Q: I try to do things right, and I've never had a dusting floor before, but now I do. What caused it?
A: Check the following possibilities taken from ACI 302.1R-80, "Guide for Concrete Floor and Slab Construction":
- an overly wet mix
- floating or troweling bleed water into the surface
- clay, dirt or organic materials in the aggregate
- water applied to the surface during the finishing process
- using unvented heaters to protect new concrete from cold weather
- inadequate curing, especially if the weather was dry