Quick answer: Commercial render and cladding cleaning on large buildings -- office blocks, industrial units, social housing blocks, schools and retail premises -- requires softwash technique rather than high pressure, the correct biocidal solution for the growth type, appropriate access equipment, and compliant management of biocide-containing runoff. High pressure on modern render systems (K-rend, Parex, Weber, monocouche) causes surface damage and voided warranties. The correct method is low pressure application of a biocidal solution, appropriate dwell time, and a low pressure rinse. Biocidal products used commercially must be correctly classified under GB CLP -- non-toxic or eco-friendly claims on commercial biocides are non-compliant under BPR. This guide covers the complete commercial softwash process.
Commercial render and cladding cleaning is a growing market driven by the increasing use of thin-coat render systems on modern commercial buildings, the Decent Homes Standard maintenance obligations for social housing external fabric, and the aesthetic and property value requirements of commercial property management. It is also one of the most technically demanding pressure washing applications -- done incorrectly it damages expensive render systems, creates environmental liability from biocide runoff, and creates working at height risk.
Why softwash -- not high pressure
Modern thin-coat render systems -- K-rend, Parex, Weber monocouche and similar -- are designed to be maintained by low pressure washing. High pressure washing:
- Forces water behind the render system, undermining adhesion and causing delamination
- Damages the surface texture of through-coloured renders, creating inconsistent appearance
- Voids manufacturer warranties on warranty-backed render systems
- Does not kill algae, lichen and black mould at the root -- it removes surface growth while leaving the spore base intact, causing rapid re-growth
Softwash works differently. A biocidal solution is applied at low pressure (typically below 100 psi), allowed to dwell on the surface for the time required to kill the biological growth at the root, and then rinsed at low pressure. The biological growth dies and washes off during subsequent rainfall, or is rinsed off after the dwell period. Re-growth rate is significantly slower than after high pressure washing because the root biological matter has been killed rather than physically removed.
Biocide selection and compliance
The choice of biocidal solution for commercial softwash depends on the growth type:
- Green algae -- the most common external growth on render. Sodium hypochlorite dilutions or quaternary ammonium compound (quat) based biocides are effective.
- Black mould (Cladosporium, Alternaria) -- requires a biocide specifically effective against black moulds. Some algaecides are not effective against black mould species.
- Lichen -- the hardest to treat. Lichen is slow-growing but deeply attached. Biocidal treatment kills lichen but the physical remains take longer to wash off. Multiple treatments over a season may be required for established lichen.
- Moss -- responds well to biocidal softwash. Dead moss should not be pressure washed off immediately after treatment -- it will wash off naturally or can be brushed off gently once dead.
All biocidal products used commercially must comply with the Biocidal Products Regulation (BPR). Products marketed as non-toxic, safe or harmless cannot be legally described this way if they contain biocidal active substances -- these marketing claims are non-compliant under BPR. From August 2026, updated GB CLP classifications apply. See: Biocide labelling compliance
Access methods for commercial buildings
- Up to 4m -- ground level with extended lance: most ground floor facades and single-storey industrial units can be softwashed from ground level with an extended lance and appropriate nozzle.
- 4-10m -- telescopic water-fed pole: softwash delivered through a telescopic pole system from ground level avoids the need for access equipment on many two and three-storey facades.
- Above 10m -- MEWP (cherry picker): for multi-storey commercial buildings, a MEWP provides safe working access. Work at Height Regulations 2005 apply -- risk assessment and method statement required. The MEWP operator must be trained and the machine inspected before use.
- Rope access: for buildings where MEWP access is not possible (listed buildings, restricted access, complex roof geometry), rope access operatives with IRATA qualifications provide the correct access solution.
Biocide runoff management
Biocide-containing runoff from commercial softwash is environmentally sensitive. The active biocidal substances in softwash solutions are toxic to aquatic organisms at low concentrations. Runoff must not enter surface water drains, watercourses or permeable ground. On commercial sites where softwash runoff will drain toward surface water, containment measures are required. See: Environmental Permitting guidance
Related guidance
Cleaning trade hub | Social housing hub | Biocide labelling compliance | Environmental Permitting | Chemical reclassification August 2026 | Petrol pressure washers for softwash
