Batch Mixing vs Proportioning Systems in Softwashing

Mark Cave

When a render clean goes wrong, what's the first thing most contractors say? The bleach must have been weak. Or, the bleach must have been too strong. Either way, they blame the chemical. In my experience, that's rarely where the problem sits. The problem is delivery. It's how that chemical got from the drum to the wall, and whether you actually knew what strength you were putting on.

Mark Cave

I'm Mark Cave from SoftWash UK, and today we're comparing batch mixing with proportioning systems. A while back I said new contractors should master batch mixing in calibrated containers first, because it forces you to learn the dilution maths. Today is the next step. What are your options, what do they cost you, and when does it make sense to move on?

Mark Cave

Let's start with why this matters. When operators eyeball a drum, or top up a half empty tank on site, concentration errors can swing by up to 40 percent. Think about that. Too weak, and the algae survives, the render dries patchy, and you're back on site unpaid. Too strong, and you're wasting expensive chemical, scorching planting and risking streaks on the surface. Same chemical, same drum. Completely different outcome.

Mark Cave

So here's how proper batch mixing works. You measure your water first. Then you add your concentrate, say sodium hypochlorite at 14 to 15 percent, or a biocide. Then the bleach compatible surfactant goes in last. Clever Wash, for example, runs at 200 to 1, which is 5 millilitres per litre. And the maths is simple. Target strength, divided by stock strength, multiplied by your final volume. Three percent from a 15 percent stock, making 20 litres, is 4 litres of hypochlorite and 16 litres of water. Know your stock strength, because drums vary and hypochlorite weakens with age.

Mark Cave

Batch mixing comes in two main forms. First, the portable trolley. That's a dedicated 12 volt battery trolley, usually 25 to 50 litres, with Viton seals. It's brilliant for rear gardens, courtyards and domestic bungalows. Why? Because dragging a long hose run through a house or round a tight property costs you flow through friction, and causes disruption. The outlay is low and it's very agile. The trade off is capacity. You'll be refilling a lot.

Mark Cave

The second is the static van tank. We're talking 100 to 300 litres or more, paired with a 12 volt diaphragm pump, something like a Remco or a Flojet. The big advantage is honesty. If you've calculated that tank accurately from scratch, the chemistry in it cannot lie, regardless of hose length. But think about the weight. One litre of water is one kilo. A 200 litre tank adds 200 kilos of liquid, plus the tank, to your payload. Add sloshing on corners, hypochlorite breaking down in a hot van, leftover mix going to waste when a job finishes early, and the downtime when it runs dry halfway across an elevation.

Mark Cave

And that brings me to the top up trap. Picture it. You start with a full tank. By lunchtime it's half gone. You grab a container of hypochlorite, tip in what feels about right, top up with the hose, and carry on. You haven't drained it. You haven't recalculated. Now the strength is a guess, and it's probably higher. The top of the wall looks brilliant, the lower section is streaked, and the landscaping is paying for it. That's how a decent morning turns into an expensive callback.

Mark Cave

Now, proportioning. Let's go through the options honestly. First, the downstream venturi injector. These are inexpensive, and they pull chemical in after a pressure washer pump. They're fine for light detergents. But for controlled softwashing they're inaccurate. Draw rates shift with hose length, elevation, tip size and any drop in water pressure. Maximum draw ratios typically hover below 10 to 20 percent, so high strength render or roof applications simply aren't possible. Change your nozzle and your strength changes with it.

Mark Cave

Next, the proportioning manifold. That's a three way valve block metering water, neat hypochlorite and surfactant into a 12 volt pump. It removes the hold tank, so no payload problem. But backpressure, line friction, think 50 metres of half inch hose, and the thickness of the surfactant can all make the real output drift away from the numbers on the dial.

Mark Cave

Then there's the water powered hydraulic injector. That's your Dosatron, or the Clever Injector. No electricity. The water flow drives an internal piston, which draws concentrate straight from the original container into the water line at a percentage you set. It mixes on demand. Close the trigger, and the draw stops instantly. You're not carrying hundreds of litres of corrosive mixed liquid. It can cut chemical waste by up to 25 percent, and it makes COSHH records simpler, because you're recording a setting, not a guess. The downsides are real, though. The entry price is higher, roughly £500 to £1,600 and above. You need adequate water supply pressure. And you must calibrate it routinely.

Mark Cave

That calibration point is critical. Turning the dial to three percent does not mean three percent lands on the wall. So do the 60 second bucket test. Run your chemical intake from a graduated measuring container, with your hose at its real working length, for 60 seconds. Measure how many millilitres were drawn against the total water volume. If it's off, adjust and test again. It takes a minute, and it happens before any chemical touches a customer's building.

Mark Cave

So which system should you choose? Match it to your business stage. Start with a simple batch trolley or tank you fully understand. Learn the dilution maths, learn site control. Then scale into calibrated Dosatron setups when commercial speed and repeatability matter. And remember, commercial work, facilities management contracts and high ticket domestic jobs need proper RAMS, site specific COSHH assessments, pre wetting of vegetation and drainage control. Equipment doesn't replace any of that. Knowledge comes before products, every time.

Mark Cave

Podcasts like this are a great starting point, but if you're serious about offering softwashing professionally, the SoftWash UK CPD Certified Softwash Training Course goes much deeper. Delivery systems, calibration, surface science, safety, all built from years of real world experience, and you learn online at your own pace. Completing it opens the door to becoming an Approved Softwash Applicator, with a directory listing and a place in the National Association of Softwash community. Eligible CITB registered employers can also claim up to 70 percent grant funding under Building Repair and Maintenance. Have a look at softwashing.uk.

Mark Cave

Here's my challenge. On your next job, run that 60 second bucket test, or if you batch mix, recalculate instead of topping up by eye. Write down what you find. You might be surprised. Thanks for listening, and I'll catch you in the next one.