We've been in the slabjacking business for about four years and have successfully completed many jobs. However, we sometimes have problems completely filling the void beneath the slab. What are some possible causes?
We spoke to John Meyers of American Concrete Raising Inc. and he offered some possible causes. The holes you are drilling to pump the grout through may be too big. Drilling large diameter holes increases the occurrence of "breakouts" in which concrete fragments break off the underside of the slab and settle in the void. If not detected and removed, these fragments can impede flow of grout to the void. Using a button bit rather than a star bit also helps to prevent breakouts. Meyers also suggests that you begin pumping the grout under low pressure. High pressure removes water from the grout, creating a thicker mix. If you start pumping under high pressure, the mix may clog near the hole and prevent the grout from flowing into the remaining void. Pump the grout under low pressure until you get some resistance. Then gradually increase the pressure until you notice the slab lifting. Slab movement indicates that the void is full.