laitance


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laitance

[′lat·əns]
(materials)
Weak material, consisting principally of lime, that is formed on the surface of concrete, especially when excess water is mixed with the cement.

laitance

The accumulation of fine particles on the surface of fresh concrete resulting from an upward movement of water in the concrete; occurs when excessive water is used in the mixing of the concrete.
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Laitance still forms at the surface of this type of material, so it must be removed with any curing compounds prior to coating application.
However, because these resurfacers are fundamentally hydrolyzed cement, a laitance layer can still form and should then be removed before coating application.
Consequently, the laitance layer that otherwise forms through the troweling action now is reacted with an epoxy polymer and provides sufficient tensile properties for adhesion of subsequent coating applications.
Laitance is a loose or powder layer of material on top of concrete.
This removes the paint, rust or concrete laitance, which is then drawn away with any dust to a filter plant or industrial vacuum cleaner.
In the footing, deep pockets of laitance and large voids extended beneath the pier along this face.
The coring program disclosed quality problems that included segregated sand or coarse aggregate, zones of trapped laitance, voids, and honeycombed concrete.
4 mm thick with compatible structural adhesive including surface preparation ( grinding of concrete substrate, cleaning it with wire brush, removing oil, laitance if present), profiling in parabolic manner or as per design requirement (applying compatible printer on prepared substrate.
The cause may be application of an unsuitable coating, presence of a hardener in the concrete, moisture or alkali migrating to the concrete-coating interface, crumbling of old concrete, or concrete that had grease, oil, wax, and/or laitance (cement and aggregate fines) on the surface before being painted.
Before painting, scrubbing with a strong detergent and a bristle brush followed by vacuuming will remove light deposits of laitance and improve bonding.
The preferred method of preparing new concrete is to remove this laitance through mechanical means such as grinding, sandblasting, and mechanical scarification, followed by vacuuming to remove all dust and loose material.