In Autumn 2015 we replaced all my gutters around my house with marine grade aluminum gutters. Today I noticed white corrosion marks on the outside of the gutter and when i touched them (well pressed hard on them with my finger) they turned into round 0.22 bullet sized holes. These gutters were meant to last 25 years and outlive me but they are not yet 8 years old. I'll post some pics tomorrow when it daylight and easier to do so. From my evening inspection it (hopefully) seems confined to a section of just less than 3 meters (or just 0.5 of a meter greater than the spare guttering I have on hand).
Does anyone have idea of the cause? I clean the gutters each year before winter with my Karcher pressure washer and it's drain cleaning attachment so I think my gutters are well cared for. The only two things that set this section of gutter apart are that a) its below my roof mounted evaporative air conditioner and collects it's runoff about 10 meters upstream (the runoff from the overflow is now leaking out my holey gutters) and b) it's almost immediately below but about half a meter downstream not upstream of a square of lead flashing that surround the soil vent pipe for the kitchen sink drain. A bit of "googling"suggest that run off from lead flashing may cause galvanic corrosion of both aluminum and colorbond gutters (see https://gartalk.garlandco.com/2012/09/19/understanding-galvanic-corrosion-and-how-to-avoid-it-in-metal-roofing/ ), So is this the likely cause?
I will have to check in daylight but perhaps the fancy flashing around the dropper on the roof is also lead. Just found the brochure and it a DEKS SDA55 rubber and aluminium product (this: https://deks.com.au/product/dektite-evap-blk-550x550-1040x1290mm-gry/ ) so that's not the cause.
I see that the business I purchased from closed up shop in August 2021. So I guess the claimed 25 year guarantee is out the window. I guess if a rooftop inspection tomorrow confirms the corrosion is confined to this one section I will have to cut it out and fit a new section of aluminium guttering. Now that business is no longer operating is there somewhere else I can buy a replacements section. Obviously I cannot use steel or colorbond guttering as it will cause corrosion if fitted between aluminium guttering.
The Weatherflash fully annealed, 99 percent pure, uncoated aluminium flashing would seem best for replacing the existing lead flashing square but Bunnings don't seem to sell it in 450 mm squares like they do the lead flashing; so is there another alternative? OK checking out my Decktite evap flashing suggests that something like this from Bunnings may be the way to go https://www.bunnings.com.au/deks-150-300mm-red-silicone-dektite-premium-roof-flashing_p4829521.
