Fleas on cement present a unique problem in that the cement is not a good surface to spray liquid products. The cement will readily absorb most of the spray so there won't be much left behind as explained in our Flea Control article. And keeping the pet removed from the area will only allow the problem to continue as explained in our article as well.

To get rid of the fleas, you'll need to do a few things. First, you need to clean out the garage with a vacuum as well as possible. Since there shouldn't be anything "holding" onto flea pupae and adults (since the flooring is cement) vacuuming should help to remove a lot of the fleas that are developing there right now. This will have a big positive impact. But vacuuming alone won't solve the problem.

Next you need to place out some Drione Dust on the floor. This desiccant dust will dehydrate the flea eggs and other stages and effectively break the cycle.

Lastly, place out some Flea Traps to help collect any that might be able to avoid the treated areas. Following the treatment, someone needs to go into the garage and walk about in there daily, at least once a day, to get the pupae to hatch out. After 1-2 weeks, you shouldn't be seeing any more fleas and at that point you can vacuum again to remove the dust and go back to using the garage like you have been. In the future, apply the Drione every 6 months and should be able to prevent getting another flea infestation out there.