Soluble Stains:

 

Bricks contain much soluble material often referred to as 'salts' or efflorescence. Usually the soluble materials remain within the bricks. However, occasionally the salts to migrate to the surface.

 

Those salts based upon the metals of iron or manganese are particularly unsightly and provide the stains illustrated in the photographs below.

 

Nevertheless a properly conducted cleaning operation can successfully remove the salts.