Commercial jet washing is not one setting pointed at everything until it looks better. It is a method chosen against a specific surface and a specific contaminant, carried out in a way that keeps the wash water out of the drains, and on most commercial sites it is the stage that decides whether the marking or coating that follows it lasts.
The two things that most often go wrong are worth naming up front, because they are the two questions worth asking a contractor. The first is pressure used as the only variable, which cleans a car park and damages a cladding panel with the same lance. The second is where the water ends up, which is a legal duty shared between the contractor and you as the site operator, not a detail left to whoever is holding the hose.
The four variables, not just the pressure.
Cleaning is the result of four things working together: temperature, mechanical force, chemistry and time. Turn one up and you can turn another down, which is the whole basis of matching a method to a surface. More heat means less pressure and less detergent for the same result.
The physics behind that is straightforward. Every 10°C rise in water temperature roughly halves the time a chemical reaction takes, so a 20°C rise cuts it to a quarter. Applied to oil, grease, fat and soot, hot water softens and emulsifies the deposit so it lifts and rinses rather than being blasted off, and the same job is typically done around a third faster than with cold water, with the surface drying quicker afterwards. Hot-water systems commonly work at around 80°C, with a reduced-flow, higher-temperature stage available for encrusted deposits and more delicate surfaces.
Cold water is perfectly adequate for general and light soiling where heat adds nothing, and on some substrates it is the safer choice. The point is that the decision is made deliberately rather than by default.
The method follows the contamination.
A survey of what is actually on the surface comes before any quote, because the contaminant dictates the method as much as the substrate does.
- Oil, grease and fuel spillage around bays, delivery areas and pump islands calls for heat and degreasing rather than more pressure.
- Tyre and traffic film, skid marks and ground-in dirt suit hot water applied through a rotary surface cleaner, which works inside a protective housing and gives an even, streak-free finish across large flat areas instead of the striping left by a lance in the wrong hands.
- Chewing gum around entrances and footfall routes responds to high temperature at low pressure, often with no chemical at all.
- Algae, moss and lichen on walkways and shaded car park levels are a slip risk more than an appearance problem, and need a method that removes the growth without polishing the surface underneath.
- Bird fouling needs heat for hygiene as much as for removal.
- Staining absorbed into a porous surface over years is an honest limit of the method. Some of it will lighten rather than disappear, and it is better to say that before the work than after it.
Surfaces set the ceiling.
The pressure and technique that lift moss off tarmac would open a cladding joint or strip a sealant line. Reading the surface first is the part of the job that protects you.
Tarmac, concrete, block paving and hardstanding will take a commercial clean, though block paving needs attention to the jointing sand and tarmac that is already fretting will shed more material if the pressure is wrong. Steel, aluminium and composite cladding, building frontages and signage are cleaned at controlled pressure, with the panels, joints and finish treated as things to protect rather than obstacles to blast past. Existing markings, coatings and sealants on a floor are part of the surface too, and a clean that damages them has cost you more than it saved.
Where the wash water goes is a legal question.
This is the part of commercial cleaning that rarely appears in a quotation and should. The Environment Agency's guidance is unambiguous: you must not allow run-off to enter surface water drains, surface waters or ground waters. Doing so causes pollution and can be prosecuted.
There are three lawful routes for wash water. It can be treated on site, ideally with the water reused. It can be discharged to the foul or combined sewer, but only with prior written consent from the water company, which is what a trade effluent consent is and which sets out what may be discharged and at what rate. Or it can be collected in a sealed unit and removed by a registered waste carrier to an authorised site. Anything else, including letting it find the nearest gully, is not a grey area.
In practice that means containment is planned before the work starts: catchpots and silt traps on the drains, settlement tanks where volume requires them, bunding, sealed collection, and correctly sized and maintained oil interceptors where petroleum or grease is present, as on a forecourt.
One counter-intuitive point is worth knowing, because it catches out sites that believe an interceptor covers them. Detergent disables an oil separator, so detergent-laden water must not be discharged into one. That is another reason to reduce or remove detergent by using heat instead, and where detergent is necessary it should be biodegradable and phosphate-free. Recovering water at source, using surface cleaners with integrated suction, supports the same outcome and leaves the surface much drier.
The duty here is shared. Responsibility sits with the cleaning contractor and with the site operator who engaged them, so both are expected to have satisfied themselves that the consents and containment are in place before a machine starts. The relevant legislation is the Environmental Protection Act 1990, the Water Resources Act 1991 and the Environmental Permitting (England and Wales) Regulations 2016, and enforcement runs to notices, fines and prosecution. Asking a contractor how they will contain and dispose of the water is not an awkward question. It is you protecting your own site.
Cleaning before marking or coating.
Markings and coatings bond to the surface, not to what is sitting on it. Anything left behind becomes the weak layer, which is why the cleaning stage is the one most often trimmed and the one that most reliably takes the finish down with it. Oil that has soaked in, tyre rubber, moss, and the film left by a site's own cleaning regime all have to come off before new material goes on, and drying time after washing belongs in the programme rather than being squeezed out of it.
Cleaning is not the same as preparation, and it is worth being clear about where the line falls. Washing removes what is on the surface. Where a coating is going on, or where old markings and previous coatings have to come off, the surface also needs mechanically opening up, which is shot blasting, grinding or scarifying rather than water. A clean surface is the condition for good preparation, not a substitute for it.
Frequency, and treating it as maintenance.
How often a site needs cleaning is driven by traffic rather than the calendar. High-use circulation areas, entrances and frontages may justify monthly attention, with quieter levels and outlying areas deep cleaned quarterly. Smaller, more frequent interventions generally cost less over a few years than occasional heavy washes, and they are gentler on the surface, its coatings and its sealants.
Timing matters as well. Autumn leaf fall and wet months leave the organic growth that becomes a slip risk, so a planned programme tends to work around the seasons rather than reacting to whatever a site walk turns up in February.
Keeping the site open.
Most commercial sites cannot close, so the work is phased, and it is commonly scheduled out of hours or overnight where the site demands it. That suits the cleaning as well as the trading, because a car park cleaned empty is cleaned properly, and wet surfaces have time to dry before anyone walks on them.
One team from the clean to the final coat.
The reason cleaning, preparation, marking and coating sit together is accountability. Where a coating lifts or a marking fails, a single contractor cannot point at the stage before it. C&R covers the whole sequence, which also means a pre-mark clean can be planned as part of the marking job rather than arranged separately and hoped for.
The standards are the same across all of it: CHAS, SafeContractor, Constructionline Gold, ISO 9001, ISO 14001 and ISO 45001, and registration under NHSS 7 where the work touches the public highway.
What to ask for in a quote.
- The method, stated by surface and contaminant, not just "jet wash".
- Whether hot or cold water is being used, and why.
- How the wash water will be contained and lawfully disposed of, and what consent that relies on.
- What will lighten rather than disappear.
- Whether existing markings, coatings and sealants have been accounted for.
- The phasing and working hours, and what access you keep.
- Whether this is a one-off or the first visit of a maintenance programme, and what the interval should be.
If new marking or coating is planned, tell the contractor at the point of the clean rather than afterwards. The two jobs are specified differently when they are planned together, and the result lasts longer for it.
