Beyond the Bleach: The Science and Standards of Softwashing

Mark Cave

Let's clear up a myth. Plenty of people think softwashing is buying a pump, a drum of bleach, and blasting walls. If that's your picture of the job, this episode is for you.

Mark Cave

I'm Mark Cave from SoftWash UK. Last time I walked through the five pillars of professional softwashing: chemistry, surface identification, delivery, safety, and the business side. Today I want to show you how deep those pillars go. When we mapped out every practical scenario you can meet on site, we ended up with a curriculum of 240 topics. Each one is a decision you can get right or wrong.

Mark Cave

Start with the bleach itself. Sodium hypochlorite works by biological oxidation. It breaks down the living film of algae, mould and lichen. Fresh stock is typically 14 to 15 percent, but heat, sunlight and poor storage drag that down fast. So a drum that's been sat in a hot van isn't the drum you bought.

Mark Cave

And here's the part beginners miss. You never spray stock strength. The final strength on the surface is typically 1 to 3 percent for general render and biological growth, and up to 4 to 6 percent for heavy organic contamination. Stronger isn't better. Stronger wastes money, scorches the customer's garden, and risks damaging the surface you're being paid to clean.

Mark Cave

Then there's surfactant. A bleach stable one, like Clever Wash, goes in at 200 to 1, which is five millilitres per litre. Its job is to lower surface tension so the mix wets the surface and gets into the biofilm. It's not there to make thick foam. Foam that sits on top looks impressive and cleans very little.

Mark Cave

Next, residual biocides. DDAC and BAC are quaternary ammonium compounds. They work slowly and leave protection behind. They matter on porous roofs, and on tarmac, where sodium hypochlorite attacks the bitumen binder. But you have to set expectations. Dead lichen and moss weather away over weeks or months. They don't vanish on the day.

Mark Cave

And then the rule that has to be burned into your head. Oxalic acid is what you need for rust weeping, mineral staining and lead run off from flashing. But you never mix acids with sodium hypochlorite. Never. It releases chlorine gas immediately. That's one line in a sentence, but it's a whole discipline of segregation, labelling and mixing order.

Mark Cave

Now the surfaces. Take roof tiles. Major manufacturers are on record warning against pressure washing. Marley says high powered jet washes can damage the tile surface and reduce its life. Wienerberger, who make Sandtoft tiles, warn that jet washers can strip colour and finish. Forticrete says power washing removes fines from concrete tiles and would invalidate the guarantee. Tudor Roof Tiles say pressure washing should never be used on their clay tiles. The Roof Tile Association and the NFRC both advise against violent methods like power washing.

Mark Cave

So the professional standard is two stages. First, scrape the bulk moss by hand with specialist profiled blades. Then apply a biocide at low pressure. And when the customer says you've bleached their roof, you explain that cleaning often reveals existing weathering and lost factory coatings. The dirt was hiding it. You didn't cause it.

Mark Cave

Render is the same story. Monocouche behaves differently from silicone thin coat on an EWI system. Old painted render can hide chalking or a failing binder. Limestone and travertine will dissolve under acidic cleaners. Indian sandstone with black spot needs controlled dwell times. Tarmac binder breaks down under solvents and high pressure. Two surfaces that look similar can react completely differently, and that's why test patches matter. Use them as due diligence, and feather the edges so you don't leave a bright halo on the wall.

Mark Cave

Delivery is where many people fool themselves. It's flow rate and dwell time that clean a surface, not PSI. And if you run an inline proportioner, such as a Dosatron or a Clever Injector system, remember that backpressure and hose friction can make the real mix drift away from what the dial says. So test the strength at the nozzle. Don't trust the dial on its own.

Mark Cave

Then your duty to the site. Pre wet soil and planting to saturation so roots can't take up chemical run off. Find out whether a drain is surface water or foul sewer before you spray a drop. Where run off can't safely enter a drain, use drain blocks or collect it. And do your COSHH responsibilities properly, with a RAMS written for that site, not a generic tick box sheet.

Mark Cave

And the business. A quote that only counts spray time will lose you money. Price in the survey, the access, whether that's poles, towers or a MEWP, the masking, pre wetting, dwell, rinsing, and a margin for weather. Then you've got the customer who wants instant results. Part of your job is explaining why a slow clean biocide can be the better choice on certain materials.

Mark Cave

Podcasts and articles are a great start, and the Knowledge Hub at softwashing.uk is free. But no one can absorb 240 topics from a van seat. That's why we built the SoftWash UK CPD Certified Softwash Training Course. It covers chemistry, health and safety, surface science and commercial setup, online, at your own pace, and it comes from years of real work on real jobs.

Mark Cave

One more thing that surprises people. Exterior cleaning falls under Building Repair and Maintenance with CITB, so eligible registered employers can claim up to 70 percent grant funding. Check your own eligibility with CITB first. And once you've completed the certification, you can become an Approved Softwash Applicator, get a listing in the directory, and join the National Association of Softwash community, so you're not working it all out alone.

Mark Cave

Here's my challenge to you. Pick the last job you did and ask yourself honestly: what was the final strength on the surface, what was the substrate, and where did the run off go? If any of those answers was a guess, you've found your next thing to learn. Head to softwashing.uk, look at the training, and let's raise the standard together. Take care, and I'll speak to you in the next one.