A rendered wall that has gone green, streaked or spotted is almost always a cleaning job rather than a rendering job, and the work is decided by chemistry rather than by pressure. Two Atlas sheets were read this session — the Mykos Plus biocidal concentrate and the SZOP 2000 polymer-residue cleaner — and every method figure below is copied from them.
The Renders World render cleaning range holds three consumables, and the first decision is which of them the staining actually calls for. Where staining sits alongside cracking, the cause is behind the surface rather than on it, and the render cracking guide covers that route instead.
Identify What Is on the Wall Before Opening Anything
How to clean silicone render without damaging surface finishes starts with a diagnosis rather than a product, because the Atlas sheets scope their three cleaners to entirely different contamination and two of them are wrong on a render face. Reading the wall correctly is most of the job.
- Green, grey or black film on shaded elevations: algae, fungi or lichen. This is the one the biocidal concentrate is made for, and the one that genuinely belongs on a rendered facade.
- Paint, primer or dispersion render splashes: polymer residue from adjacent work. The SZOP 2000 concentrate is scoped to this, on the surfaces named below.
- White crystalline bloom near the base or around repairs: efflorescence, a salt-migration problem rather than a surface one. Diagnosis comes first here, and the efflorescence and white stains guide sets out the moisture path that has to be settled for any clean to last.
Reddish biological staining behaves differently from green, and the red and green algae identification guide carries the visual markers. Getting this stage right is what keeps a consumable from being spent on the wrong contamination.
Treating Algae, Fungi and Lichen on a Rendered Facade
Atlas Mykos Plus is a concentrated fungicidal and algaecidal preparation based on surfactant biocides, and its sheet declares it for building facades including those of thermal insulation systems, renders, concrete, limestone and stone. Rendered EWI sits squarely inside that scope. It holds biocide marketing authorisation No 7371/18, with alkyl (C12-16)-dimethylbenzylamine at 2.40 g/100 g and 2-octyl-2H-isothiazol-3-one at 0.24 g/100 g as actives, and it penetrates a few millimetres into absorbable mineral substrates rather than sitting on top.
The sheet sets out five stages, and the order matters more than the speed.
- Find and remove the damp source. The sheet opens here, naming horizontal or vertical damp proofing, roof flashing repairs and proper ventilation. Treating a wall while the moisture continues is what produces a short-lived result.
- Pre-clean the infected surface. Limited growth is brushed off and vacuumed; very tough infection is removed mechanically. The sheet allows a pressure washer at this stage, with the technique matched to the surface and the degree of contamination.
- Apply uniformly and profusely. Brush, painting roller or sponge, working until the surface is completely moist, then leave it for at least 6 to 12 hours. Dilution is maximum 1:5 with water, and heavy organic growth calls for a smaller ratio.
- Repeat three times. Fungi are present at different growth stages, and resistant spore forms such as conidia survive a single pass, so the sheet recommends three applications with a 12 to 24 hour break between each.
- Wait 48 hours before finishing. Painting and other finishing work start no earlier than 48 hours after application.
One figure decides whether the treatment works, and it is easy to miss. The sheet declares a biocidal effect against algae and mould at a minimum of 150 g/m², while stating consumption as 0.02 litres of concentrate per m² per single application. At the maximum 1:5 dilution, one pass delivers roughly 0.12 litres of solution per square metre — below the declared threshold. Take the stricter reading: dilute less generously than the maximum, or commit to the full three-pass protocol, which is what the sheet is describing when it recommends both together.
The follow-on is documented too. The sheet recommends finishing with a silicone or silicate paint to reduce substrate absorptivity and limit the risk of further contamination, naming ATLAS SALTA N — so the silicone masonry paints range is the manufacturer's own route after treatment rather than an upsell. Confirm the variant when ordering, since the bucket stocked here is ATLAS SALTA.
Removing Paint, Primer and Dispersion Render Residue
The SZOP 2000 concentrate contains non-ionic surfactants, solvents and alkaline agents, and its sheet scopes it to residue from dispersions — stains from priming preparations, emulsion paints and dispersion renders. That makes it the clean-up product for the marks left behind while a facade is being finished.
Its surface list is specific, and it is not the render face: ceramic tiles including glazed, terracotta, porcelain and clinker, stone surfaces, sanitary ware, chromed and lacquered surfaces, stainless steel and plastics. The sheet also advises against using it on timber and glazing, and recommends a trial clean where there is any doubt.
- Dilution: up to 1:5 with water depending on how heavy the soiling is, spread onto the surface.
- Heavy marks: saturated with the liquid undiluted.
- Dwell: left for 15 minutes in every case so the liquid can start working, then worked with a stiff brush and repeated if needed.
- Rinse: the whole area washed thoroughly with water afterwards.
- Conditions: substrate and ambient temperature +5 °C to +30 °C; density approximately 1.0 g/cm³; tools cleaned with clean water immediately after use.
- Shelf life: 12 months from the production date on the pack.
Consumption is stated as dependent on the degree and character of the soiling, so no coverage rate is published here. The sheet notes the product is not classified as a construction product.
What Not to Put on a Render Face
The acid cleaner in this range is the one most often reached for by mistake. Atlas Cement Away SZOP is an inorganic-acid concentrate scoped by its sheet to acid-resistant surfaces — ceramic tiles, stone, chromed, lacquered, stainless steel and plastic. Render is not among them, and the sheet notes that absorbent porous surfaces into which soiling has penetrated are difficult to clean.
Treat it as the product for the tiles, sills and fixtures adjacent to a rendered wall rather than for the wall itself. Where a white bloom is sitting on the render, the answer is the diagnostic route rather than an acid: establish whether it is efflorescence and where the moisture is coming from, because the deposit returns until that is resolved.
Two general cautions apply to both concentrates. Gloves, eye and face protection and protective clothing are specified, and the biocide is very toxic to aquatic life with long-lasting effects, so release to the environment is avoided, spillage is collected and containers go to authorised disposal. Both sheets ask for a trial application on a less exposed area before committing to a facade — worth doing on any render whose exact formulation is unknown.
Key Takeaway: Match the chemistry to the contamination. Biological growth on render takes the biocide, applied to a moist surface, left 6 to 12 hours, three passes at 12 to 24 hour intervals, with the damp source fixed first. Paint and dispersion residue takes the alkaline cleaner on hard surfaces. The acid cleaner stays off the render face.
Keeping a Cleaned Facade Clean
Recolonisation is a moisture story, and the sheet's own opening instruction is the strongest preventive measure available: find and remove the damp source before anything else. Everything below follows from that.
- Deal with the water first. Damp proofing, roof flashing and ventilation are the three the sheet names, and a wall that dries between rainfall is a wall that resists growth.
- Use the residual effect. Mykos Plus is declared as having a preventive action protecting surfaces against the development of biological corrosion, so a correctly dosed treatment is doing work after the visible growth has gone.
- Finish with a reduced-absorption coating. The silicone or silicate paint the sheet recommends is a preventive step, not just a cosmetic one.
- Keep planting off the wall. Airflow at the base lets the surface dry, which is the condition growth needs and does not get.
- Store the concentrate properly. Between +10 °C and +30 °C, out of direct sunlight, protected from freezing, stirred thoroughly before use — 24 months from manufacture under those conditions.
For the schedule these washes fit into, the render maintenance guidance covers intervals and renovation routes, and the rendering materials range holds the finishes that go back on afterwards. The trade desk at Renders World can confirm a dilution and a quantity against a measured elevation before anything is ordered.
Written by Mariusz Saja. Technically reviewed by Renders World Team. Last reviewed Aug 2026.
FAQ — Dilution, Quantities and Compatibility
Can a pressure washer be used on silicone render?
The Mykos Plus sheet permits mechanical cleaning including a pressure washer, both for pre-cleaning the infected surface and for removing stains after the dwell period, with the technique adjusted to the surface and the degree of contamination. It sets no pressure limit, and no figure in bar is published here because no sheet read this session states one. The chemistry does the work, so the gentlest technique that lifts the residue is the sound choice, confirmed on a trial area first.
How much biocide does an elevation need?
Consumption is 0.02 litres of concentrate per m² for a single application. A 60 m² gable therefore needs 60 × 0.02 = 1.2 litres per pass, and 1.2 × 3 = 3.6 litres across the three passes the sheet recommends, so one 5-litre pack covers it with margin. The concentrate also comes in 1-litre packs for smaller work, and heavy growth calls for less dilution, so allow headroom on badly weathered walls.
Is it safe on render over EPS or mineral wool?
The sheet declares the product for building facades including those of thermal insulation systems, along with renders, concrete, limestone and stone, and describes it as safe for cleaned surfaces. It also recommends a trial application on a less exposed part of the surface to establish how a particular finish responds, which is worth doing on any render whose formulation is not certain.
How soon after treatment can the wall be repainted?
Not earlier than 48 hours after application, for painting and any other finishing work. The sheet recommends silicone or silicate paints for the new finish because they reduce the substrate's absorptivity and limit the risk of further contamination, naming ATLAS SALTA N — so the repaint is part of the treatment rather than a separate job.
Can the same product be used indoors?
The sheet covers indoor and outdoor use for walls and floors, but routes laundries, bathrooms, kitchens and swimming pools to Atlas Mykos No. 1 instead. Where it is used indoors, rooms are not brought back into use until 48 hours after application, and respiratory protection is specified where ventilation is insufficient.
What precautions apply around planting and drainage?
The biocide is very toxic to aquatic life with long-lasting effects, so the sheet asks that release to the environment be avoided, spillage collected, and containers disposed of through authorised companies. Protective gloves, clothing, eye and face protection are specified. Brush application gives more control than spraying where there is planting at the base of the wall, and confining the product to the treated area is what keeps runoff manageable.