An early start on concrete curing can provide many benefits, especially for hot-weather placements. It can help to prevent stickiness, sponginess and surface crusting conditions that can cause finishing problems. It can also eliminate plastic shrinkage cracking and reduce drying shrinkage cracking. In hot weather, many contractors cure concrete between bull floating and power floating. For large concrete pours, curing may also be needed between screeding and bull floating and between floating and troweling passes.
The three early-curing techniques contractors have used successfully include coverings, fog sprays and evaporation retarders. Coverings work well on smaller slabs, where workers can cover the slab without walking on the surface. The best covering materials are nonstaining wet burlap, polyethylene sheeting and building paper. Fog spraying works well on larger slabs, but the spray nozzles must be positioned around the concrete to ensure complete, even coverage. Evaporation retardants can be sprayed on the fresh concrete surface one or more times during the pour to reduce the moisture-evaporation rate. These chemical compounds work by forming a monomolecular film over the bleedwater at the surface.