Causes
• Premature Finishing- This brings excess water, cement, and fines to the surface, which weakens the paste.
• Carbonation- Open salamanders, heaters, or engines give off carbon dioxide, inhibiting the normal hydration process.
• Condensation- Can occur when the temperature of concrete on an inside floor made with cool materials rises slower than surrounding, more humid air- common in spring and fall.
• Inadequate Curing- "Dryout" will occur where there is not sufficient moisture to continue the hydration process of the Portland cement paste, producing a soft, weakened material.
Prevention
• Do not begin finishing operation until all free water has evaporated or been removed from the surface, so that the concrete will support the weight of finisher.
• Vent exhaust and/or fumes to the outside, provide adequate ventilation.
• When high humidity is anticipated, use heated concrete. Open windows for ventilation and use blower-type heaters or fans to increase air circulation. Delay finishing operations until free water on the surface has been removed, but do not allow surface to dry out.
• PLAN AHEAD- Provisions should be made by the contractor prior to the placing of concrete to assure adequate time for proper placing, finishing, and curing based on the existing conditions at the job site.