What is a screed, and what is its roll in placing concrete?
To remove concrete in excess of that which is required to fill the formevenly or bring the surface to grade, performed with a straight-edged pieceof wood or metal by means of a forward sawing movement or by a poweroperatedtool appropriate for this purpose. The name applied to the toolused to fill the form evenly.
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 Craftsman 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.