Start with the wall, not a bottle of cleaner
A green or dark mark may look like a straightforward cleaning problem, but its location and the condition of the finish matter. Describe where it appears: below a gutter, near planting, across a shaded wall or around a fitting.
Do not assume that every mark has the same cause. Cleaning visible contamination is different from resolving a defect that allows persistent moisture to reach the wall.
Identify the finish if possible
Render systems, painted surfaces and repairs can have different care requirements. If you know the manufacturer or have installation information, keep it available for the contractor. A wide photograph and a close view are useful when you do not know the precise finish.
Tell David about cracks, flaking areas, recent patching or internal signs of damp. These may need investigation before cleaning is appropriate.
Questions about the method
Ask how the proposed method has been chosen for the surface, whether a test area would be useful and how the surrounding features will be protected. Any treatment should follow its product-specific instructions.
Nearby planting, vents, outside sockets and neighbouring boundaries should be part of the discussion. A cleaning plan needs to consider more than the central patch of staining.
Decide what result is realistic
Surface build-up may be treatable, while permanent staining or variations in the render may remain. A useful quotation explains likely limitations instead of promising that every wall will look newly finished.
Where a leaking gutter appears to be contributing to the pattern, address that issue as part of the wider plan. Gutter cleaning can deal with debris; damaged guttering requires suitable repair advice.
Arrange an assessment-led quote
See the render-cleaning service and contact David with the postcode, wall photographs and any finish details. The aim is to agree an approach that fits your property and to identify questions that cleaning alone cannot answer.