Filling joint cracks in concrete
I have a garage with a concrete floor where I do a lot of woodworking. The floor has large scored joints that fill up when I try to sweep up the sawdust. Is there some product that can be used to fill the joint and yet remain flexible enough to tolerate the movement that occurs in the scored joint?
Andy Kelemen, Superior, CO
Rocky R. Geans, a concrete contractor in Mishawaka, Indiana, replies: You have a common problem that is easily solved. First vacuum and then scrub the joint thoroughly with detergent and a stiff brush.
Allow the joint to dry, and then do a water-drop test. The test consists of applying a few drops of water at different places along the edges of the crack or joint and watching to see if the droplets soak into the concrete. If they don’t, continue cleaning until the concrete allows absorption.
Next, install a backer rod (usually polystyrene or foam). Ideally, the backer rod should be installed to allow about 1/2 in. between the top of the rod and the top surface of the concrete floor.
Finally, pour or squeeze joint sealant into the crack or joint on top of the backer rod. (I’ve had good luck with Sonneborn’s SL-1 Joint Sealant; 800-433-9517). Make sure you follow the manufacturer’s directions for drying time. The joint sealant will remain flexible and will keep the joint from becoming a sawdust trap.
One word of warning: Joint sealant is a self-leveling material, so be sure that the joint is packed tight with backer rod and that there are no open areas at the end of the joint where the sealant can leak out. This stuff will find every little crack, void or hole and leak out until the void is filled or you run out of sealant.