Friday, January 01, 2021
Sunday, September 16, 2018
To understand what a waterstop is, it is helpful to understand what it is not. Waterstop will not prevent the migration of moisture through a concrete slab, protecting the installed flooring system (such as tile or hardwood) from adhesion failure or deterioration. Nor will waterstop have any effect on capillary water migration through concrete walls. Vapor barriers, drain boards, concrete admixtures, bituminous wraps, flashings, and multiple other construction products are available to the specifier, contractor, or end-user for these criteria and there are many good books written on the subject.
Waterstop has a singular purpose: To prevent the passage of fluids across and along concrete joints. Waterstop does all of its work at the joint. Because concrete joints are frequently open and subject to hydrostatic loads, a strong case states that waterstop has the most critical role in fluid-proofing a concrete structure. A pinhole or imperfection in a vapor barrier will have little to no noticeable effect, but even the slightest defect in a waterstop product or its installation can be truly catastrophic to the fluid-tight integrity of the building envelope.
The first waterstops used in construction were strips of lead or copper. In the early 1900s, the preferred waterstop material shifted to vulcanized rubbers such as neoprene or styrene butadiene rubber (SBR). While rubber waterstops had excellent mechanical properties (high tensile strength and elongation) they had one major weakness: they were challenging to fabricate as the rubber was vulcanized, meaning it had already taken a “set” (thermoset) and could not be heat welded together like the metals used previously.
In 1926, Waldo Semon of the B. F. Goodrich Company invented plasticized PVC. Semon was attempting to dehydrohalogenate (non-plasticized) PVC in a solution of boiling solvent to create an unsaturated polymer that would be useful for bonding rubber to metal. The results of Semon’s experiment was the creation of a thermoplastic with properties very similar to rubber.
It took many years for plasticized PVC to find suitable commercial applications, and was first used as a waterstop material in the early 1950s. Back then, the material was properly labeled as fPVC or flexible PVC. The first wide-scale test of any waterstop was performed in 1954 by the Hydro-Electric Power Commission of Ontario, Canada. Many manufacturers still use the results of this test as a benchmark, and other than some new polymers, waterstop has not changed that much since then.
Tuesday, December 16, 2008
I've always been somewhat surprised by the Corps of Engineers continued use of PVC dumbbell waterstop in their flood control and dam projects. After Hurricane Katrina hit, and large portions of floodwall needed to be repaired or replaced, the COE's design still called out for this largely out-dated style of waterstop. Dumbbell waterstop functions like a cork in a bottle, with the large end bulbs simultaneously acting as both anchors and internal dams. Historically, dumbbell waterstop is one of the leakiest varieties of waterstop, as the large end bulbs when pulled under tension distort to an elliptical shape, while the concrete cast against them remains in a round shape and therefore creates an annular void for water to migrate through.
Now, large portions of the rebuilt floodwall in Kenner, LA are leaking and expensive repair procedures are taking place. I would imagine that simply by specifying a ribbed centerbulb waterstop this entire failure could have been avoided.