Bleed water carries fine cement particles, aggregate dust and impurities to the top, where they settle as a soft film with almost no strength. Laitance has to be removed by grinding, shotblasting, wire brushing or green cutting before a topping, overlay or the next lift goes on, or the new layer bonds to a weak skin and delaminates. Over-wet mixes and heavy bleeding produce the most.
Shotblast the laitance off the whole deck before the topping, I don't want to be back here chipping delams.
Also heard as
- surface laitance
- scum
Related terms
Bleed water
Water that rises to the surface of fresh concrete as the heavier solids settle.
Cream
The cement paste and fine sand that finishing tools bring to the surface, giving finishers something to work.
Construction joint
A planned stopping point between two placements, prepared so the next pour bonds to it or transfers load across it.
Delamination
A surface layer that has split away from the concrete below it, found by the hollow sound it makes when tapped.
Dusting
A soft, powdery concrete surface that rubs off under traffic or a scraped fingernail.