White powder and white marks (efflorescence)

White powder or white streaks rise to the surface of stone, tile or concrete.

Key points

White powder and white marks (efflorescence) are components in the material or mortar that dissolve in water, are carried to the surface, and harden there. We remove them in a way that does not damage the material, and apply a treatment that makes the surface less likely to absorb water. Water coming from inside or from behind cannot be stopped by a surface treatment, so we may separately suggest repairing where the water gets in.

The photograph is one example. We decide on the cause after checking on site.

Possible causes

Substances in the material or mortar dissolve in water, are carried to the surface, and harden there
Rainwater or water from the ground is getting in through joints or from behind

What we check on site

Where the water gets in, and where it comes out
Where and when the white marks appear
The condition of joints and cracks

We do not decide on the cause, or whether the work can be done, from photographs alone.

How we deal with it

Remove the white marks by a method that does not damage the material
Apply anti-soiling treatment that makes the surface less likely to absorb water
Advise separately on repairing joints or cracks where water is getting in

What it cannot do

Water coming from inside or from behind cannot be stopped by a surface anti-soiling treatment. We cannot say that all efflorescence will go away

Before you try it yourself

Acidic detergents dissolve the white marks but can damage stone and joints. Do not use them on marble in particular.

What affects cost and time

It varies with the extent, how the water gets in, and whether repairs are needed.

The on-site survey and estimate are free. Where there are costs, such as for distant locations or when scaffolding is needed, the installer in charge will tell you in advance.