White render

The Algoclear Cleaning Process applied to white render

The first step is to list the different types of contamination observed.

If the main issue is the appearance of a green sheen or red streaks the process is the simplest and consist in soaking the material with
a solution of the ACP biocide. The algae responsible for the discolouration will be dead before the product has dried and rain washes the streaks quickly. If the contamination is relatively light a simple spray soaking the render is sufficient. If the cleaning works seems somehow overdue the applicator will have to brush the APC biocide / surfactant and rinse the foam before impregnating the render. Do not let a coloured sud dry on the render or adjacent materials.

When a red contamination is left for too long, a fungi will settle behind, taking advantage of lesser UV exposure. Upon natural cleansing of the red water soluble beta carotene a grey shadow mark will stay.

Grey & black marks: Removing fungal metabolites is done using a mix of techniques.

The Algoclear Cleaning Process applied to white render

Metaclear: The gel is sprayed or brush applied. It has good adhesion. After a few minutes the gel stops working : It needs agitating. This will renew the active interface and collect removed contaminants. After a few minutes of second dwell time the render is rinsed.

The intensity of the gel treatment depends on the amount of metabolite to remove. A thin grey layer may only need coating and one dwell time before rinsing. If the grey is deeper, the gel will need agitating as above. If the black marks are long established the process is repeated.

Metaclear & steam: Steam is often used to remove thick layers of metabolites where excessive amounts of chemical would otherwise be needed. When the wall is substantially free from growth the finishing will consist of an application of Metaclear, eventually brushing after dwell time and steamed off. The flash application of heat on the gel provides the flash of detergency to the process.

Metaclear and pressure water. There is a risk inherent to applying pressure on a thin render particularly if there is insulation behind. For this reason we avoid it on render. However : With precautions a thin blade of pressure water will achieve good results in removing the bulk of a metabolite covering or lichen from stone. Ceramic nozzles will give a thinner water blade and the pressure reduced to about 15 bar, thus reducing the risk of damaging the substrate.

Red brown marks: They are usually clearly identified as rust marks and an acidic contact is the only chemistry available. Oxiclear is formulated for safe application on render. It is a gel preventing the acid from permeating the porous and alkali substrate. Care should be taken to monitor the dwell time. If left too long the gel may leave a slight colour difference with the rest of the elevation.

Tanin marks: They are not very common, but always delicate to remove. We find them below Cedar cladding, balcony decking, oak structures etc. After a gentle brushing with Oleoclear to remove ready soluble compounds Oozeclear will interact with the iron in the tanin and transform it into a soluble compound. The surface becomes bright pink during the iron conversion and needs re-applying until completion and rinsing. Oozeclear is very pungent and works most of the time.

Red Brown Marks

Accreditation: After a rigorous testing process the ACP biocide has been recommended by Kilwaughter Chemicals manufacturer of the self coloured render KRend.


How do I remove a small mark from a wall? Bird dropping or egg.

A professional would have a 5 litre drum of Metaclear at hand. For an individual removing a one off stain on render or a few black dots on stone the cost of a manufactured mixture is not always justified : A 4% bleach thickened with a few flakes of cellulose (wall paper glue ) will give a paste the viscosity of a pancake mix easy to apply and gently brush. Rinse profusely. The mix will not have the durability or detergency of Metaclear, but made one glass at a time comes at a nominal disbursement.

Before Render Cleaning - Softwash ScotlandAfter Render Cleaning - Softwash Scotland

Courtesy of Softwash Scotland

Thin Grey Layer on RenderThin Grey Layer Cleaned using Metaclear

Courtesy of Softwash Scotland

Red Streaks on RenderRender Cleaning using Oxiclear

Courtesy of RK Gutter Roof Conservatory Cleaning Ltd

Before Render CleaningAfter Render Cleaning

Outlook Property Services

Dirty RenderWhite Render Restored to its original color

Courtesy of Softwash Exterior Cleaning

Red Streaks on RenderWhite Render After Algoclear Cleaning Process

Courtesy of Softwash Exterior Cleaning

Sometimes the render finishes too close to the ground and takes a brown discolouration. This is generally an iron oxide from the soil. If the wall is also dirty, a first brushing with Oleoclear will remove all the contaminants except the iron oxide. The wall is now ready for a careful application of Oxiclear. Rinse generously as soon as the discolouration has receded.