Sodium Hypochlorite vs DDAC: Choosing the Right Softwashing Chemistry

Mark Cave

A customer rings you a fortnight after a roof treatment and says, "You just sprayed water on my house." I've seen that call happen, and nine times out of ten the chemistry wasn't the problem. The expectation was.

Mark Cave

I'm Mark Cave from SoftWash UK, and today is a coaching session on one decision that shapes your results, your reputation and your income. Sodium hypochlorite, or a slow acting biocide based on DDAC. Which one, and when?

Mark Cave

Start with sodium hypochlorite. It's an oxidising agent. SoftWash UK's own technical guidance describes it as breaking down biological contamination at a cellular level, rather than just bleaching the pigment. That matters, because plenty of people think it's only a colour changer. It isn't. It needs deliberate dwell time to do its work, and on vertical surfaces you'll usually pair it with a bleach stable surfactant like Clever Wash, so it clings instead of running straight off.

Mark Cave

Now the catch. Once you've rinsed it off thoroughly, there's no residual protection left. None. Airborne spores land, and as soon as moisture and shade come back, they colonise again. So SH gives you the dramatic reset, but it doesn't give you a barrier. Customers don't always like hearing that part.

Mark Cave

DDAC is a different animal. Soft Wash Pro 50 is a 50 percent DDAC concentrate, HSE number 10245. It's a non oxidising biocide. Typical guide dilutions are one percent, which is fifty to one, for maintenance or lighter contamination, and two percent, twenty five to one, for heavier first time cleans. Allow roughly four to five square metres per litre of diluted solution, depending on porosity and contamination.

Mark Cave

It's designed to stay on the surface and work gradually, over weeks or even months. Rainfall and weathering do the rest, washing away the decomposing growth. And this connects to a recent episode on why rinsing is a chemical process, not just tidying up. With sodium hypochlorite, you rinse thoroughly to terminate the reaction, otherwise you risk crystal spalling. With a residual biocide, you do the opposite. You apply and leave it, because the weather is part of the process. Mix those two habits up and you'll get poor results either way.

Mark Cave

Let's talk surfaces, because that's where decisions get expensive. Tarmac first. Sodium hypochlorite can oxidise and bleach bitumen, and over time degrade it. DDAC is the strongly preferred choice for moss and algae on tarmac, because you avoid the oxidiser damage.

Mark Cave

Roofs. If there's a thick moss mat, scrape it off physically first. Chemistry doesn't remove bulk. And be clear on this, Soft Wash Pro 50 must not be described or sold as a moss killer. It's a biocide treatment, applied after heavy deposits are removed. Heavy pressure washing can damage tile coatings, so when the customer doesn't need an instant cosmetic reset, a low disturbance apply and leave treatment is often the sensible, kinder option.

Mark Cave

Modern render, like K Rend or monocouche, is different again. If the customer wants it looking right this week, you'll usually need SH to knock back those red Trentepohlia or green biofilms. Then you follow with routine biocide maintenance. Same house, two chemicals, one plan.

Mark Cave

That's the hybrid workflow, and it's where the business sense is. Do the deep clean with SH, rinse it thoroughly, let the surface dry down, then apply the DDAC. You've given the customer an instant result and a preventive barrier, and you've turned a one off job into annual maintenance. That's recurring revenue, built on knowledge rather than discounting.

Mark Cave

Two warnings. First, write your expectations down. If you apply a biocide and say nothing about weeks or months, you've set yourself up for the water spray complaint. Photos, a short written note, a follow up. Second, and I can't stress this enough, never mix sodium hypochlorite with a quaternary biocide or with acids in the same tank. They're incompatible, they neutralise the active ingredients, and the reactions can be hazardous. Separate containers, flush your lines, label everything. And always read the label and safety data sheet, and do a patch test.

Mark Cave

Podcasts like this are a good start, but choosing chemistry, setting up equipment, handling COSHH and pricing a maintenance plan properly takes deeper understanding. That's what the SoftWash UK CPD Certified Softwash Training Course is built for. It's online, you learn at your own pace, and it comes from years of real world experience. Finish it and you can become an Approved Softwash Applicator, get a directory listing and join the National Association of Softwash community. Have a look at softwashing.uk.

Mark Cave

Here's a challenge before your next quote. Ask yourself, does this customer need a reset, a barrier, or both? Get that right and the phone calls get a lot friendlier. Take care, and I'll speak to you again soon.