Keeping Expansion Joints Weather Tight

Architectural expansion joints are often necessary, predetermined gaps in structures that are designed to absorb environmental movement in buildings. When done right, they tend to be integrated with their construction such that they blend in with a design and almost disappear. Hence, it is easy to overlook the fact that they can be a potential source of water and moisture infiltration and damage. That infiltration could be problematic for the expansion joint itself, or it could cause problems for other building materials or occupants too. Either way, when using expansion joints that need to cut across exterior surfaces, their ability to resist water needs to be factored in along with the other requirements for the joints.

At the most basic level, expansion joints are a necessary component that must be engineered to handle movement between adjacent structural sections or components. Filling the resulting gap with an appropriate material that can expand and contract along with the building is the essence of expansion joint filler and cover design. The details of both the material used and its connection to the adjacent surfaces are what manufacturers of these systems focus on to assure that successful products and applications are possible. For example, when a joint filler and cover are used for floors, high durability is needed to withstand pedestrian traffic, push carts, scissor lifts, etc. Similarly, when it comes to acting as a moisture barrier, a continuous, sealable connection is needed to prevent water infiltration. This may include a means to help channel rainwater away from the joint and toward predetermined drainage points. Either way, the system needs to prevent water infiltration, which could do damage to the filler and cover system first and then go on to damage other areas of the building.

Water and moisture control are particularly important if the expansion joint is in a fire-rated assembly since the joint filler and cover will need to be fire rated as well. The apparent paradox of providing an intentional break in the structure to allow for normal expansion and contraction while still maintaining a fire rating is addressed by providing an expansion joint fire barrier that is tested for performance. However, since these fire barriers become worthless if they are wet, preventing water from entering a fire barrier is also critical to life safety. In that regard, choosing a supplier for expansion joint systems and fire barriers that are truly effective cannot be overstressed.

With all of the above in mind, there are three common types of barrier expansion joint systems that can be considered. The suitability of each for a particular project condition will depend on the size of the joint or gap as well as the conditions which the joint are subjected to.

Compression systems are typically for 4-inch and smaller expansion gap widths. These products are commonly comprised of mineral wool strips held in place through compression. These are topped with sealant to secure the barrier in place and protect it from water infiltration. For fire rated versions, fire lab testing of compression systems is typically done for both concrete and drywall conditions.

Foam seals are suitable for 6- to 8-inch and smaller gaps and conditions where abuse is not likely. In certain applications, the use of foam seals in expansion joints provides a solid seal against the elements, providing both thermal and moisture protection. Open-cell foams provide some breathability and are best in vertical applications, allowing any moisture that becomes trapped in a wall cavity to wick out. Closed-cell foams are watertight and block water from entering—whether in liquid or vapor form. This is the best application for horizontal runs where water could penetrate and pool where it is not wanted.

These are tougher to compress but do very well when placed under tension (i.e., expand). Closed-cell foam can also be utilized on below-grade vertical applications as support and closure to positive side waterproofing at expansion joints.

A variation on foam seals are those that are impregnated with wax to help keep joints watertight and have been in use for about 50 years. However, some consider the addition of copious amounts of wax as outdated, but that is only true up to a point. Generally, a 2–3 percent wax impregnation is viewed as the best alternative since it drastically increases the hydrophobic properties of the foam and extends the lifespan of the seal. If wax impregnation isn’t selected, then the plain foam can act just like a sponge and soak up water. In addition, plain foam assumes an unrealistic expectation of perfect installation of the silicone face in manufacturing and field perimeter caulk seals to keep the foam protected. If the face silicone seal itself is damaged—say, by the tip of a caulk gun jammed between the foam and wall or deck material—then leaks will occur. With wax impregnation, the foam seal will remain watertight even if the silicone face seal is compromised, primarily because wax doesn’t dry out.

Blanket-style seals are the most versatile system, suitable for expansion joint gaps of 2 through 32 inches and able to withstand high rates of movement. These are often used for maintaining fire seals too and come in two forms: either ceramic cloths with intumescent layering or graphite sheet goods encasing insulating blankets. In seismic conditions, they allow for approximately 50 percent of joint compression and expansion movement. Some models are able to retain their rating throughout lateral shear movement testing, while others cannot.

Blanket seals can be specified either to withstand water or not. Those that cannot withstand water exposure and become wet are often rendered useless against smoke, fire, and heat, and even after redrying carry diminished fire resistance. Products that are rated and tested for water exposure during or after construction or for open structures, such as parking facilities and stadiums, provide fire protection even if they become wet. It is important then to select and specify the appropriate material for the water conditions anticipated in the building. This is especially true when using fire-rated blanket seals since they need to be fully and carefully connected to the adjacent concrete surfaces and form a continuous barrier where vertical and horizontal conditions meet. At least one manufacturer has addressed this concern through the use of a modular system that allows separate sections to nest together, creating tight, continuous protection. Further, the edges of the blanket are preattached to metal flanges instead of relying on field installation to create an uncertain seal. These preattached flanges drastically reduce labor costs and ensure a uniform installation for a more reliably continuous seal.

Having looked at some of the basic parameters and design implications of these various materials and systems, we will now turn our attention to more specific aspects of their performance.

Images courtesy of Inpro

Three common types of expansion joint systems that can resist both water and fire include compression systems with mineral wool (left), waterproof, fire-rated foams (center), and waterproof fire blankets (right).

Crystalline Concrete Foundation Performance

Crystalline technology applied to concrete has been tested by independent bodies to determine its effectiveness not only for waterproofing but also for overall durability, including resistance against chemicals. For example, testing carried out at the University of Wisconsin-Milwaukee was based on field testing of nine concrete bridges that had been treated with various corrosion mitigation strategies, including surface sealers and three different admixtures. At a 2-inch depth, the bridge section treated with crystalline technology showed an average 55 percent reduction in chloride content (road salt) as compared with the control section. This indicated a very strong level of protection against chloride penetrating the concrete and causing damage to reinforcing steel and the concrete itself. Testing has also shown that concrete that has been treated with crystalline technology has an enhanced resistance to chemicals in a wide range of pH levels. Crystalline technology treatment was shown to suppress the erosion of the concrete mortar exposed to sulfuric acid to one-eighth that of untreated specimens.

In addition to these types of crystalline concrete testing, visual evidence of the effect of the crystals can be found using scanning electron microscope (SEM) images. SEM is a technique whereby a precise photographic image of a microstructure is produced by scanning it with a focused beam of electrons. Extremely high degrees of magnification can be attained and, at 500-times magnification, crystalline formations at work can be seen. This visual evidence found by subjecting cores or samples of crystalline concrete to SEM procedures applies not only to small pores and openings, but it also shows that it can actually help “heal” cracks that may occur during concrete curing.

Images courtesy of Xypex Chemical Corporation

Scanning electron microscopes (SEM) were used to capture the images shown here of crystalline technology being successfully used to fill and seal small pores and gaps in concrete (left) and to help “heal” cracks that developed during curing (right).

To get a sense for how crystalline concrete works in actual building projects, consider the experience of Derek Vander Ploeg, president of Vander Ploeg and Associates, an architecture and planning firm in Boca Raton, Florida. He reports that the firm specified crystalline concrete on two large projects in Boca Raton, known as 327 Royal Palm and Tower 155. Both projects were decidedly different in terms of their concrete foundation system. 327 Royal Palm was a hydrostatic slab with deep piles ranging 30 to 35 feet below grade, with a total dynamic head pressure (TDH) of 22. Tower 155 was a matt slab ranging from 42 inches to 6 feet in depth with piles 20 feet below grade and a TDH of 20. Crystalline concrete was used for the concrete foundation walls on both projects and in the slabs.

Vander Ploeg notes that the crystalline technology used made both of the slabs “beautiful” and says, “It seems the finishers had extended working time, thus really improving the finish on 8,000 psi concrete.” A vast quantity of concrete was used in Tower 155 so placement of concrete was significantly enhanced from every perspective using crystalline concrete. Vander Ploeg adds, “With all the cold joints in the slab and the walls due to the mass amount of concrete and many separate pours, there isn’t a leak anywhere. Both projects are dry. The technology is amazing, and it really works well under pressure”.

When asked what made Vander Ploeg decide to use crystalline concrete, he replied it was “due to limitations in construction logistics, such as tight space allocation, thus difficulty installing membranes and the need to accelerate the construction schedule due to the densely populated area. Both were critical elements in deciding to use crystalline concrete. Plus cost savings was also a significant benefit.”

Jim Caruth is the technical services manager of XYPEX Chemical Corporation, a manufacturer of crystalline chemical admixtures. In his experience, he has seen that “crystalline technology is a high-performance waterproofing system that can provide a cost-effective stand-alone waterproofing solution or be used as part of an integrated system in conjunction with other waterproofing materials. Frequently used as a stand-alone waterproofing system in water holding structures and below-grade parking or industrial spaces, it is often specified in addition to other waterproofing systems for added assurance in critical below-grade habitable spaces.” Clearly, it has proven itself as a reliable, breathable, repairable, cost-effective waterproofing system for most concrete structures.