As cement and aggregate settle after placement, mix water is pushed upward and forms a sheen or puddles on a slab, a process called bleeding. Finishers wait for it to evaporate before floating or troweling, because working it back in weakens the top layer and leads to dusting, crazing and scaling. Cold weather, retarders, lean mixes and a vapor retarder directly under the slab all make bleeding last longer.
Don't touch it yet, there's still bleed water sitting on the low side by the dock door.
Sprinkling dry cement on bleed water to soak it up is a classic rookie move and a reliable way to get a dusting floor.
Also heard as
- bleeding
- bleed
- sheen
Related terms
Laitance
The soft, chalky skin of fines that bleed water leaves on top of concrete, too weak to bond to.
Floating
The finishing step that levels, compacts and opens the surface of a slab once the bleed water is gone.
Dusting
A soft, powdery concrete surface that rubs off under traffic or a scraped fingernail.
Blistering
Hollow bumps that form on a troweled slab when air or bleed water gets trapped under a sealed surface.
Vapor retarder
A plastic sheet under a slab on grade that slows ground moisture from rising into the concrete.