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May 29 - June 1, 2018

What causes concrete “dusting,” and is there any way to prevent or remove it?


Selected Answers

From Michael Quaranta of OPERATIONS 40 on June 1, 2018:
The question relates to the existing surface condition and it may be part of the new subject with OSHA's silica rulings. The best advice is to address the existing condition by removing the "fines" that are causing to condition. Bead blast to reveal the aggregate and apply a water-based liquid alloy sealer coating product. There are a few water-based epoxy sealers on the market today. You can forget all of the other "recommendations" because the problem needs to be resolved and not just treated.

From Zenith Czora of Zen Consultancy on May 29, 2018:
Dusting of concrete surfaces occurs when the surface is wearing out due to its weakness and the matrix is not properly bonding the fine aggregate particles, resulting to poor abrasion-resistance. Concrete dusting is caused by inappropriate concrete specification, excess addition of water required by the concrete mix design, premature finishing while bleed water is still on the surface, excessive water during finishing, rainwater, inadequate curing, inadequate compaction, the use of dry cement to soak up surface water, and freezing of the surface. To prevent the occurrence of dusting, the following actions are necessary. 1. Ensure the right specification for concrete strength. 2. Avoid adding excess water to concrete mix 3. Do not overwork the concrete. 4. Do not perform any finishing operation with bleed water or rainwater present on the surface. 5. Remove bleed water by using a rubber squeegee. 6. Do not sprinkle or trowel dry cement into the surface; 7. Finish the surface with a helicopter float.  8. Ensure proper curing of the newly laid concrete by coating the surface with an appropriate membrane-curing compound or covering the surface with a polyethylene sheet to keep the surface continuously damp for three to seven days. Depending on the severity of concrete dusting, dusting can be rectified by applying a dust proofer/inhibitor. Dust proofer/inhibitor is commonly a sealer based on a very hard styrene acrylic copolymer with a Tg of 56o C. Another  surface treatment is the application with chemical concrete densifier/hardener, which is based on a mixture of lithium and sodium silicate. This type of densifier reacts with the calcium hydroxide in the concrete to produce additional cementitious compounds, but they are only applied to the concrete that is at least 28 days of age and more. In more severe case, complete removal of the weak surface layer by grinding back to sound concrete may be required. Then apply an appropriate topping at a thickness of at least 10 mm  that would bond to the existing ground concrete. Application of suitable functional floor coating/covering to sound concrete would also prevent the concrete surface from dusting.

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Tagged categories: Concrete


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