Wall Render

Cleaning Wall Render

Controlling the biofilm

The straight forward way of controlling the biofilm is by impregnating the surface with a solution of quaternary ammonium. The product AlgoClear® Pro works on the biofilm by puncturing microorganisms cell walls. It does not interact with the mineral components of self finished renders and does not contain any compound deleterious to the colouring agents or the surface cohesion. In particular, the product has a neutral pH. On porous render, the surfactant active will decontaminate deep into the surface porosity by capillary action.

Dispersion of the biofilm

Green Algae dies within minutes by cell wall puncture. If the algae film is thick, the dead cells display milky sheen for a few hours.

Trentepohlia is a green algae giving away a red dye. Chemically the red marks are a beta carotene and wash away readily under the rain. We sometimes find some grey under the darker red cones: It comes from a fungi taking advantage of the light filter provided by the beta carotene. Sometimes, after a prolonged period there is an accumulation of decayed organic material behind the red, revealed only after the stain has washed. It does not react to additional biocidal treatment. They are dissolved with MetaClear.

Filamentous fungi are characteristic black inverted cones under stone joints, window sills and cornices, or thinly spread over flat surfaces. The black is metabolised by the hypae in the porosity of the render and protects it from UV light. The paste is water soluble and decays by photolyse. Dark metabolites are dissolved with Metaclear.


Moulds are a group of filamentous fungi. Their structure enable them to key their filaments in the porosity of render and even rock. As a result, moulds do not self cleanse as readily as algae. The most common species of fungi on facades are the Cladosporium spp and Alternaria spp. Both metabolise a black pigment protecting them from UV radiations, and causing some staining of the surface. Moulds are killed by a solution of Algoclear within approximately one hour. The self-cleansing however can take several months, or is helped in a second visit by rinsing with fresh water.

The treatment of moulds is best carried out in steps. First remove the thick with a scraper until the substrate is clearly visible. Apply a 1/20 solution of AlgoClear® Pro using a soft bristle brush. This helps softening the biofilm. After brushing, a rapid rinsing with a solution 1/20 AlgoClear® Pro will complete the second step. About 6 weeks after the treatment the black discolourations should have significantly receded.

It is good practice to leave the surface to shed the dead biofilm for 4 weeks to 6 weeks. This gives the superficial stains time to receed, leaving the marks requiring attention more identifiable.

The second visit may consist of a simple pressure water rinsing. The remaining metabolites are not alive. A second biocidal treatment will not succeed in reducing them. To do this a specific oxidising treatment is required. Contact the Manufacturer TVSP Ltd for details.

Biocide Purity

Biocide purity: It is particularly critical to use a high purity quaternary ammonium on render. Alternative biocides based on bleach or quaternary ammoniums containing impurities/solvents may permanently affect the appearance of the rendered surfaces.

Water repellents

Water repellents: They are sometimes used on stone or render to help keeping the surface dry. There is no evidence showing water repellents having beneficial effects with regard to the return of contaminants. As with paints, reducing the external porosity may lead to adverse effects on the inner envelope of the building.

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