Whether you're a newbie or seasoned veteran, there's a lot that you may be overlooking when it comes to repairing masonry cracks the right way. Michael Schuller, P.E., president of Atkinson-Noland & Associates, Inc., a consulting engineering firm located in Boulder, Colorado and New York City, explains here the difference between cracks in masonry and those in concrete. See him live at the World of Masonry 2015.
Q: What do masonry professionals need to know about repairing cracks?
Schuller: Most people repair cracks in masonry the same way they repair cracks in concrete, which can be very damaging. Using high-strength modern epoxies is fine with concrete, but it just doesn't work well with most masonry, which can have open mortar joints or internal voids that eat up a lot of epoxy. Even worse, using a high strength material to repair historic masonry (which is usually low strength and low stiffness) can be damaging in the long run as loads shift to the repaired zone. So masonry professionals need to learn the proper techniques and materials to repair masonry cracks.
Q: What other critical mistakes are you seeing?
Schuller: People waste a lot of money pumping concrete repair epoxies into voids in masonry walls. It is much better to use compatible cement- or lime-based injection grouts for masonry.
Q: When it comes to masonry cracks, are there any misconceptions?
Schuller: A crack does not necessarily mean the building is failing. An engineer needs to look at it, but usually cracks just mean loads are redistributing or they could simply be caused by temperature and moisture expansion.
Q: Would you say that, in general, masonry professionals need more insight into new materials and methods as opposed to “doing things the way they’ve always been done”?
Schuller: Knowledge is always good. In the masonry industry we need to catch up with other industries, and use new materials or processes that simplify repairs but at the same time do not get us into any problems. Too many people fix cracks without diagnosing the cause of the crack, and then the crack just comes back! We need to treat the cause first, then address symptoms.
Q: What’s the most important thing that masons need to know about crack repair, that perhaps they’re not paying attention to?
Schuller: Repair materials must match the properties of original materials. The concept of repair material compatibility is often overlooked and has caused many repairs to fail. Using the wrong repair materials can lead to stress concentrations or change how moisture vapor passes through walls, hastening deterioration or damage.
Q: What would be your first step in approaching a project repairing cracked masonry?
Schuller: The first step is to map out cracks, using sketches or drawings. This helps in understanding whether there is a pattern to the damage or if it is just random. The shape, orientation, and width of cracks can all help when diagnosing cause.
Q: How would you describe the challenges young masons are facing, in terms of their understanding of managing repairs? What about seasoned veterans?
Schuller: Younger masons may have a hard time making sense of all the products out there and sometimes look for the quick fix. Once they've been around a while they understand what works and what doesn't. Those that have been around a while get set in their ways and may not know of new technology. For example I see a lot of masonry repairs carried out by demolition companies–there are new methods for repairing or strengthening in place.
Q: You mentioned that masons need to “treat the cause first, then address symptoms”. When that means extra time, work, and expense, how do you handle a client who essentially doesn't want to spend the money to do the job right?
Schuller: Well I just don't do the job. Or I get it in writing–the understanding that cracks will reappear (soon) if the cause is not addressed. You cannot go back and repeat repairs under warranty or you will go out of business. That said, sometimes it can makes sense for the client, financially. For example, if foundation underpinning is required (costing tens of thousands of dollars) it may make more sense to spend $1000 every year or two to repair cracks, as long as it doesn't turn into a stability or structural issue.