Efflorescence: What is it and What Does it Mean For Your Roof

What is Efflorescence?

Efflorescence is a crystalline deposit of salts that can form whenever water is present in or on concrete as well as brick, stone, stucco, or other surfaces of building materials. The efflorescence sports a white, or sometimes, gray-colored tint.

The salt deposit will remain on the surface of the material, including concrete roof tiles, until the water evaporates. Efflorescence will also appear as a white powdery substance when it forms on walls and floors, and it requires special treatment to remove.

These salts deposits are made of calcium hydroxide, which is a compound that can be found in concrete products. When the calcium hydroxide reacts with carbon dioxide in the atmosphere it forms calcium carbonate crystals, so the little white dots or patches you may see on a roof are the result of this process. 

Efflorescence on Concrete Roof Tiles

When construction materials contain concrete, small amounts of calcium hydroxide in the concrete can transfer to the surface of the material, which is why the calcium hydroxide can react with the carbon dioxide in the air.

The crystals are very sparkly, which is how it got its name efflorescence since the calcium carbonate fluoresces.

Is Roof Efflorescence Harmful?

Roof efflorescence is not harmful, and the little white crystals can even form immediately after the roofing tiles are created and other concrete materials. The calcium carbonate will normally disappear over time.

The roof efflorescence does not negatively affect the integrity of the building materials and they will remain strong and stable. The issue is that roof efflorescence is not an attractive look on the roof of your house or business, and it is not always evenly spread out, so it looks out of place.

How to Remove Efflorescence?

It is possible to remove roof efflorescence by using products that have been created for this purpose. Efflorescence is removed by natural weathering processes – as rainwater is slightly acidic, it gradually dissolves and washes away the deposits. The process may also be assisted by warm dry weather when the deposit is blown away. Although it is impossible to state exactly how long efflorescence will take to be removed by the weather.

Roof efflorescence can appear not only on outdoor surfaces but also on indoor surfaces, and its frequency and intensity may vary from place to place or time to time, depending on moisture levels and the temperatures present.

Three conditions can facilitate the formation of roof efflorescence, including if there are water-soluble salts in or on the surface of the material that is being used if moisture is present in enough of a concentration to allow the salt to become a soluble solution, and when salt moves to the surface of the material as the moisture level decreases.