Concrete Dusting

Q: I have a concrete driveway about 24 by 60 feet that was poured one year ago. About three weeks after installation, the surface appeared "dusty" and wet leaves made spots on the driveway. What causes this problem and what can be done to correct this?

A: "Dusting" usually occurs occurs on concrete surfaces when the water-to-cement ratio on the surface is too high or bad finishing techniques were used. It could have been a very weak mix of cement, not enough cement on the surface, or too much water.

It's a good idea to have your driveway tested for strength. This test involves drilling a six-inch diameter piece core from the floor (which will then be replaced) and having a concrete laboratory test the strength of the concrete. A properly mixed one-year-old driveway should achieve 2800 psi.

If licensed contractors are required to warrantee their work longer than a year in your state, contact the concrete contractor who originally installed your driveway and ask him to have the floor tested.

If they don't know who to contact, have him or her ask a structural engineer for a referral to a good concrete lab in your area.

If they are unwilling to do so, paying for it yourself will give you the information you need to determine if the driveway should be replaced.

Wet leaves left on a driveway will have a tendency to stain, but can be cleaned up by a professional powerwasher or you can mix hot water mixed with tri sodium phosphate (1 pound per gallon).

Kathy Maynard has been matching homeowners with home improvement contractors since 1990 and has written scores of articles advising homeowners how to find, hire and work with reputable service professionals. She also authors Weekend Warrior, a weekly home improvement column in The Sacramento Bee.

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