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In 1984, Kistner Concrete Sales Engineer Clarence Conrad called EJ Facilities Manager Tim McKernan and said, "I've got a problem."
"Kistner was the first precaster that EJ worked with directly when we started manufacturing access hatches," McKernan explains. "And our hatches weren't the problem; Clarence was frustrated by a part of the precasting process that came up every time hatches of any kind were cast into concrete vaults."
Conrad explained that hatches are usually set into concrete structures of greater thickness than the hatch—for example, a hatch with a total thickness of 3.5" would be set into an 8" thick concrete slab. To keep hatches flush with the final surface and to keep openings clear, precasters had to build solid forms to support the hatch during pours. In the above example, a 4.5" frame would have to be built to match the hatch dimensions, and it had to be sturdy enough to stay in place during the concrete pour. This worked, but it created several problems:
After listening to Conrad's explanation, and reviewing the precasting process, McKernan proposed an elegant solution- access hatches would be extended by lightweight aluminum "skirts", so that their total thickness would match that of the proposed slab. This proved to be a winning solution with several advantages over the old process:
Now this simple, innovative idea has become a precast industry standard. "Really they work for anyone, even contractors working on site," McKernan says. "But precasters tend to value it more than others, so this is mainly for them." Conrad agrees; "The skirts are efficient, cost-effective, and make for a higher quality product—they're a great innovation."
Many manufacturers now provide similar forming skirts, but McKernan likes to point out that EJ still makes a better product; "Everyone has copied this, but we invented it. And most of the copiers have just a few limited heights—we're more flexible and can do anything, so custom thicknesses for particular vaults or structures are not a problem."
"The skirts are efficient, cost-effective, and make for a higher quality product—they're a great innovation."
Clarence Conrad, Sales Engineer at Kistner Concrete
More recently, EJ has extended the forming skirt idea to their line of ductile iron hatches with a modified version of the skirt that can be set in place within a slab form. The heavy iron hatches are then set securely in the skirt, which supports them during a pour without the need for suspension by a crane or gantry. It's another way EJ speeds up precasting and lowers costs for manufacturers.
"We weren't thinking about patents back then," McKernan says. "But that little idea really caught on, and I'm glad. It's made life easier for an important infrastructure industry."