Q.: While a slab was being floated and troweled the wind blew polystyrene beads onto the surface. These came from loose fill insulation in an adjacent concrete block wall.

The finishers could not remove these lightweight particles and the particles got worked into the surface. This marred and pitted the finish. The beads were too numerous to be picked out of the surface by hand. The blemishes promise to be dirt catchers as well as being unsightly. How can these numerous pits be repaired?

A.: If it is possible to accept a floor that is slightly thinner and that has an elevation a fraction of an inch lower, you might plane the surface. Otherwise you might repair by power wire brushing the beads out of the surface, then squeegeeing an epoxy over the surface. Some of the methods specified in ACI 503.3, "Standard Specification for Producing a Skid-Resistant Surface on Concrete by the Use of a Multi-Component Epoxy System" may be useful. This appears in the ACI Journal, September 1978, page 448.

It would be best to refrain from placing any type of loose insulation that could become windborne on the same day that concrete is being placed. It would also be advisable to make sure that previously placed insulating fill is protected from exposure to wind during finishing operations.