Protecting Architectural Metals During Softwashing

Mark Cave

Picture a sunny afternoon. You've softwashed a rendered gable, it looks fantastic, and you're packing up. Then the customer points at the bifold door frame and says, "What's that milky streak?" You wipe it. It doesn't wipe. That's etched aluminium, and it's not coming back.

Mark Cave

Hello, I'm Mark Cave from SoftWash UK, and today we're talking about cleaning around metals without causing reactions. Aluminium, lead, copper, zinc, stainless steel, and painted or powder coated metalwork. Most of us survey the wall or the roof. Far fewer of us survey the metal sitting on it.

Mark Cave

Let's start with why metals are vulnerable. Sodium hypochlorite, SH, is a powerful oxidiser. That's exactly why it kills algae so well. But oxidising is a chemical reaction, and when SH lands on metal, the metal reacts too. You can get pitting, discolouration and staining, and it can start straight away.

Mark Cave

Each metal reacts in its own way, so let's go through them. Lead flashing turns dark brown, what we call scorched, because of lead dioxide forming on the surface. If you listened to our earlier episode on pink UPVC and scorched lead, you'll know that reaction. Today is about stopping it before it starts.

Mark Cave

Bare aluminium, so window trims, copings and bifold frames, oxidises quickly. It etches, and you get those milky white streaks or a pitted, hazy look. That's the one you can't simply wipe away.

Mark Cave

Zinc and galvanised steel, so gutters, downpipes and architectural cladding, react strongly to chlorine and to acidic cleaners. You can strip the protective layer and end up with mottled black or white oxidation. Copper and brass, think downspouts, bell pushes and exterior lighting, tarnish quickly to a greenish black patina when they meet strong oxidisers.

Mark Cave

And then painted and powder coated metal. If that coating is aged, thin, or already weakened by UV, hypochlorite or even a surfactant can cause dulling, chalking, or edge lifting. A good coating usually copes. A tired one often doesn't. And from the ground, you can't always tell which you've got.

Mark Cave

So, before you touch the chemical rig, do a metal survey. Walk the whole elevation and list every piece of architectural metal. Window sills. Bifold door tracks. Flashings. Metal soil pipes and vents. Outdoor lights. Copper eaves. Aluminium composite cladding. If it's metal, it goes on the list.

Mark Cave

Then, and this one gets overlooked, follow the runoff path. Ask yourself where the chemical goes after it leaves the wall or roof. A roof wash can run down onto a lead valley, a zinc box gutter or a copper bay canopy below. You might never have sprayed those directly, but the runoff gets there anyway. That's one of the most common ways people cause damage without realising.

Mark Cave

Now the protection protocol. First, wet the metal with clean water before you apply anything. Saturate it. That water acts as a sacrificial barrier. Any drift or overspray that lands on a wet surface is diluted straight away, instead of sitting on bare metal at full strength.

Mark Cave

Second, mask the high value or unprotected pieces. Raw aluminium trims, delicate zinc capping, an untreated copper lantern. Tape them and cover them with sheeting. It takes a few minutes, and it's far cheaper than a replacement part and an awkward phone call.

Mark Cave

Third, keep a rinse line active. When you're spraying walls or roofs next to metal, have somebody on the ground continuously wetting and flushing the metalwork. If you're on your own, plan your sequence so you can rinse as you go. The aim is simple: the chemical never gets time to dwell on the metal.

Mark Cave

And fourth, rinse straight after application. Never let softwash chemical dry on metal. Drying concentrates it, and on a powder coated frame in direct sunlight, that quick evaporation can leave permanent chemical burn marks. So think about the sun on the elevation, not just the wind.

Mark Cave

Let's cover a few mistakes I see contractors make. One is treating rust or efflorescence with acids, such as oxalic or brick acid, close to galvanised steel or bare aluminium. Acids and those metals don't get on. The other is mixing acids anywhere near SH. That's a toxic chlorine gas hazard, and it's a serious one. Keep them separate, in storage, in mixing and on the wall.

Mark Cave

Then there's a business point. Before you quote or spray, photograph what's already there. Existing oxidation on aluminium. Chalking on a powder coat. Old runoff corrosion under a lead flashing. If a customer later says you caused it, dated photos from before you started are the best protection you've got. And if the metal is already in poor condition, tell the customer, in writing, before the work starts.

Mark Cave

Here's the bigger message. Most of these problems aren't product failures. They come from not knowing what you're looking at, or not having a workflow. Knowledge comes before chemicals. Understand the surface, understand the reaction, and the damage mostly prevents itself.

Mark Cave

Podcasts like this are a good start. But if you're serious about offering softwashing professionally, the CPD Certified Softwash Training Course at softwashing.uk goes much deeper into surface identification, chemical selection, application, safety and pricing. It's online, so you learn at your own pace. It was built from real industry experience to help contractors avoid expensive mistakes. And completing it gives you the chance to become an Approved Softwash Applicator, with a directory listing, and to join the National Association of Softwash community.

Mark Cave

So here's your challenge for the next job. Before you mix a drop of chemical, walk the elevation and count the metals. Write the list down. Photograph them. Then plan how each one gets wetted, covered and rinsed. Do that every time and you'll avoid most of the reactions we've talked about today.

Mark Cave

Thanks for listening, and I'll catch you in the next one.