Q.: Can I safely use a self-propelled, laser-controlled screed to strike off concrete for a post-tensioned floor without damaging the post-tensioning cables?

A.: To answer your question, we contacted Dave Somero, a concrete contractor whose father invented the Laser Screed. He says you can use his company's machine to place concrete for post-tensioned floors, but you must take a few precautions. The subbase beneath the plastic slipsheet should be a sandy material so sharp rocks can't damage the post-tensioning cable sheathing. If a crushed stone material is used for the subbase, be sure to choke it off with fine material before placing the slipsheet. To further prevent damage to the cable sheathing, don't make sharp turns with the Laser Screed, and always keep the screed moving when turns are made.

Chair up the cables to the correct elevation directly in front of the machine, and place the concrete with a boom pump if at all possible. If the concrete is placed from truck chutes, requiring concrete truck tires to roll over the cables, sheathing damage is possible.