Why High Pressure Ruins Tarmac Cleaning

Mark Cave

You know, I see it happen almost every single week across the UK. A contractor gets a call to quote a driveway, they pull up on site, and they treat a tarmac driveway exactly the same way they would treat standard concrete block paving. And honestly, it is one of the most expensive mistakes you can make in this industry.

Mark Cave

I, I, I mean, if you blast tarmac with high pressure jetting, say up at two thousand five hundred plus PSI, you are not just blowing away algae and moss. You are literally stripping the flexible bitumen oil binder right out of the aggregate. That bitumen is what binds the stone together. So when you hit it with that kind of brute force, within a season or two, a four thousand pound tarmac driveway turns into loose gravel with pitted crumbling edges. You have effectively destroyed the structure of the surface.

Mark Cave

And then there is the chemical side of it, which is where so many guys get caught out. They think, well, sodium hypochlorite works on render and concrete, so why not hit the tarmac with a strong mix? But here is the reality. If you use over concentrated sodium hypochlorite, anything above a two percent active strength, or if you pour harsh solvent degreasers on it, those chemicals actively break down the asphalt oils. You get permanent grey bleaching, and even worse, structural surface softening where the tarmac turns soft underfoot on a warm day.

Mark Cave

I remember looking at a job where a cleaner had done just that, trying to rush a black spot removal job on an asphalt entry. He got the black spot off, sure, but he left giant white rings and softened the surface so badly that car tyres were digging ruts into it by mid afternoon. That turned into a massive property damage claim and a completely furious homeowner. And it all stems from treating porous tarmac like it is stone or concrete.

Mark Cave

So how do you actually clean tarmac safely and profitably without destroying the bitumen? It comes down to a proper two step low pressure strategy. First, you perform a light mechanical scraping to gently remove those thick surface moss clumps. You do not need high pressure for this. A gentle scrape gets the bulk off.

Mark Cave

Then, you follow up with a residual DDAC biocide application. We dilute that biocide between twenty five to one and fifty to one depending on the level of contamination and ambient temperature. You spray it on at low pressure, and you let the chemistry do the work. Over a period of six to twelve weeks, the weather and rain naturally rinse the dead organic matter away as the biocide self cleanses the surface.

Mark Cave

Now, you have to understand the absorption math here because tarmac is a completely different beast compared to smooth concrete. Industry guidance points out that tarmac can be surprisingly absorbent due to its structure, so expect higher product usage compared to smoother surfaces like concrete. In real terms, asphalt absorbs thirty to fifty percent more liquid than standard concrete paving. If you do not control your application volumes, you are going to get massive chemical runoff flowing straight into flowerbeds or down storm drains, which is a major compliance risk under COSHH and environmental regulations.

Mark Cave

The beautiful thing about this safe biocide method, though, is how it sets you up for recurring commercial and domestic revenue. Instead of a one off blasting job that ruins the driveway, you educate the client on a twelve to twenty four month maintenance cycle. You return every year or two for a quick preventive treatment that keeps the tarmac permanently clean without any harsh damage.

Mark Cave

If you want to master these chemical dilutions, surface identification, and safety procedures properly, check out our SoftWash UK CPD Certified training course over at softwashing.uk. Getting the technical standards right protects your business, protects your customer's property, and builds a far more profitable company in the long run. Do it right, keep the pressure off, and let the science do the heavy lifting.