We can clean grout with cracks in it but we would notify you before cleaning it that we are not responsible if there is any damage caused due to these cracks. We would hope nothing happens, but we are shooting water out at 900 lbs of pressure which does have the potential to break up those grout lines. Unfortunately without that pressure you won’t see any cleaning results. Also in saying that we will loosen the seal on our machine so we can have the least suction possible to try to prevent pulled tile slabs. If you have any questions please feel free to give us a call 877-9055.