Why Washing Up Liquid Destroys Your Softwash Mix

Mark Cave

Two hundred and fifty millilitres of washing up liquid. That's what one contractor squeezed into a fifty litre tank of sodium hypochlorite, and it cost him half a day on site. He rang me in a proper panic, because he'd mixed a fresh five percent batch, put it on a commercial elevation covered in heavy green algae, and nothing was lifting.

Mark Cave

I'm Mark Cave from SoftWash UK, and today I want to talk about that van side shortcut. You've probably seen it. Somebody reaches into the van, grabs a bottle from the supermarket, and gives the tank a big squirt. The thinking is, detergent is detergent. A bit of foam, a nicer smell, better cling. It seems harmless.

Mark Cave

It isn't. Sodium hypochlorite is a powerful oxidiser, and it isn't picky about what it attacks. It goes after anything organic it can find. Household washing up liquid is full of exactly that: oils, colourings, and fragrances, often citrus based ones, and none of them are made to survive in bleach.

Mark Cave

So the moment that soap hits the tank, the chlorine starts working on the perfume and the lemon scent instead of saving itself for the algae on your wall. It's a bit like paying a gang to clear a roof and watching them spend the morning on the kettle. The power gets used up in the wrong place.

Mark Cave

Over the following hours, that strong mix breaks down towards salt and water. You think you're spraying a three or five percent solution. In reality, you may be spraying slightly salty, soapy water. That's what happened to my caller. When I looked in his tank there was a thick layer of green bubbles on top, and I had to explain that his three quid bottle of dish soap had wrecked about fifty quid of chemical before he'd even pulled the trigger on the lance.

Mark Cave

And that's only half of it. Domestic detergents are built for plates, not for mineral surfaces outdoors. Some contain conditioning agents and heavy foaming surfactants, and if they're not fully rinsed off, they leave a sticky film. On monocouche render, silicone render, or UPVC fascias and soffits, that film becomes a dirt magnet. Traffic film and dust cling to it, and within weeks you get streaking. Then comes the phone call from the customer, and it's your name on the job.

Mark Cave

If you listened to our earlier episode, The Science of Surfactants, and the lollipop molecule, this is where it connects. A proper surfactant has a head and a tail, and it's engineered to do a specific job in a specific environment. Washing up liquid has a surfactant in it too, but it comes bundled with all the extras that bleach destroys, and the leftovers that stay behind.

Mark Cave

Now, the big myth in our trade is foam. Plenty of contractors believe that if the wall isn't covered in shaving cream, the chemical isn't working. I'd say that's wrong. Thick foam can trap air, it can sit on top of the growth rather than getting into it, and on a vertical render wall it often just slides off under its own weight. It looks fantastic on social media. It doesn't mean a deeper clean.

Mark Cave

What you actually want is wetting. Water naturally beads up and sits on a surface. A good surfactant lowers that surface tension, so the droplet flattens out and the sodium hypochlorite can get into porous render, into the fissures of a roof tile, and down to the spores of algae, lichen and black spot. That penetration is what gives the longer lasting result.

Mark Cave

So what does doing it properly look like? A bleach compatible surfactant like Clever Wash is designed to be used with sodium hypochlorite, and the guide ratio is two hundred to one. In a batch mix, that's five millilitres per litre of softwash recipe. Fifty litres, two hundred and fifty millilitres. Funny enough, that's the same quantity my caller poured in as dish soap, except this one is designed for the job.

Mark Cave

If you're running a proportioning system, such as the Clever Injector Dosatron, the guide is five hundred millilitres per twenty five litre drum of sodium hypochlorite. So a five litre container treats ten drums. That's the difference. One is a measured dose, the other is a haphazard squirt. Even then, you test a small area first, read the label and the safety data sheet, and keep runoff out of the drains.

Mark Cave

Here's the practical takeaway. Stop using household products in your mix. Measure everything. Write down what went into the tank. And if a job underperforms, check your chemistry before you blame the wall. Choosing the right chemical isn't a cost issue, it's trade competence.

Mark Cave

Podcasts like this are a good start, but being a professional means understanding chemical selection, application, surfaces, safety and pricing properly. That's why we built the CPD Certified Softwash Training Course at SoftWash UK. It's an online course you take at your own pace, and when you complete it you can become an Approved Softwash Applicator, get listed in the directory, and join the National Association of Softwash community. Have a look at softwashing.uk.

Mark Cave

So here's a challenge. Go and look in your van this week. If there's a bottle of washing up liquid in there near your chemicals, ask yourself why. Take care, and I'll speak to you again soon.