Staining On Chimney Chase Top

LNG24

Here is the problem. Customer has a newer house built in '95. The oil burner is serviced yearly. The customer is getting rust color staining on the aluminium chimney chase top as well as chimney chase. I was told by one person that this is caused by the minerals in oil and the cap being too close to the top. As you can see in the picture, the cap is at least 12" above the top.

Any ideas why the rust?

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Ed the Roofer

I noticed from the photo, that the 2 points of origin for the rusty discoloration are the storm collar of the pipe to the right and the penetrations from the anchoring screws.

Could the dissimilar metal properties be antagonizing this situation. I do not know what will clean off the rust stains, but I have remedied this situation in the past by sanding down the sheet metal, making sure that the metal was clean, then using a polyurethane caulk such as Vulkem to seal the screw heads and then to paint the exterior sheet metal cap and pipes with a Rustoleum tyoe of paint.

For additional weathering protection, there is a clear liquid gel that is brushable. It is made by Geocel, and creates a brushed on clear silicone protective coating. Try to use a paint color which will be color coordinated with eithr their siding or roofing color scheme for a desirable looking final appearance.

Ed

LNG24

Thanks Ed,

I will be replacing the top completely. I only need to clean the vinyl. Dissimilar metals is a good theroy. I hadn't thought of that. I could swear that the top was aluminium when I was up there though it does look freckeled in the picture which would be galvanized and in either case if galvanized and aluminium contact each other there will be rust. So maybe the collar and the top are different metals. I had one person tell me that the rust staining is coming from the minerals in the oil!

Still looking for more opnions.

Ed the Roofer

I would still suggest painting of the pipes for cosmetic and down the road cosmetic maintenance issues. Make sure that if it is a hat pipe, that you use one of the heat resistant paint products.

The cap itself looks like galvanized to me. Chinese produced screws now-a-days have inferior coatings, (so I am told-how would I really know), and the reaction between dissimilar metals created a chemical reaction dependant on how far apart they are on the galvanic chart. I forget what it is, bu check out a S.M.A.C.N.A manual. I order alot of specialty items through Copperfield Chimney Supply, and just by browsing through the product catalogue, I pick up information well worth while.

Final point, whether you install a new cap or re-utilize the existing one, I did not notice a cross-break to pitch the water to the edges. If you notice the stains next to the screws, that is probably because they are counter-sunk too tightly creating a dimple or recessed area for water to accumulate and progress with whatever type of corrosion is occuring.

In my opinion, I do not buy into the theory about the oils creating this staining, but that is beyond my woring knowledge, so just an opinion.

Ed

PIPES

The rust is caused by chemistry of the flue gases. Replace the cap with stainless steel , a bit costly but worth every penny.

LNG24

So switching to stainless is the answer and will eliminate the staining?

If you want to hear costly...the homeowner had hired another contractor to do the job. They were quoted $1,500 which was paind up front! Yes up front. You know what comes next, he never showed up to do the work. I gave them advice on going after the guy and as of this past week, he was arrested! Turns out, he does this to a lot of people.