What is Red, Green & Black Algae?

The red, green or black algae that is commonly seen on homes throughout Inishowen is technically a Biofilm.

A Biofilm can consist of any combination of algae, mould, mildew, fungi, yeasts and protozoa that stick to a surface, establish their roots, and grow and multiply photosynthetically.

These microorganisms thrive on porous surfaces in damp humid conditions which means that the vast majority of buildings and exterior wall finishes are likely to form some sort of biofilm colonisation over time in our climate.

If left untreated this biofilm will continue to grow, working its way inward to degrade the physical integrity of the surface and outwards making it more visible and affecting the surface’s ability to repel water.

Red algae, or trentepohlia, can be one of the toughest forms of algae to remove. If left untreated it forms a tough biofilm layer which power washing alone can’t resolve.

One common DIY solution is to attack it with bleach, but whatever positive results this may appear to achieve, they are only temporary; those unsightly red stains reappear after a relatively short period of time. Furthermore, this method can damage or stain the surface due to the highly corrosive nature of the bleach and more importantly; Pets, children, nearby plants and the Applicator themselves are put at risk for the same reason.

Red algae is adaptable and very resilient, thriving on basically any surface where it can latch onto and grow such as pebble dash, render, k-rend, brick, paint, wood, PVC cladding, natural stone and other surfaces. The species favours mild climates with plenty of rain and high humidity, meaning areas like the north west of Ireland are ideal hinterlands.

Green algae or cyanobacteria is a type of phototropic microorganism, so named for its use of sunlight as an energy source. They form a dense mucous-like membrane as they multiply, eventually assuming a furry fibrous texture that covers surface areas completely. Even high-quality masonry paints with anti-fungal properties can be colonised when environmental conditions prevail.

Phototropic microorganisms can be some of the most unsightly of surface biofilms, appearing in a bright green colour that really detracts from the overall look of a house. Their fine, fibrous quality clings fast to porous surfaces, making it very difficult to completely eradicate by power washing alone.

Species include:

– Desmococcus olivaceus
– Haemaotococcus pluvialis
– Cyanobacteria Nostoc sp.(Devil Spit)
– Filamentous Cyanobacteria

Chemoorganotrophic fungi or black mold favours natural stone surfaces and paving although it can also be commonly found on pebble dash and render/k-rend walls. Like all fungi, it grows through the downward penetration of roots that form sub-surface networks called mycelium.

If left untreated this can decay the surface and cause long-term damage to a building’s exterior while the surface pigmentation also becomes more and more prominent as it grows.

Traditional power washing is largely ineffective for the treatment of black mold. Although it may appear to show some short-term relief of the problem, this can actually help the fungi spread by agitating and releasing the spores into the atmosphere.

Moss is a type of non-vascular plant that grows naturally on just about any surface, including walls, kerbs and most commonly on roofs. It produces tiny spores that become air-borne and land on roofs and other prospective growth sites. During the moist, cooler months, these spores grow into moss.

Once establishing a colony on any rooftop, moss can wreak havoc in a number of ways. If left to grow, sufficient volume of moss can move and dislodge roof tiles as it expands. Weather can cause it to break off, roll down into the gutters and block them over time.

Moss also absorbs a lot of rain water which can become heavy and put a lot of extra load on the roof structure itself. Moss can also serve as a vehicle for capillary action, carrying water up and under fixings and tiles and accelerating water erosion. This is especially damaging during frosty weather in the winter months where the freeze-thaw effect can cause a lot of damage to tiles and slates.