Help Identify Substance on Metal Door Frame

[Tim Kerce]

Commercial building inspection. Aluminum door frame and threshold. Bottom of door frames are rusting and threshold is showing signs of deterioration. This white substance was built up in several areas. Could it be leftover ice melt? It was the consistency of wet laundry detergent. Thanks.

[Jerry Peck]

Probably aluminum oxide or whatever corroding aluminum makes when the aluminum corrodes into that stuff.

Those are most likely aluminum, not steel, so it would be corrosion, not rust ... but ... I guess "rust" is a type of "corrosion" ...

[Scott Patterson]

Yes, ice melt salt will do exactly what you have in the photos.

[Jerry Peck]

Yes, ice melt salt will do exactly what you have in the photos.

Is that the left over salt used for melting the ice, or is that the aluminum corrosion the salt causes? Or is that possibly both?

[Lon Henderson]

If it came from the aluminum, you'll see deterioration of the aluminum. I lean toward salt. Salt doesn't get washed out from the edges of the frame as easily and since salt "attracts" moisture, there can be efflorescence along the edge of the frame over time. Aluminum oxide is usually like talc in my observations and not as coarse as detergent.

[Raymond Wand]

Could also be Urea or Calcium Chloride, both of which are deicing products.

Calcium Chloride is also used for dust control on dirt roads to keep the dust down and harden the surface.

And Urea is also a fertilizer.

FWIW.

[Steven Turetsky]

Iron oxidizes (rust).

Aluminum oxidizes too. In the form of a dull whitish patina that covers the material. The haze then protects it from further oxidation. Same thing with silver (tarnish), brass, etc.

When we polish these metals, the black that dirties the rag is the oxidation.

[Jerry Peck]

Iron oxidizes (rust).

Aluminum oxidizes too. In the form of a dull whitish patina that covers the material. The haze then protects it from further oxidation. Same thing with silver (tarnish), brass, etc.

When we polish these metals, the black that dirties the rag is the oxidation.

Iron also rusts through, and disappears over time as iron oxide.

Aluminum also corrodes through, and disappears over time as aluminum oxide.

I've many iron items "rusted out" and many aluminum items "corroded through". :)

[Tim Kerce]

Thank you gentlemen!