How NOT to cause blotches when you install your metal finish.

Every boatie will tell you the importance of having a sacrificial anode on their boat. The reason is that electrical currents passing from the boat to the water will take the path of least resistance, and as it leaves it will take a small piece of the boat with it. Hence this anode gets eaten away before the boat (or motor) is targeted.

The sacrificial anode is usually Zinc, because Zinc is a good conductor. And that’s also one of the key reasons it’s so popular to put Zinc on our roofs and walls (to act as a heat sink – dissipating heat and spreading it across the structure).

But because of Zinc’s conductivity, you have to be very careful what you put next to it. Even a lot of installers don’t understand it fully.

Take, for instance, the window frames and joins. Usually they’re Aluminium, which reacts with the Zinc. But there’s a worse offender, which is often totally overlooked…


Most sunscreens are Zinc Oxide or Titanium Dioxide based, since this is a very good reflector of UV rays. If your sunscreen’s translucent, it’s using old-school metals, and if it’s clear (as most are today) it’s using nano-technology to get a particle as much as a millionth of the size. Both react with the metals to cause discolourisation. This is not limited to direct exposure to metals, as it reacts with pigments in paint also. This is why you’ll often see handprints or smudges on car paintwork, and even on interiors (particularly arm rests, and window ledges).

So roofing installers need to take special precautions when installing metal finishes. Where possible, protective plastic films should be left in place until the job is almost completed, and gloves should be worn at all times. Installers need to be aware that if they so much as mop their brow (on a stiflingly hot Auckland day) they’ll transfer nano-particles to their tools and their materials.

So don’t be sloppy when you’re dealing with sunscreens. It would be a real shame to install shiny new guttering only to have it looking blotchy and smudged after six months. A few checks and precautions up front could save you from a costly repair bill down the road.

For well over 15 years Metal Design Solutions Ltd has pioneered advances in the architectural metal industry installing Zinc Roofing / Copper Roofing / Stainless and Aluminium Roofing and wall Cladding. Metal Design Solutions Ltd’s work is now found in and around structures across New Zealand. Check us out at