4 Keys to Controlling Algae Growth and Fungus on Concrete Surfaces

Protecting Cementitious Surfaces with Algae Treatment and Fungus Treatment

Outdoor structures are exposed to many elements that cause wear and damage over time, even such durable surfaces such as concrete, grout or cementitious-based coatings. Fungus and algae growth on these surfaces will cause problems that are unsightly, unhealthy, costly to remediate, and can erode the underlying substrate. Full fungus and algae control over such unwanted growth requires a systematic approach to reduce the chances that an opportunistic fungus or algae can take root starting with the initial construct design through to long-term maintenance. Controlling algae and fungus growth on concrete structures requires a system that incorporates the following:

1. Proper Design for Water Control to Prevent Algae and Fungus Growth

One of the keys to fungus and algae prevention on concrete surfaces is to control the flow and presence of water. For exterior surfaces, this is primarily done with a suitable design that uses gravitational assistance to channel the water flow away from the structure. Figure 1 illustrates a wall design that properly controls water flow, significantly reducing the chances for fungal or algal contamination. If there is no contamination, then there is no need for fungus treatment or algae treatment.

Figure 1 – Good design elements of an exterior wall to reduce the chances for fungal or algal growth.

Algae Treatment

2. Good Workmanship Helps with Algae Control

Proper design can easily be defeated by poor workmanship and materials. Improperly mixed concrete will quickly crack and/or blister, allowing entrance to fungal spores and offering them foothold in the structure, which will require some type of fungal treatment. Figure 2 shows a column made of improperly mixed concrete – too much water in the mix has caused cracks to form in the surface, allowing fungal to infiltrate. As the fungus grows in the crack, it will push from behind, causing further blistering and more damage. Figure 3 shows a wall that is improperly sloped across the top to allow water drainage. Water collects on top of the wall where fungus and algae grow readily.

Figure 2 – Cracks in the concrete have broached the surface, giving fungus a foothold in the surface and ultimately requiring fungus treatment.

Figure 3 – The top of the wall is improperly sloped to drain, allowing water to collect and fungus to grow.


3. Microban® Antifungal and Anti Algae Technology

Particularly in areas with high humidity, low sunlight exposure and damp conditions, another layer of protection is often needed to prevent algae and fungus growth. Microban additives can be easily incorporated into cementitious materials such as grouts or highly pigmented cement coatings at low dosages, specifically for controlling algae and fungus growth. Efficacy has been demonstrated in outdoor exposure tests conducted in Florida; the results of one such test are shown in Figure 4. Untreated samples of a cementitious coating began to show fungal growth at 9 months, and a greater difference in treated and untreated samples was seen after 12 months. The samples were rinsed twice weekly with an acid solution to simulate pollution, accelerating aging by a factor of 6.5x; the 12-month sample suggests that the surface with fungus treatment and algae treatment would remain growth free for over six years.

4. Maintenance to Prevent Algae and Fungus Growth

Regular maintenance and cleaning should always be part of long term planning for a structure. Chips or cracks that develop for any reason should be quickly repaired to prevent algae or fungus growth from beginning to happen. Surfaces should also be cleaned on a regular basis to prevent algae or fungus growth. Any surface where dirt or grime can build up provides a place for fungus or algae to grow. The growth is actually on the surface dirt layer rather than the surface that contains the algae and fungus treatment, but it can lead to surface penetration once the growth is established, as shown in Figure 5.

Figure 4 - Untreated samples of a cementitious coating show fungal growth at 9 months, and a clear difference in treated and untreated samples was seen after 12 months. This demonstrates the functionality of the Microban additives to control algae and fungal growth for over six years due to the accelerative effects of a bi-weekly acid wash.

Figure 5 – Horizontal fence rails show a very high degree of visual contamination. On cleaning with water and a small scrub brush, this contamination is removed and the underlying Color Cement, protected by Microban, shows no signs of fungal or algae damage.



To prevent algae and fungus growth on concrete and cementitious masonry surfaces, a complete system approach that includes design, workmanship, cleaning, and additives that inhibit microbial growth such as Microban Antifungal Technology is required When all aspects are considered and properly performed, concrete surfaces will remain clean and free of unsightly and unhealthy growth for many years.