Why do marine-grade aluminium gutters have corrosion holes?

[aussiblue]

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-met... ), 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.

[Noyade]

Morning! @aussiblue 

"Does anyone have idea of the cause?"

I have nothing to offer, sorry, I thought aluminium would pretty much last 'forever' outside? Some of my gal guttering from 1947 is still going strong. My older brother is a metallurgist and lately working in aluminium refineries (he designs them) around the world - I will ask him and direct him to this site. Cheers!

[MitchellMc]

Hi @aussiblue,

My first point of investigation is the evaporative cooler, which appears to be the biggest anomaly here. Typing "Is evaporative air conditioner runoff corrosive?" into google leads to quite a few results. I'll direct you to this article from the WA Gov. "Discharge of waste - Due to the corrosive nature of the wastewater it must not discharge onto roofs or into gutters and downpipes.". After further investigation, the discharge water appears to have a higher than usual salt content as it's at a concentrated level from the evaporated water. This wastewater purges the high concentration of minerals and salt from the system. The wastewater from an evaporative cooler should not be mistaken as the same from a split-system air conditioner. The water from a split system is purely condensed moisture from the air on the cooling fins and contains no concentrated salt levels.

If the corroded guttering appears to be mainly around the area where the evaporative cooler runoff enters it and downstream of the point, I'd say it's highly likely that this is the cause of your issues. The evaporative cooler wastewater needs to be directed to ground level and discharged there. 

The lead flashing could also, but to a lesser degree, be contributing to the corrosion. I can certainly recommend the Deks 150 - 300mm Red Silicone Dektite Premium Roof Flashing as a suitable replacement.

I'm not currently aware of any aluminium guttering suppliers. Have you considered replacing that section with PVC guttering?

Please let me know if you have any questions.

Mitchell

[Noyade]

Afternoon @aussiblue 

I think you can 'un-tick' me as most helpful - probably most un-helpful! 🤔

I spoke briefly with my metallurgist brother (and showed him this link) - who possibly didn't see @MitchellMc 's post above, cause he pretty much said what Mitchell has said - galvanic reactions/corrosion - which I know little about.

And it's not what you want to hear - but he wonders what the quality of the marine aluminium is/was they gave you.

But he promises to look further into it for you.

Cheers!

Graeme

[aussiblue]

Thanks the evap system is well upstream but I guess it has to still be a considered a suspect. A roof and gutter level inspection later today should confirm all refute that but for the reasons that follow, but I am not yet ready to call it "solved".

The Tech note you pointed to was nonetheless very interesting.  When the evap system was originally installed it had a drain line of rigid PVC pipe that traveled through my ceiling space in a very circuitous roller coaster route  to the ground; this started leaking in a number of places.  Because the water obviously didn't drain through the parts that took uphill U turns the longest section at the base of the unit  about 6 meters long filled with water and became so heavy it pulled out of the base of that U joint at each end and leaked again so was then totally removed and replaced with one that discharges onto the roof..  However,  at the same time the continuous water discharge rate was increased considerably to (well hopefully) counter the risk of salinity; based on advice in Larry Galpin's  "Easy Cooler Care" Book (this https://www.goodreads.com/book/show/58499.Easy_Cooler_Care). It has two discharge tubes from two  drain funnels with all plugs in place (these https://www.gamato.com.au/product/breezair-braemar-bleed-tray-for-ea-units/ ) on each side  where a single one on one side only with some plugs out is the standard method. The drain tubes run continuously while the unit is in use and the increased discharge is certainly not very water conservation friendly and doubtless does not help my water bill (but I convince myself it's offset by not having a pool or garden reticulation). There is also no salt staining on the roof that I see with other people's systems that have drains with lower flow rates draining onto their roofs into the gutters. It also stops salts accumulating in the Aspen pads so they last longer and work more effectively. 

I have already bought an external drain to run down the roof onto the ground so now I have an added incentive to fit it ASAP. 

Based on the advice in that Galpin book, more than 10 years ago I also imported from the US  and fitted a large PVC safety tray so the Department of Commerce's Tech Note's comment about safe trays not being fitted to evap coolers does not apply in my case. Safety trays  are apparently fitted standard with most "swamp coolers" in the US and are readily available online from the US.  Any water that drains into it would flow through a very visible 1"  transparent PVC tube to the ground - there has been none so far and I annually check the tray and ensure the tube is not blocked. 

The dodgy people who fitted the evap unit originally in the 80's also stuffed up the roof flashing so my ceiling flooded when it rained and I had to replace half my family room ceiling. The installers made other major stuff ups like cutting through a roof rafter (had to be repaired with steel plates) and using a non IP rated electrical junction box inside the cooler (since replaced with an IP 66 one). About 10 years ago before replacing the ceilings, I pulled the whole system out and reinstalled it correctly and in a different place and then fixed all the consequential damage and installation  stuff ups and rust proof coated all the steel parts including the inside of the dropper.  In any event, since then I am more than somewhat paranoid about leaks, potential ceiling damage and other problems that evap units can cause,  As an aside, I also cover the cooler with a hurricane proof tear resistant cover in winter that I also import from the US; although they do eventually wear thin, they last much longer than the PVC ones sold here; another tip from Larry's book.

I will investigate the PVC gutter option but I am unsure if there is compatible profile available and I don't want to have to replace the complete gutter system again. The fact that the suppliers made a point of saying the guarantee on this guttering applied in salt affected coastal  areas (see the video) and stating that the "marine grade" aluminum it would not be damaged by discharges from evap systems is of no help to me now of course.

[aussiblue]

Thanks.  I also wonder about what grade marine grade aluminium, if any,  was used. I think my micrometer tests some years ago also indicated about it thickness compared to colorbond didn't live up to the claims made of it being twice as thick.

[aussiblue]

My existing gutter's profile is what is known variously as colonial, S Profile, Classical, O.G or Ogee. So they are not compatible with the Ikon PVC profile gutters sold by Bunnings.  I have found there are companies in Sydney and Melbourne that still sell the same type of continuous aluminium gutters I have (noticeably without any 25 year life claims or similar length warranty periods ) so perhaps I can get them to ship me a section to use for repairs.  A search using the string "continuous aluminium guttering" finds them. The company that used to install them in Perth (not the supplier just a company the supplier recommended for instillation)  also still in business so I will also call them tomorrow see if the have any repair pieces on hand. There are compatible colorbond steel profiles available so if all else fails I might cautiously test the continuous aluminium guttering maker's claim that you can mix these two types although mixing steel and aluminium to me seems doomed to failure. t I haven't been well enough to get on the roof today (feeling a little faint as recovering from minor surgery and I don't want to put my roofer's helmet and fall arrest harness system to the ultimate test. But I will try tomorrow. Some pics of the damage below:

[MitchellMc]

Just to clarify, @aussiblue, when you say the evaporative cooler is well upstream, are you saying that it is on the lower side and any runoff doesn't flow over the damaged area? That would suggest that it's likely not caused by the evap then. I would expect the damage to be directly where the runoff enters the gutter and then along it towards the downpipe.

Please do take care when you get up on the roof and put it off until you feel better. You might also like to read through this helpful guide on How to use ladders safely.

Mitchell

[aussiblue]

No; the water does flow over it.  A less than thorough  inspection on a ladder (still too dizzy to get on the roof) showed moss and weeds growing in the bottom of the corroded area, hidden from a casual view below the gutter guard, partially blocking the gutter, so I think that is the cause.  It seems I should have used my Karcher on the gutters in the middle of summer too.  But It does also suggest just regular water flow and accumulation of tile dust and dead moss that the weed grew on, rather than salinity, is the cause (I doubt moss and weeds would survive in salty water). It's probably also why the corrosion is half way down rather than at the base of the gutter.  Ironically, despite my concerns about moss appearing on the tiles, I chose not to apply any moss killing chemicals to the roof because of concerns about reactions with the aluminium guttering.

[MitchellMc]

Thanks for clarifying, @aussiblue.

I urge you to think about your safety and not get on a ladder whilst suffering any dizziness. This issue has been around for several months, so it doesn't require immediate attention. As someone who has always been very confident on a ladder and has never had any issues, I recently fell from a ladder at a considerable height and came very close to breaking both my legs. My father-in-law (an experienced tradesperson) recently fell from a moderate height and severely broke his ankle. Accidents can happen no matter how confident you are, and your safety is my number one concern.

Mitchell