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Leaving A Lasting Impression - California Builder & Engineer Magazine (Posted: 2002-07-26)
Allen & Sons Construction Inc., in French Camp, California, have developed the patented SlipStone Extruded Wall system capable of impressing a pattern into all three sides of a slipformed wall.

It's said that necessity is the mother of invention and it's true in Allen's case. They wanted to be competitive in the market and saw that the traditional methods of decorative wall was too labor intensive and took too long to complete.

"This has been in the back of my mind and I said look, I have this beautiful GOMACO machine, we need to find out if we can do this," Michael Allen Sr., president/owner of Allen and Sons, said.Since Allen and Sons is the innovator of this vertical-slipforming concept, they had no one to turn to for roller molds or advice. They built their own.

"We went out and found the rocks we wanted, placed them and made a plaster of paris mold of our rock wall," Allen explained. "We cast another mold to get the reverse and then poured a rubberized material in the mold. We took our mold and wrapped it around an aluminum cylinder, bonded the mold to the cylinder and stood it up on our new generation Commander III."

Mounting the roller to their machine required modifying their mold. "We added on about 2 feet to the back side of our GOMACO mold for a one roller process," Allen said. "We attach it with adjustable arms to control the depth of the impression we're trying to get out."

They tested their new design out in their yard and knew almost instantly their work and ideas had paid off. The SlipStone method of slipforming barrier wall was born.

"I had guys tell me I was crazy for attempting this. That I would never get my wall to stand up," Allen said. "I've proven them wrong."

They put their new method to the test on a project in Modesto, California, slipforming wall around a man-made lake in a new lakefront community. The project involved slipforming approximately 3,600 feet of imprinted wall with their new generation Commander III.

As slipforming progressed, Allen found they were having troubles keeping material buildup off their SlipStone roller. They tried using a form release agent.

"I came back to the yard after a day of placement and said we just had to come up with something better," Allen said. "It was just too expensive and labor intensive to keep the roller clean."

"We went back to the Commander III, put another stud behind the roller, set the roll of plastic tablecloth on it, placed the plastic in front of the roller, and once we started placing, it just imprinted right on the wall."

Allen was able to cut his six-man crew down to only two men behind the machine. After 30 minutes, the crew is able to pull the plastic off the wall.

The wall on this project is 4 feet tall by 12 inches wide. As Allen was slipforming his wall, he heard something most contractors are never told. The projects developer told him his wall was too straight.

"All these years we've been trying to make our wall perfect and then this guy comes up to us and asks us if we can't make if crooked," Allen said. "The wall was actually too straight so we started bumping the stringline every once in a while and we also physically put our mats on the top of the wall and knocked it down a little bit."

They also resorted to a mix design with a higher concrete slump. It averaged 2 inches. Production averaged 600 feet per day. With better working conditions, Allen says he'll be able to slipform approximately 1,000 feet of imprinted wall per day.

The next phase of their SlipStone development will include a tall wall roller. They are working on a roller for a 6-foot imprinted sound wall around a subdivision. They're also working closely with landscape architects at the California Department of Transportation.
For comments and questions regarding this article, please contact:
Kelly Krueger
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