When coloured concrete is being compacted and finished, excessive mixing water brings the finer grains of cement and sand to the surface to create laitance - a weak, unsound, low-strength, often dusty, light-coloured whitish ‘skin’ of cement ‘scum’. The material at the surface is lighter in colour than that below the surface - so much so that when the concrete has hardened most lay persons believe the pigment has faded. A surface with laitance is weak, is possibly crumbly and has poor abrasion resistance after the concrete hardens.
A fluid mixture of water, cement, and fine sand that appears at the top of concrete soon after pouring
a layer of weak nondurable material containing cement and fines from aggregates, brought by bleeding water to the top of overwet concrete. Laitance may be detected by scraping the concrete surface with a putty knife; if a quantity of loose powdery material is observed or easily removed, excessive laitance may be considered to be present.
A residue of weak and non-durable material consisting of cement, aggregate, fines, or impurities brought to the surface of overwet concrete by the bleeding water
An accumulation of fine particles, loosely bonded, on the surface of fresh concrete, caused by the upward movement of water. This laitance must be removed before applying a topping.
An accumulation of fine, powdery aggregate particles on fresh cement caused by the upward movement of water; indicates that too much water was used in the mix resulting in poor surface adhesion for a waterproofing layer.
Surface material on top of concrete made up of fine cement and aggregate particles. It is loosely bonded and of low strength and must be removed by wire brushing before coating can be applied.
A layer of weak and nondurable material containing cement and fines from aggregates, brought by bleeding water to the top of overwet concrete, the amount of which is generally increased by overworking or overmanipulating concrete at the surface by improper finishing or by job traffic; effluorescence.
White dusty surface film which occurs when there is too much water, left to evaporate, in the concrete mix, or when it has not been worked properly during finishing.