Lee adds, you might be able to provide another avenue for its escape.

Sometimes it comes down to basic water management. Take rain, for instance. If rainwater is the problem, the fix may be as simple as repairing gutters or adding gutter extensions. Or it may require grading work or the installation of footing drains.

Rising damp in masonry walls? You may want to install a damp-proof course or, alternately, an evaporative band.

Most experts agree that simply repairing the symptoms of moisture damage won’t solve the problem. Neither will making repairs with improper materials. As architectural conservator Richard Byrne explains, “Basically, improper repairs and mitigation techniques may make the problem worse, or shift the problem, not correct it.”

Park gives an example of buildings designed for a wet environment — such as mill buildings or milk barns — that may have lost the protective parging over their fieldstone foundation. If the parging isn’t replaced with a compatible sacrificial coating, deterioration can continue or get worse.
The use of sealant and waterproof coatings, Lee reports, can alter the permeability of older masonry. “Water will still migrate in the wall, but the evaporation rate will be decreased, so more moisture will move upwards, towards drier surfaces, such as plaster walls.”

Leeke echoes the sentiment that modern construction solutions don’t necessarily work for older masonry systems. “As a standard treatment, someone might repoint a wall. But using hard mortar can prevent moisture movement as it was intended, leading to moisture traveling through the brick and causing deterioration, when, instead, a porous mortar or one designed to fail is what was needed.”

Lynch agrees. “I always use the phrase in my lectures and writings that ‘The joints are the conduit through which the wall breathes.’ It is normally the softer of the two elements — brick/stone and mortar. So the answer is always to repoint in a compatible lime-based mortar which is soft, porous and permeable.”

And that might be part of the problem: trying to align incompatible old and new building technology beliefs. As Leeke observes, in traditional building technology it was understood that all buildings would leak, and therefore, traditional building technology allowed for leaking. Today we believe that, with modern technology, we can build perfect buildings that don’t leak. Unfortunately, they do leak, and it becomes a problem because modern buildings are not designed for moisture.

Lee says he can’t emphasize enough the importance of thinking through the problem before action is taken. “The preservation field is very driven by products, products that may not do what they claim and may not be reversible, or are very difficult to reverse,” he says. For example, a modern product as apparently innocuous as caulk can result in all kinds of moisture damage in older buildings that are supposed to breathe.

Park recommends implementing mitigation solutions incrementally — one at a time, if possible — so you can determine what solutions actually work. “If you do everything at once, you don’t know what’s working or not working.”

However, a word of caution remains from Byrne, who suggests that sometimes moisture movement needs to remain un­impeded. For example, installing a sidewalk next to a building can inhibit the evaporation process adjacent to the building, forcing moisture upwards in the walls.

And then there is one 1830-ish brick house that Byrne recalls had a stream percolating near the back door. When a field across the street was paved over with asphalt, the stream dried up, as did the clay soil surrounding the house. When the clay shrunk, the walls cracked and the building collapsed.

TM