Corrosion to metal roof

[Bigboblargerobert]

Hi, new member here. A little background. I have a Kuma Tamarak wood stove that I mostly have burned dry, seasoned Douglas Fir. Occasionally I have burned ash, and oak. The outlet on the stove is 6" and expands to 8" at the ceiling . Stovepipe exhausts well above the roof line, and has a non screened chimney cap. Stove was installed 2013.

I have a standing rib PVDF metal roof installed in 2012. The cut ends of the metal roof panels (a total of four) below and adjacent to the stovepipe, have badly corroded. Additionally, there is a small area 4' below the stove pipe where the colored coating is flaking/peeling off. There is no discoloration or staining to the roof, just the effects of corrosion. I wont go in to the round and round with the metal roof supplier, they concluded I had a fire in my rain gutter. The short story is that they will provide new metal roofing if I pay the labor. My roofing contractor stated this is from run off from the creosote, however he hasn't seen this occur before.

I would like not to repeat this. All of that brings me to my question. What can I "wash" my metal roof with to neutralize the acid effects of the creosote, and at what frequency?

Thanks in advance for your thoughts. Bob

 

[begreen]

That is odd. Baking soda is a good, non-toxic acid neutralizer that should be safe.

 

[Grizzerbear]

Is there visible creosote on you roof? I have a metal roof and have never had a problem. The end of the metal panel does look like it got hot and boiled the paint off but hard to tell by looking at a picture

 

[Mech e]

That doesn't look like corrosion to me either; it looks like is got hot. Does the roof have the same appearance adjacent to the chimney as you mentioned?

 

[Bigboblargerobert]

There was no fire. I could post additional pictures of the inside of the rain gutter, and flashing that don't show any evidence of fire, but that's not why I'm here. My roofing contractor has already confirmed there was no fire, as I contended all along. He, the contractor, was able to get the metal supplier to admit privately the was no fire. They won't admit this to me, or discuss how to clean the roof of creosote to avoid a reoccurrence (since they deny this as the cause). They will supply the metal if I cover the labor.

It's been suggested to use backing soda to neutralize the creosote. Any other suggestions? Thanks again for your comments.

 

[Grizzerbear]

Is there a lot of visible creosote on your roof and chimney cap? If there is you might recheck the moisture content of that firewood because if it really is what is causing that metal to corrode.....and I'm not saying it isnt just never seen that before..... then your flue temps while burning are obviously to cool and that is creating the creosote.

 

[marty319]

I burn 24/7 and have had a metal roof for 10 years,no visible signs of creosote on my roof

 

[Mech e]

Bob, you mentioned that these are cut pieces, thus no corrosion protection across the thickness of the metal?? If so, I would contact the mfg or dealer and ask for recommendations to protect the exposed edges. I have used a lot of preplated sheet metal and the cut edges always rust.

 

[begreen]

I'm wondering if the issue here is the PVDF metal roof coating. It may not be up to spec?

 

[Bigboblargerobert]

Thanks for the responses. I'll answer the questions you have asked in order.

There is slight staining that I can remove with a damp rag, what I can reach (expand picture in first comment to see). I buy seasoned wood only, burning the oldest wood only. For example, this year I bought 2 cord of wood that I will burn the winter of 21, 22. This year I will burn wood that was purchased in 2019. I pretty much burn Douglas Fire exclusively so I doubt MC is a problem.

These are factory sheared pieces, that rely on a sharp shear to produce "crisp" edge and a galvinite undercoating to prevent/limit rusting. The supplier contends the damage is due to a fire in the rain gutter, and will not discuss preventing anything related to corrosion from creosote. I have prepared and coated the unaffected edges of the remaining parts of bottom edge with ZRC cold galvanizing.

The supplier will provide roofing, to be installed at my expense, so avoiding a repeat is greatly desirable.

Any other ideas to neutralize the corrosion? Baking soda has been suggested.

 

[Grizzerbear]

I have heard of a product called "rust guy" that when sprayed on rust neutralizes it. I have no experience with it but it's worth a look. After looking at your pic again it's obvious there was no fire. Your drip edge and gutter seem to be in good shape directly below the corroded panel.

 

[kennyp2339]

Spray some fluid film in the area, that has the corrosion, does not need to be the whole panel, just the ends near the gutter.

 

[begreen]

I have heard of a product called "rust guy" that when sprayed on rust neutralizes it. I have no experience with it but it's worth a look.

AKA Loctite Naval Jelly. Sold in bottles too.

 

[Highbeam]

Belly jelly is a rust converter. It’s acid and is not a preventative or a coating. Directions want you to rinse off unreacted jelly and then coat.

I like the zinc cold galvanization paint idea. I’ve cut lots of barn metal with shears or a saw and am amazed at how it doesn’t rust.

 

[begreen]

Yes, I have used naval jelly on a lot of stuff. Some I have just left but in critical locations I have followed with a protective coating.

 

[fire_man]

I'm wondering if the issue here is the PVDF metal roof coating. It may not be up to spec?

This makes the most sense to me.

If the OP has more pictures of other corroded areas (describing the specific roof locations) it would help unravel this mystery.

 

[Bigboblargerobert]

Thanks for the replies, and ideas for rust prevention. I have a four roof panels similarly effected as the one shown in the picture. The one I posted is the worst one. The supplier will furnish new roofing, so my interest is in neutralizing any corrosion due to creosote exposure in the future. Thanks.