Q: Our company does commercial work that often requires us to construct bollards, which are simply 4- or 6-inch-diameter steel pipes filled with concrete. Concrete is rounded at the top so water will run off. The problem is that our workers don't produce a very uniform product. On some bollards the protruding concrete looks like a scoop of ice cream on a cone, and on others the concrete is nearly flat. I know that the bollards' main function is preventing cars from running into storefronts, but the nonuniform appearance is unsightly.Are there any standards for the proper height to mound the concrete? And is there a device that can be used to give the bollards a uniform appearance?
A: We checked the most recent edition of The American Institute of Architects' Architectural Graphic Standards, and found no mention of a standard height for the curved top of a pipe bollard. We also checked with several finishers, who said they usually just mound up a 4- to 5-inch-slump concrete at the top of the steel pipe and finish it with a small pool trowel. One suggested getting a metal bowl of the required diameter and welding trowel handles on opposite sides, so the concrete could be consolidated and formed by twisting the bowl. If any readers know of a way to produce uniform-looking concrete-filled pipe bollards, please tell us about it.
I've found that mounding concrete about 2 or 3 inches above the steel pipe will result in a good-looking finished product. That's because troweling the concrete compacts it. After shaping the concrete with the trowel and letting it set enough to finish, take a piece of plastic film and use it to buff the top and sides of the concrete as if you were shining your shoes. This will fill in any imperfections and leave a nice surface texture. If you like, you can then pass a finishing brush over the surface.
- Raymond Furtivo, Pittsburgh
Years ago, I was shown an easy method for putting a uniform top on a concrete bollard. Wearing rubber gloves, mold the top with your hands to the desired shape or height. Next, take a piece of plastic film 16 to 24 inches long and 2 to 4 inches wide (a piece of 6-mil polyethylene works very nicely) and, with one end in each hand, place the film over the fresh concrete and gently work it back and forth and around the top to shape and finish. As with any finishing operation, you need to get the feel of it and adjust your motions and speed to fit conditions. To get a really nice finish, go over the bollard top several times as the concrete sets. The more passes, the finer the finish. The only time I have trouble with this method is when using a concrete mix with large aggregate. You need to make sure you have some fines over the rock when you do the initial shaping.
-Ron Mischnick, Walter Mischnick Contractors & Builders Inc., Alliance, Neb.
We get very good results finishing the tops of concrete bollards. We use a 2- to 3-inch-slump concrete and mound it 6 inches. We then rough-shape the concrete with a magnesium float and finish it with a sheet of 4- or 6-mil plastic. We slide the plastic over the concrete surface in alternating directions.
-Herbert W. Katt, president, Katt Construction, Racine, Wis.
To finish concrete bollards, we take a hollow rubber ball, such as a tennis ball, and cut it in half. Next, we twist the half-ball over the concrete in a circular motion to provide a uniform finish. We've built hundreds of bollards using this method.
- William Wells, Bulls Gap, Tenn.
Go to the toy store and buy a fairly stiff hollow rubber ball slightly larger than the bollard. Cut in half, the ball makes the perfect tool for shaping the bollard top.
-Scott Engler, W.G. Clark Construction Co., Seattle