Efflorescence and Natural Stone: What it is and what to do about it.

Efflorescence on a patio next to a lawn

What is Efflorescence?

Efflorescence is a white, chalky substance that may appear on the surface of natural stone, clay brick, concrete paving or any other porous building material. Naturally-occurring salts found in soil, water, sand, gravel and cement are dissolved by rain and groundwater. This moisture is drawn to the surface of the stone where it evaporates, leaving the salts behind as a white haze.

Although unattractive, the process is completely natural and in no way damages the stone. Nor does it mean that the stone is defective in any way.

Efflorescence and Natural Stone

As professionals in this industry, we've all seen efflorescence before and recognise it for what it is - an unsightly but temporary inconvenience.

However, if you are a homeowner that has just spent a significant amount of money on natural stone, the appearance of efflorescence can leave you feeling less than satisfied with your paving.

Knowing about efflorescence in advance can help to reassure you if and when it occurs.

Efflorescence on natural stone and on a brick wall

How to Prevent Efflorescence

Although it is virtually impossible to eliminate all possibility of it occurring, several methods of installation can minimise the potential for and the intensity of efflorescence, including:

• Storing stone on pallets to keep it dry and off the ground.
• Ensuring proper grading and drainage to prevent water from sitting on the stone.
• Damp proofing below and behind installations, particularly when using porous material like natural paving
• Covering unfinished projects at the end of each day to prevent moisture behind the stone.

It's also worthwhile noting that less porous stones absorb less water and may, therefore, be less prone to efflorescence.

How to Clean Efflorescence off Natural Stone

In all but very extreme cases, efflorescence will stop as capillaries in the stone become blocked by crystallized salts. Once the process stops, the white deposits will eventually wear off with use and exposure. For clients who are in a hurry to remove it, water and a stiff-bristled (non-metal) brush will often do the trick. However, if the process of efflorescing has not stopped or the factors causing it are still present, the haze will return and will need to be cleaned again.
In particularly stubborn cases, efflorescence can be removed with an efflorescence cleaner. However, be cautious when using chemical cleaners. Use only cleaners that are specially formulated for natural stone. Use them only as directed and test them in an inconspicuous area first.

In most cases, the best course of action is also the easiest. Simply allow the process to take its course and, before long, the stone will return to its original beauty.

If you are concerned about efflorescence, speak to your landscaper before you choose your stone, or before it is laid.