January 1, 2013

Appalling spalling

Incorrect landscaping technique continues to damage homes

A landscape designer takes a look at solutions to problems created by laying pavers over steps or against a brick wall.


While driving around Ottawa earlier this year, during the course of my regular work-day, I noticed an inordinate number of brick homes with ugly water stains and excessive efflorescence. It was obvious these were caused by weep holes being partially or completely covered by pavers or garden walls. It seemed like everywhere I looked there were examples of landscaping projects causing efflorescence. I was struck by how many homes were affected in such a small area, and couldn’t help but think how many more homes across the city, and the country, are similarly affected.

The problem was so striking and pervasive that I decided to do something about it. In two 30-minute sessions, in two completely separate areas of the city, I photographed countless examples of landscaping projects causing efflorescence. I sent this information to several suppliers, as well as engineers at the Interlocking Concrete Pavement Institute (ICPI), and Tony DiGiovanni at Landscape Ontario. I believed the problem was widespread enough that I needed to get industry leaders involved. The response was quick and decisive. A task force was created to look into the issue. It was made up of members of the ICPI construction committee, engineers from a few landscape masonry suppliers, and key members of Landscape Ontario. It is hoped recommendations from this task group will be available for the 2013 season.

Why is this happening and why is it such a big deal? Efflorescence in itself can be benign. As most anyone in the industry knows, efflorescence often occurs in the natural curing process of concrete products. When moisture in concrete products evaporates, it can often leave behind salts that are not bound to the cement. This manifests as a white powder that can simply be brushed off. Persistent efflorescence occurring from trapped moisture is another issue altogether and is usually indicative of a more serious problem — one that could cause bricks to spall.

What is brick spalling and what causes it? Brick veneer is a very porous material and acts almost like a sponge. Weep holes allow water buildup from wind-driven rain to escape. Weep holes also allow for ventilating air to circulate behind a wall to help dry the building’s structure. When weep holes are covered, even partially, moisture can get trapped in the brick. Water expands when frozen. When moisture-laden bricks are exposed to freeze/thaw cycles, the water expanding in the brick will cause the face of the brick to eventually shatter and flake off or spall.

While brick spalling as such should cause worry, it could be symptomatic of concealed damage that can be of even greater concern. If moisture buildup goes unchecked, it could lead to serious damage to wall and floor structures. Over time, rot can set in and eventually invite insect damage. Quite often this more serious destruction doesn’t become evident until considerable damage has been done.

Why is this happening and what can be done about it? Going over the photos I took, I noticed three specific areas of concern.

Garden walls built at or above the brick veneer line
This problem is probably the easiest to deal with, and almost falls into the common sense category. I noticed a lot of homes with raised garden beds built at or above the brick line. It’s a given that garden walls built above a house’s brick line and filled with soil will block the weep holes and cause problems, but even walls built at or slightly below the brick line can cause a problem.

In the Landscape Guide for Canadian Homes, published by the Canada Mortgage and Housing Corporation, the recommendation is to keep the ground surface at the house 15cm (6 in.) below the lowest course of bricks or 20cm (8 in.) below stucco or siding. Ground splash back from heavy rains could cause moisture problems in the summer, and snow and ice buildup could cause moisture problems in the winter, if these guidelines aren’t followed.

This is one case that can easily be resolved with a bit of education. A note could easily be added to construction details available in supplier catalogues and ICPI training manuals that reflect the recommendations from CMHC.

Porches covered in thin veneer-overlays
Covered concrete porches or “overlays” is another landscape project that seems to cause efflorescence problems. Several years ago, someone had the idea of covering concrete porches with pavers; if it can be done with flagstone, then why not paver products? This practice became so popular that several suppliers introduced a variety of thin pavers specifically designed to cover concrete porches. While overlays are a great idea and offer homeowners a solution to dull, drab concrete steps and porches, they are often installed improperly or in the wrong conditions.

Some paver manufacturers supply technical guidelines for concrete system overlays, but they are usually cursory, technical cross-sections that aren’t detailed enough for most practical purposes. These construction details usually address proper drainage, away from the house, on the surface of the overlay, and water buildup in the supporting bedding sand. They call for the usual two per cent slope away from the house, and step caps to be glued in lines perpendicular to the grade rather than across, so as not to obstruct drainage. The problem here is they don’t deal with installation against masonry walls. Even when thin pavers are installed as an overlay, there is still the possibility that over time polymeric sand, or even dirt and debris, will block the partially covered weep holes and cause a problem.

It’s clear that the technical information currently available for covering concrete is lacking — especially when it comes to overlays installed adjacent to masonry. In the vacuum of proper guidance, many contractors come up with their own solutions. Some have suggested drilling out weep holes on the next highest row of bricks above the pavers, but that seems to have very limited success. Some suggest sealing the bottom row of masonry and drilling out the next row. Some use a thin slice of dimple board against the brick to provide spacing. The solutions are varied, but even following currently available best practices, these solutions can yield mixed results. A proper solution to overlays against masonry has to come from the industry.

Raised steps and patios against brick masonry
Raised decks and steps, built against brick masonry, is another area of concern I came across. Many contractors today build steps and large raised patios against brick homes using the same methods they would against a siding or stucco home. They apply waterproofing (blue skin or dimple board) and then build their steps or walls directly against the home.

Six or seven years ago I was contacted by a customer who wanted repair work done. A contractor had built a large raised deck almost the full length of the back of the house. The overall project was amazing — a beautiful job on a stately home in a very affluent neighborhood.

Unfortunately the raised deck was built against dimple board only, and all the bricks along the edge of the deck had spalled. Since the repair work was several thousand dollars, I never heard back from that homeowner, but I was struck by how much damage it caused — and that was damage I could see.

Several years ago I contacted ICPI to get recommendations as to how to build against brick. The answer was simply, “Don’t.” At the time, the recommendation from engineers was to build wood or metal stairs down to a patio area when designing against brick houses. But many homeowners choose brick because they love the low maintenance that paver products provide.

Out of necessity we came up with our own way of building against brick homes. We designed our steps to have as small a footprint as possible. We would build a “fake” wall inches away from the house and then mortar or glue the back paver to the fake wall. That kept costs down, gave the homeowner a project with a unified look, and kept what was essentially a free-standing structure away from the house. This let the weep holes do what they were meant to do — allow moisture to escape. The reduced size of the steps meant fewer weep holes were covered. Even though there was a gap between the stairs and the wall, we believed smaller steps would enable more air circulation behind the masonry. 

The ICPI teaches a technique that closely mirrored what we have been doing when building against brick homes. This method called for a stress relief wall (hidden wall) as a way to keep lateral soil pressures away from the structure’s exterior. While this seems to have been developed primarily to deal with lateral forces against all types of walls — to mitigate excessive force blowing out foundations — the specification also acts as a way of keeping weep holes free.

Although I’m not an engineer, I would imagine that as more masonry is covered, more air becomes stagnant. Unless new specifications become available, I think I’ll stick with my rule of designing smaller steps or raised patios over masonry whenever possible.

Education is the answer
In my view, the damage resulting from landscaping projects built against masonry walls can be attributed to unclear industry specifications, poor education and communication, and a lack of research and development. Building garden walls at or above a home’s brick line, for example, is something that could easily be dealt with by improving communication. Something could be added to installation specifications from suppliers, and ICPI could include it in their manuals.

In the case of concrete overlays, I think more information is needed. Even with the currently available best practices, there is probably still the potential for weep holes to be covered. Perhaps something could be installed adjacent to masonry walls, a mini channel drain, if you will, that would push the pavers away from the weep holes and allow them to do what they were designed to do. I’m certain most paver suppliers have R & D centres that could devote a little time and effort to developing a creative and effective solution to keeping weep holes clear.

Finally, in the case of building steps and raised decks against homes, I think ICPI has a very good solution in its specifications for a hidden relief wall. It seems like the perfect answer to keeping weep holes exposed and brick masonry walls properly ventilated and dry. All that is necessary is for this information to make it to suppliers, so they can include it in their available ICPI tech specifications.

One thing is clear. The visible damage that is currently being done to masonry on homes is real and prevalent, and reflects poorly on our industry. It’s going to take a concerted effort by all concerned to deal with these issues. Yes, contractors need to take the initiative to better educate themselves and their staff; but manufacturers have to work with industry associations and engineers to develop clear, effective, practical solutions and best practices where none exists or confusion persists. If solutions aren’t available or a product isn’t right for a certain situation, then communicating that should be just as important — even if it means lost revenue in the short term.

I don’t know where I picked this up, but when things get hurried and stressed I’m often fond of saying, “There is no such thing as a landscaping emergency.” In this case I may well have found one. It may not be a medical emergency, but as landscape professionals, maybe we should borrow from the physicians Hypocratic oath and …first do no harm.
Bert Minor is an Ottawa-based certified landscape designer.