What Is the White Powder on Concrete Paving Blocks? Understanding Efflorescence (Lime Bloom)
[Engineering Facts Series] When inspecting precast concrete footpath or roadway paving blocks, many in the construction trade have come across a white powdery deposit on some block surfaces — even within the same selected batch, some blocks show it while others do not. This is a normal, natural characteristic of cement-based products. Its technical name is efflorescence , commonly known as "lime bloom" or "white frost", and it is not a quality defect . This article explains the phenomenon from a scientific standpoint, with reference to international standards. What is efflorescence? Efflorescence is the appearance of a white, powdery or frost-like deposit on the surface of cement-based products. It forms when soluble salts — principally calcium carbonate — migrate with moisture to the product surface and crystallise. It is a surface phenomenon only, and does not affect strength, abrasion resistance or slip resistance. The science: cement hydration and ...
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