What are the white crystals coming out of my brickwork?

[Fluffycloudland77]

& how do I get rid of them?

What is Efflorescence?
Efflorescence is often described as an ugly residue that is often seen after the construction has finished. In construction terms we use the word "Efflorescence" to describe a white residue left on the brickwork. It is important to note that this is a process in which any substance is carried by a liquid to the surface, we will concentrate on the carriage of soluble salts to the surface, the water evaporates leaving the salt behind as a white powder. Now where does the salt come from we ask – well that answer to that comes in many parts, salt can be present in the clay used to make the bricks or from the sand and cement used in construction, certain construction practices can be used to cut down on the on the quantities of soluable salts present in the wall.
How to prevent Efflorescence
Total prevention is not possible, but a few simples procedures can help to cut down on the amount Efflorescence that will be produced.
• All bricks stored on site should be kept clean and dry and not just left stacked in the middle of a field, waterproof sheeting should be used at all time and the bricks should be stacked on a hard well drained surface.
• Bricks that are loaded out on the scaffolding prior to laying should be covered and protected and not allowed to get saturated.
• Newly laid brickwork should not be allowed to get saturated, especially in the winter or early spring.
• In some instances i have seen and actually used the habit of actually wetting bricks and allowing them to dry a little prior to laying, this can make it easier to lay the bricks, but is fraught with future problems and should be avoided. One of the problems in today's modern world is adequate site management, alot of experienced professionals no longer seem to manage construction sites and the prevention of future problems seems to be of no interest until the problems show. There is no substitute for good site management and all companies should take heed.
How to remove Efflorescence
In my experience if you just introduce good site practices and make people aware of the causes, then alot of Efflorescence can be avoided. Using a stiff brush will often remove alot of the residue, but this is often not easy if you have a 2 or 3 storey building. Do not use anything abrasive, check there are no features that are allowing water to cascade down from roofs or gutters and in time it will diminish.

To summarise above; efflourescence. Occurs especially when building of a house has taken place during winter & the bricks have got wet. Stiff brush gets rid of some residue. It's not harmful.