Striking off concrete by hand and bull floating

Concrete Construction, Feb, 2003 by Joe Nasvik

The most basic hand tools needed for placing and initial finishing operations on concrete flatwork are a strike-off board and a bull float. Timing is essential during this phase of concrete work. Being organized and ready makes the difference between placing concrete with relative ease or by the hardest physical work imaginable! And in some cases, poor timing leads to removal and replacement. Different types of strike boards and bull floats are available. Here are the essentials.

Strike boards

The old standby is a wooden 2x4, which must be straight and have smooth surfaces. Some finishers paint or seal them to keep water out. But my favorite is an aluminum strike board because it's light, has sharp edges (for more accurate striking), and doesn't absorb water.

Creating a flat, smooth surface is a skill that some finishers develop quickly, while others never do. Performing good strike-off work is the "high art" of placing concrete. Good strike-off people learn to visualize how the board will move. Skill is further achieved by "wet screeding"--establishing finished elevation marks on plastic concrete and striking off to those marks without riding the strike board on a side form or screed rail.

During the strike-off process, the leading edge of the board should be just above the finished plane of the concrete. This will allow a little concrete to flow under the board to compensate for concrete pulled by the board below the strike-off plane. Several passes with the board, moving a little concrete each time, are better than one pass which moves a lot of material. Pulling a lot of material causes concrete below the finished plane to be moved, too, and the elevation will be too low afterward.

When the strike-off operation is performed well, the surface plane of the concrete is flat with few ups and downs to be corrected with a bull float.

Using a bull float

The purpose of bull floating is to smooth the surface of the concrete and make it flat. Small ups and downs that occur during the strike-off process can be removed with a bull float. It also slightly pushes down large aggregate, setting the stage for a better finish to follow.

Bull floats come in several sizes and shapes and are made from magnesium or aluminum. The ends of the float can be rectangular or circular. They are set up with attachments connecting to extension handles (which either screw together or snap together) that will change the angle of the bull float to the concrete surface. This happens by twisting the extension handle or by moving the extension handles up and down. I prefer a 45-inch long bull float with rectangular ends. It's best to perform this operation immediately behind the striking-off process while the concrete is still plastic.

When bull floating, keep a low angle to the concrete. If you don't, you will plow concrete, pushing it ahead of the float--ruining a good strike-off job! It's also best to stop the bull float about 1 foot from a form line to avoid pushing concrete down at the form. Sometimes when the concrete is too high or too low in small areas, you can "juke" the bull float back and forth quickly, an inch or so at a time, to make the concrete more liquid and cause it to move toward low areas.

After the first pass with the bull float, there will be edge marks on the surface of the concrete. A second pass, performed after the concrete has stiffened somewhat, will further flatten the surface and reduce the edge marks. You are now ready for the next finishing step--waiting for initial setting to occur and the bleed water to rise and evaporate--followed by troweling, edging, and jointing.