About Concrete |
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Dusting Concrete Surfaces |
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Dusting is the formation of powder or chalk at the surface of a concrete slab, usually on floors. It powders under any kind of traffic and it can be easily scratched with a nail or even by sweeping. Common Causes A concrete floor dusts under traffic because the wearing surface is weak. There are at least five identifiable causes of dusting: • Carbon dioxide from open unvented heaters, gasoline engines, ready mix trucks, etc. • Premature floating and/or troweling especially when condensation from warm humid air forms on cold concrete. • Inadequate or improper curing. • Excess amounts of clay or silt in the concrete. • Inadequate protection of freshly placed concrete from rain, snow or drying winds. Prevention • Use low-slump concrete (4-inch max.) • Do not perform any finishing operations with bleed water present on the surface. • Avoid placement directly on poly or non-absorptive sub-grades. • Use proper curing methods to retain moisture in concrete for the first 3-7 days. • Use vented heaters. • Open building for ventilation during production. Repairs 1. Sandblast, shotblast or use a high pressure washer to remove the surface layer. 2. Apply a commercially available chemical floor hardener, such as sodium silicate, metallic zinc, or magnesium fluosilicate to thoroughly dried concrete. If some dusting persists, coat with latex, epoxy sealers or cement paint. |
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