Cement and mortar contain lime. In normal circumstances, this reacts during the curing of the mortar to form insoluble, hard chunks that hold the bricks in place. In some cases, however, some of this lime can dissolve and form run-offs.
Lime typically starts to bubble when it comes into contact with an acid such as vinegar. Drip some vinegar on an affected brick and if it bubbles, then you know. Always do the test on the surface of a brick and not on a joint, because mortar always contains lime!
Remove as many run-offs as possible first with a stiff brush. Then get started with a high-pressure cleaner. In extreme cases, a (preferably) sulphaminic acid or hydrochloric acid-based façade cleaning agent must be used.
Allow the façade to dry for at least 24 hours after cleaning and then impregnate with WP7-401 Façade waterproof. This means that no more water can penetrate into the joints and no new run-offs will form.
