Why Foam Isn’t Cleaning Your Render

Mark Cave

Picture a rendered wall with three inches of shaving foam sliding down it. It looks brilliant on camera. Thousands of likes. And I'd bet a drum of hypo that the algae underneath is, um, sitting there perfectly happy. So today's question is a simple one. Is thick foam actually cleaning anything?

Mark Cave

Here's the uncomfortable bit. Foam is mostly air. The figure I've always worked with is over ninety percent trapped air bubbles. So you've got a blanket of bubbles sitting between the liquid sodium hypochlorite and the wall. The, the, the chemical that's supposed to touch the biofilm is stuck up inside the lather, insulated from the surface.

Mark Cave

Now, the obvious pushback. Mark, you sell surfactant, surely foam helps? And, er, fair enough, it does a little. SoftWash UK's own article on surfactant quality puts it like this: the best surfactant is not simply the one that foams the most. Foam can help the operator see coverage. That's it. It's a visual aid for you. It's not the cleaning.

Mark Cave

Then there's the weight. Heavy, dense foam drags downhill. On vertical monocouche or silicone render, that lather slumps. It slides off in sheets. Within about two minutes your mix is in the flowerbed and the gutters instead of sitting on the wall doing its job. So you've lost your dwell time, you've wasted chemical, and you've, you've stressed the plants. All for a nice video.

Mark Cave

Now the one that really got me. I was called to look at a failed render clean. The contractor was baffled. Green algae still all over the elevation. And I asked what was in the tank. He'd mixed a car style foaming detergent in with fifteen percent sodium hypochlorite, because it made great bubbles.

Mark Cave

And the problem is, nobody had checked what was in that soap. Organic additives. Sodium hypochlorite is an oxidiser, so it attacks organic material. It, it, it doesn't care whether that's algae or a perfume in your detergent. So inside the tank, the additives were oxidised almost instantly, eating up the available chlorine before a single drop reached the wall.

Mark Cave

What went on the render was sweet smelling bubbles. Inactive. Lovely to look at. Didn't budge the algae. He re-treated it, and re-treated it, blaming the render, blaming the weather, and the real culprit was the bucket he started with. That's the trap. You can't see a dead mix. You can only see foam.

Mark Cave

So if foam isn't the job, what is? Think about a drop of water on a waxed car. It beads up, right? Render can behave the same way. Water holds itself together, that's surface tension, and on a water repellent wall your mix just sits in little beads and runs off.

Mark Cave

A proper surfactant is a wetting agent. Not a bubble machine. It breaks that surface tension so the beads flatten out into one continuous, microscopically thin sheet. And that matters because algae protect themselves with a slimy layer, a kind of shield. A thin, even sheet of solution can get into that, where beads just bounce off it.

Mark Cave

Right, so you might think, well, if a bit is good, a splash extra must be better. I hear that one constantly. And, um, no. Too much surfactant can leave a sticky film on the surface. That film can hold on to road traffic grime, and I've seen it lead to quicker regrowth. I'd flag that as my experience, not a lab result, but the logic holds up.

Mark Cave

So this is where discipline comes in. The guide rate on the Clever Wash product page is this: Clever Wash is typically used at a guide rate of 200:1. Always assess the surface, contamination level, and so on. In practice, that's five millilitres per litre of softwash mix. A hundred litre batch gets five hundred millilitres. If you're running a Clever Injector Dosatron, it's five hundred millilitres per twenty five litre drum of hypo.

Mark Cave

That's enough to see where you've been, and to get cling and wetting. Go ten times heavier and you're not cleaning better, you're, you're, you're signing up for a two hour rinse down. Measure it. Don't glug it.

Mark Cave

And that's really the dividing line between a professional and a splash and dash operator. Not the foam, not the kit. It's knowing why the chemistry behaves as it does, profiling the surface first, and getting the same result on job fifty as on job one. That's what we teach on the CPD Certified Softwash Training Course at softwashing.uk, and it's why I'd point people towards NASW membership as well, for the support once you're out on real jobs.

Mark Cave

So, back to that wall. Three inches of foam is a magic trick. A thin, even sheet of properly dosed mix is a clean. Next time you mix up, ask yourself whether you want it to look good, or work. I know which one the customer's paying for.