Dusting Concrete

Formation of loose powder resulting from disintegration of surface of hardened concrete is called dusting or chalking. A concrete floor dusts under traffic because the wearing surface is weak. This weakness can be caused by:

• Any finishing operation performed while bleed water is on the surface or before the concrete has finished bleeding
• Poor finishing practices such as broadcasting dry cement to speed up finishing or sprinkling water to the surface while finishing
• Floating and/or troweling operations following the condensation of moisture from warm humid air on cold concrete
• Inadequate ventilation in enclosed spaces
• Insufficient curing
• Inadequate protection of freshly placed concrete from rain, snow or drying winds

Dusting can be repaired in the following ways:

• Sandblast, shot blast or use a high-pressure washer to remove the weak surface layer
• To minimize or eliminate dusting, apply a commercially available chemical floor hardener, such as sodium silicate (water glass) or metallic zinc or magnesium fluosilicate, in compliance with manufacturer’s directions on thoroughly dried concrete. If dusting persists, use a coating, such as latex formulations, epoxy sealers, or cement paint
• In severe cases, a serviceable floor can be obtained by wet-grinding the surface to durable substrate concrete. This may be followed by properly bonded placement of a topping course. If this is not practical, installation of a floor covering, such as carpeting or vinyl tile covering, is the least expensive solution to severe dusting

• Use moderate slump concrete not exceeding 5 inches [125 mm]
• Ensure that there is adequate venting of exhaust gases from gas-fired heaters in enclosed spaces
• Do not broadcast cement or sprinkle water on concrete prior to or during finishing operations

• Do not start finishing operations while the concrete is bleeding
• Use adequate curing measures to retain moisture in concrete for the first 3 to 7 days and protect it from the environment, especially freezing conditions