white powdery substance on garage floor?

It's called Effllorescence.
It's caused by waterborne salts passing through the masonry.
It happens in new builds when the cement was allowed to get wet, but it usually dries out after a few weeks or months dependent on climate.
If it's continuous it means there is water seepage through the floor from groundwater.
Was a waterproof damp course installed before laying the concrete?

Big Softy
June 2010