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Will Zinc React Unfavorably with Aluminum

08/25/2011 10:48 AM

Greetings All,

I have been battling lichen growth on my home asphalt shingle roof (north west exposure) for three years with multiple bleach/water applications, wonder roof cleaners, and some whizz bang magic powder.

So far I have escaped with only slight cosmetic damage but it keeps coming back. I have come to the conclusion that there has to be a more effective, semi permanent solution.

NOTE - This photo is prior to the first cleaning this past spring.

After some research and discussions with locals I have elected to go with a zinc strip at or near the aluminum ridge vent the full length of the structure.

I have received contradictory advice whether I should install the zinc strip under or below the aluminum ridge vent.

My question is: Should I install the zinc strip tucked under the first course (near the ridge) of shingles or can I install the strip tucked under and in contact with the aluminum ridge vent?

I realize that a single course difference of 5" from the ridge vent may seem inconsequential but the lichen growth starts immediately past where the ridge vent ends.

My concern is a potential chemical reaction between the zinc and aluminum such as deterioration of the ridge vent or shingles, discoloration of the shingles (from rain washing down), spontaneous combustion, or any other unfavorable reactions

I am located in the east central plains area so salt spray/salt water will not come into play.

Thanks in advance for your comments and suggestions!

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#1

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 11:19 AM

From: metaloffcuts.co.uk/shop/sheet-metal/​sheet-metal-zinc.html

Zinc is compatible with aluminium and stainless steel and can be included in building features. Zinc sheet metal is traditionally used to create distinctive long lasting architectural building features and finials.
Zinc is also used in interior design to create rustic charm and character in features such as countertops, tabletops and splashbacks.

Good luck. It looks quaint.

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#2

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 11:32 AM

..........OK so far, only from an electrochemistry perspective the zinc is more electropositive than the aluminium, therefore the aluminium will corrode preferentially over time. So they need to be electrically isolated from each other when used in the same structure for the best results. Otherwise there will be tears....(this type: ).....

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#3

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 11:36 AM

No worries. Zinc strips to control the moss will be fine. Most houses use aluminum gutters and in my case this hasn't affected them for over 30 years.

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#4

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 11:58 AM

Lyn/PW/Pete,

Thanks for the replies.

I am thinking I will butt the zinc up under the aluminum ridge vent, as far as isolation between the two, just to be safe, I can isolate with roof felt double folded.

I am only tucking under about an inch so no major inconvenience with that.

Now that we have that resolved, can I interest one or all of you to come over and install this? As I have gotten older, heights and falls have become less and less appealing to me

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#5

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 12:09 PM

KJK, when this roof is finally ready to be replaced, there are a number of premium shingles that have copper oxide granules mixed in with the gravel that is pretty good at preventing fungal growth. you might look into using those shingles when the time comes to replace them. also, most ridge vents, particularly those like are used down here on the gulf coast that have to withstand hurricane force winds are plastic these days.very few are aluminum anymore. The Elk Prestique ones I used when I replaced my roof oh, I guess 8-9 years or so ago have done a pretty good job preventing fungal growth.

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#6
In reply to #5

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 12:19 PM

Rorschach,

Thanks for the tips. I will definitely look into the copper oxide granule shingles and the plastic ridge vents when replacement time comes!

Thanks again - KJK

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#17
In reply to #5

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 9:41 PM

If you were to have a ridge vent bent up out of copper sheet instead of aluminum (or plastic) you'd probably NEVER have any lichen ever again.... but it wouldn't be cheap.

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#20
In reply to #5

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 4:42 AM

Paint the aluminium with copper sulphate solution. This will cause the copper to replace some aluminium, and give it a coppery sheen. With any luck, the copper will leach down on to the roof and do its work. Obviously you need to redo the application from time to time. Just suddenly occurred to me, thinking about the miners throwing aluminium cans into a copper tailings dam, and making a few bob on the side selling the resultant copper.

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#7

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 1:46 PM

I have had good results using the Zinc strips at the peak of the roof.

I have also had good success with an annual "Moss be Gone" treatment on the trouble spots. I just tried to find the stuff I used to use, but it looks like it might not be available anymore.. It was a white granule powder that was applied dry, and rain would dissolve it and run it into the moss and kill it.

A ol' fashion push broom does a decent job as well.

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#8
In reply to #7

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 1:50 PM

I use Moss Out and buy it at Home Depot. There are two or three other products that seem to be similarly priced and just as effective. Here in the Pacific NW it's almost mandatory unless you have a metal roof (then it just grows around the fasteners).

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#9
In reply to #8

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 3:18 PM

RVZ/Pete,

I have used the powders, the liquids, the home remedies. They all do a great job but the lichen returns within a couple of weeks.

I will look up "Moss Out" though. I had not found this one during my research.

I have lived in this home since 2004 and had no problem until fall of 2009.

Roof was 4 years old when I moved in.

I have a row of assorted pines to the north and then swinging around to the west for wind block.

When the lichen originally started to grow I thought it was sap from the pines. The following spring I realized it was lichen.

I'm going to try the zinc (already bought it) and see what happens.

Thanks again for your input - KJK

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#10
In reply to #9

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 4:56 PM

Have you tried repeated dosings of a good Algaecide sold for swimming pools?

Milo

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#11
In reply to #10

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 5:05 PM

Hi Milo,

No have not tried that.

Are you thinking something like Shock?

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#13
In reply to #11

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 5:12 PM

no shock is a strong Chlorinator, he means a liquid algaecide to prevent algae growth. something like this.

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#14
In reply to #11

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 5:15 PM

Lichen is a symbiosis between a fungus and an algae. Pool chemical companies make specific algaecides I will send you a picture of the one I have at home tomorrow.,here's one off the web.

Shock and sanitizer are different. Algaecide is designed to kill algae.

Milo

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#12
In reply to #10

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 5:08 PM

Consan may work as well....

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#22
In reply to #12

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 8:15 AM

Milo/Rorschach,

Thanks for the product references, I will look into these.

Regards - KJK

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#15

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 8:31 PM

All the references I come up with from a Google search re: roof "damage" from lichen are from companies who sell stuff to kill it.

Do you have evidence that it causes damage, or do you just not like the appearance?

Personally, I thing it looks great. Also, lichen is very sensitive to pollution, so if you're growing a good crop, it implies your air quality is pretty good.

Learn to love it (unless you have good reason not to).

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#16
In reply to #15

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 8:46 PM

I think I agree with you - the lichen is very appealing. A green lichen of the great plains - and rather evenly spread across the shingles. Lichens are pioneers.. hell it's practically patriotic for an American of the great Western Plains to have them as pets...

I have this uglier orange stuff, growing only on the eaves at my house - not a bit pretty at a distance. Looks more like decay than a pioneer.. The green ones evidently prefer the rocks, around here...

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#25
In reply to #16

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 8:25 AM

artsmith,

I have seen pictures of moss covered roofs.

I agree to some extent that it looks appealing

My concern is that I don't want to replace the roof prematurely

Hopefully the zinc strips will take care of my problem.

I have noticed in my local that lichen grows on all kinds of surfaces that face north - north/west. Rocks, logs, wooden fence posts, hell I think I even saw it growing once on the side of one of my my neighbor's' cows

Regards - KJK

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#24
In reply to #15

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 8:18 AM

Hi John,

Yes, unfortunately lichen does cause damage.

As it grows it lifts the granules from the substrate leaving dark marks (substrate) behind.

From my research, lichen is not good for asphalt shingles, at least not good for cheaper shingles as I apparently have.

Regards - KJK

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#18

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 10:49 PM

Zinc in contact with aluminum is not a problem. In fact, aluminum is frequently coated with zinc prior to applying other finishes. They are close enough in the electromotive series that you won't have a corrosion problem.

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#26
In reply to #18

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 8:26 AM

welderman,

Thanks for the heads up. This was a concern for me, I did not want to eliminate one problem and create another.

Thanks again - KJK

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#19

Re: Will Zinc React Unfavorably with Aluminum

08/25/2011 11:13 PM

The zinc needs to be exposed to the rain and weather so that the formed zinc compounds wash down over the roof. It is the zinc compounds that kill the moss. With typical acid rain it forms, I believe, zinc sulphate salts. Perhaps someone can confirm the chemistry.

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#23
In reply to #19

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 8:17 AM

Concur on this note, the zinc must be exposed to the rain to wash zinc molecules down the roof to keep the algae spores from blooming.

A strip of lead would work as well. If you have any plumbing vent pipes with lead boots or galvanized covers around them you will probably notice that nothing grows below them on the roof.

It is the leaching of the heavy metals by the rain running down the roof that keeps it clean.

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#28
In reply to #23

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 8:32 AM

129CBRider,

Very good point!

I did notice no growth around the vent pipes.

My vents are zinc clad which is what got me looking into the zinc strips.

Thanks - KJK

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#27
In reply to #19

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 8:30 AM

Hi GW,

That is pretty much what I had assumed based on my research.

A neighbor of mine has zinc trips on the roof of his milk house that were installed about 15 years ago when he replaced the roof. The old boy swears by the stuff.

Thanks - KJK

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#21

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 6:05 AM

Here they apply a copper strip using double sided tape. Appears to work....

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#29
In reply to #21

Re: Will Zinc React Unfavorably with Aluminum

08/26/2011 8:43 AM

Hi Andy,

I had also read about copper but was concerned about the green patna (sp?) appearing and staining the shingles.

As Rorschach pointed out, there are also premium shingles available with copper oxide granules which I will look into when it is time to re-shingle.

Thanks for stopping in - Regards - KJK

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129CBRider (1); Andy Germany (1); artsmith (1); cuba_pete (2); GW (1); JohnDG (1); KJK/USA (11); lyn (1); Milo (2); Phaddy (1); PWSlack (1); Rorschach (4); RVZ717 (1); welderman (1)

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