Expansion Joints and Their Role in Waterproofing

Keeping water where it belongs
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Sponsored by Inpro
Presented By Peter J. Arsenault, FAIA, NCARB, LEED AP
This test is no longer available for credit

Proper Installation of Water-Resistant Expansion Joints

Most expansion joints are installed in concrete that needs to be detailed to receive the particular expansion joint system selected. In the field, this means a quality, properly working, and properly water-sealed joint starts and ends with the concrete block-out formed to receive it. The term block-out simply refers to the recess in the concrete floor structure or constructed wall system that is formed by the general contractor or concrete subcontractor. (Alternative regional terminology might refer to a block-out as rebate, knockout, or cutout.) Block-outs are created so there is smooth transition across the joint to allow alignment of adjacent finished surfaces. Once ready, the expansion joint system is installed by a specialty subcontractor qualified to take on the work.

Concrete Work

A few points are important about the concrete work itself to be sure the expansion joint will work properly. The first is accuracy of the concrete since dimensional variability in the pour can lead to difficulties in installing the expansion joint framing and any waterproofing. In addition, cold joints (i.e., regular gaps that occur with the sequential pouring of concrete) should be avoided since gaps means leaks when water is introduced. The other point to remember is that concrete is porous and not waterproof all by itself so water may come through it simply by capillary action. Add in micro-cracks, honeycombing, spalling, form marks, and voids that can occur when concrete is poured and finished, and there are plenty of other ways that water can find its way through concrete. All of this is significant because expansion joints can account for up to 70 percent of contractor callbacks or claims when dealing with this scope of work. In a vast majority of cases, when a contractor says, “The joint is leaking,” failures or anomalies in the block-out or vertical substrates are the usual culprits, not the joint system itself. Therefore it is important to review the concrete details and installation around the expansion joint to be sure that water-penetration issues have been properly addressed there first.

A critical element of the overall success of an expansion joint system has to do with the concrete block-out that is formed to receive the joint system.

Tying in With Other Trades

We have already noted that expansion joints do not exist by themselves, but rather they must be tied in to adjacent building construction. In addition to concrete, this construction can include wood framing or blocking, steel decking, steel studs and joists, exterior finish systems, masonry, and/or glazing. The challenge with these other tie-ins, and a potential failure point, is the reliance on the skilled craftsmen and women to tie their particular installation into adjacent materials and systems well. For instance, if the glazing specification and bid documents allow the glazing contractor to simply install the frame and glass and does not demand that they tie in to, say, an adjacent waterproof vertical expansion joint, it invites problems. The same issue goes the other way too. If a waterproofing contractor installs the expansion joint system and does not tie in to the window glazing, then it is left unaddressed. In this regard, how the scope of work is contracted and managed by the general contractor or construction manager can be critical to having a watertight installation.

While vertical tie-ins with other systems are important, nowhere is this process more important than in roofs. For obvious reasons, these large horizontal areas are going to require the most protection from water (i.e., rain and snow) so any expansion joint systems that cross it need to be coordinated with the waterproofing.

Waterproof roofing membranes come in two fundamental forms: 1) fluid-applied waterproofing assemblies such as hot mopped asphalt, torched felt/asphaltic layers, petroleum-based built-up systems/SBS, or modified bitumen (MB) asphaltic with SBS modifiers; and 2) thermoplastic single-ply membranes, such as EPDM, TPO, or PVC. Given the range of choices and the fact that some materials interact with roofing materials, one of the most critical questions specifiers must ask is whether or not the counterflashing on the expansion joint system is compatible with the deck membrane and adhesives being applied for the roof. If it is not, materials or bonds could be compromised, causing water penetration and damage.

Based on the above, the tie-in of roofing systems with expansion joint membranes is essential to good waterproofing. One failure point can be the reaction and subsequent degradation when roofing materials and adhesives fail to bond with the expansion joint membrane. This is why it is important for the joint membranes to be chemically compatible with the roofing materials. Good detailing by the manufacturer should clearly lay out the recommendations regarding roofing membranes and adhesives that are compatible with the expansion joint counterflashing.

It is clear that the construction documents need to address these points, but diligence during construction is needed too. Sometimes the specified roofing membrane will be substituted or value engineered for another one when construction starts. This fact may or may not get communicated to the manufacturer of the expansion joint systems. Therefore, manufacturers cannot be held liable if the installer and GC/CM do not coordinate material changes, and clear them with the project architect.

Specification Tips

Many architectural offices rely on standard specifications, including CSI/Master Format Section 079500, which covers expansion joints. If these standard specs have not been updated recently, they need to be because vast improvements have occurred in the industry in just the past two years. As we have seen in this course, there are many new and varied product choices with different applications where they excel.

When specifying expansion joints, particularly when there is a need to keep them watertight, there are some ways to help assure general quality of the products and a proper installation. One of the first points to be sure of is that any specified products have been independently tested and can demonstrate passing results for any or all of the following:

  • ASTM E283-04: This is a test method for air leakage with pressure differentials through a product specimen.
  • ASTM E330-14: This measures how product deflection affects its seal to surrounding substrate.
  • ASTM E331-00: This is a test method for water penetration under air pressure difference. It creates a severe vacuum and attempts to draw water/moisture through the specimen and its perimeter to the substrate. The best can reach hurricane levels without failure.
  • ASTM 1361-11: This measures thermal performance through a product specimen to determine thermal U-factors (convertible to R-values). This is appropriate to show energy-code compliance and minimize heat transfer between building interiors and exteriors.
  • ASTM E90-09: This measures airborne sound transmission loss in building partitions. It is important if minimization of sound transfer through expansion joints is needed.

To determine whether expansion joint products meet any of these standards, or just to determine the best choice of products in general, it is always a good idea to communicate with manufacturers. A quality manufacturer typically provides consultation and technical services for both design and construction professionals alike. The best ones strive be industry thought leaders through the generation of white papers, technical bulletins, and informational videos on hot topics, new product developments, and trends. They can also provide rigorous technical product data and installation instructions to protect the specifier as well as to educate the installer.

To be sure that the installation goes smoothly, specifications should indicate the importance of coordinating with other trades. Per CSI/Master Format, these can include:

  • 033000: Cast-in-Place Concrete
  • 036000: Grouting
  • 040000: Masonry
  • 070000: Thermal and Moisture Protection (Roofing, Above- and Below-Grade Waterproofing, Weather Barriers)
  • 092000: Plaster and Gypsum Board
  • 093000: Tiling
  • 096000: Flooring
  • 097000: Wall Finishes

Finally, be sure to incorporate clauses requiring inspection under expansion joint covers prior to or after cover plate installation. Waterproofing seams, fire-barrier mounting, and cover plate frame inspections should occur for all of these products.


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Originally published in Architectural Record
Originally published in July 2020