Leachates
Leachates are liquids that can seep through, or drain from, pavement materials, carrying dissolved or suspended particles. These substances can include minerals such as calcium, iron, and lime, which leave a white or brown crust that can be difficult to remove.
They are most commonly found where drainage has not been managed correctly, at the back of steps, and on step risers, also where vacuum-packed permeable brush-in sand jointing material has been used on a patio, and the drainage has not been considered in the base and sub-grade, or if a permeable bedding mortar has not been installed beneath the paving.
(See also Sulphates and Their Effects on Concrete.)
