Quats is the common abbreviation for quaternary ammonium compounds: surface-active substances used as cleaning, disinfecting and algae-control agents. In construction you meet them in products for cleaning and treating thatched roofs, roof tiles, façades, patios and timber.
Quats work because the active substance penetrates the cell wall of algae, mosses and fungi and damages the cell membrane, so the organism dies. Because the molecules also have soap-like, surface-active properties, the same substances appear in many cleaning and disinfecting products for kitchens, hospitals and livestock buildings.
Uses around the house
- Thatched roof — preventively and curatively against algae and moss growth
- Roof tiles — after removing moss, to delay its return
- Façades and render — against green growth on the north and shaded sides
- Paving and patios — against green growth and the slipperiness that comes with it
- Timber — as a component of wood preservative treatments
Using them sensibly
- Clean mechanically first — brush or wash off the loose moss and algae layer; the product works poorly on a thick layer of dirt
- Choose dry, overcast weather — rain within a few hours washes the product off, and strong sun dries it too quickly
- Dose according to the label — more is not better and only increases the environmental load
- Let it work — the effect usually shows only after weeks or months, because the dead growth has to be worn away by rain and wind
- Repeat periodically — growth returns in shaded places; a treatment every few years is more realistic than a one-off effort
What to watch out for
- Approval — biocidal products are subject to approval; only use products authorised for the application and follow the statutory conditions of use
- Watercourses — quats are harmful to aquatic organisms. Prevent rinse water from reaching a ditch, pond or gully
- Planting — cover plants below the work area and rinse them afterwards
- Pressure washers — do not use on thatch, old pointing or soft brick; that does more damage than the growth itself
- Personal protection — gloves, eye protection and respiratory protection if a mist forms
Related terms
- Thatched roof
- Green growth
- Moss removal
- Wood preservation
- Façade cleaning
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