White Substance On Ducts and Metal???

[krigler (Kenny Rigler)]

@ldapkus

The mortar joints appear to be efflorescence. I have seen asbestos duct wrap and removed this product in the past. The material is removed by wetting the material and scraping it of with a flat scraper. When done halfassed, residue remains. A closer look would be needed to determine if this is that product. If not, it’s a moisture issue.

Linus, did you look at the forum link I posted above:

@bknowlton

That is oxidized zinc from the galvanized sheet metal. This happens if they leave the sheet metal stacked with moisture between sheets before it is formed into ducts. I have refused many shipments of sheet metal for this very reason. It is only a cosmetic problem as far as I can tell, but many customers balk when they see it.

In that scenario it seems it was simply a moisture problem during storage of the sheets and only cosmetic problem. But it seems you’re indicating it might be an asbestos residue issue. As I looked again at the previous post, they discussed not being able to scratch it off. Whereas when I tried it, it scratched off as a powdery substance. Which makes me think maybe it’s more like what you’re talking about. Did they still use asbestos wrapping in 1977? I know you only have pictures to work with, but do you have thoughts on which it might be?