Efflorescence
Efflorescence is the term used to describe the white, powdery substance that appears on the surface of natural stone paving slabs, which have been laid into a bedding mortar. This type of efflorescence is known as secondary efflorescence.
These deposits are caused by the migration of soluble salts travelling through the slab via capillary action. When water carrying dissolved salts evaporates on the surface, it leaves behind these salty deposits, resulting in the visible phenomenon.
A full mortar bed (See Full Contact Mortar Bedding) will often hep to prevent secondary efflorescence as any voids in the bedding mortar will collect water and salts via capillary action which will exacerbate the visible blooms.
Block pavers commonly experience this primary efflorescence, which occurs when water or moisture interacts with any soluble salts within the paving materials. When moisture evaporates, and the salts migrate to the surface, it leaves behind noticeable deposits. This usually occurs shortly after installation, and is frequently attributed to the initial cement hydration in the pavers. This primary efflorescence is completely natural, and usually disappears after a few months.
In itself, it is unlikely to cause any structural damage, and will clear with rainfall or brush cleaning. However, if it persists, it may indicate other problems with retained moisture within the build structure.
There are various types of efflorescence removal products available from Builders Merchants, but beware of applying acids without taking further professional advice.
Image courtesy of Global Stone Ltd.
