Is the yellowish stuff on concrete mold?

[alex77]

See attached photo.

This is air duct space (crawl place? Not sure of vocab) above an office.

The top part is I believe concrete. See how there are parts that are yellow? What is that? mold? Efflorescence? Patched of insulation? If efflorescence or mold could it indicate an ongoing moisture problem that could be bad?

Thanks.

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[kurt]

Yes, can't tell from the photo, probably not, no, maybe, yes.

But it doesn't look it.

[alex77]

Thanks. Any other opinions?

[kurt]

What's the area smell like?

[Mike Lamb]

Is someone feeling sick?

[Marc]

There's this yellow colored OSB that was in use decades ago. Perhaps it was used to form this pour and the coloring stuck to the concrete.

Really can't tell without a closer photo.

Marc

[John Kogel]

If you could crop the picture down to just some of the yellow patches, I think we would be looking at fiberglass insulation.

The wall on the left is clean and dry and there is no visible sign of moisture on the ceiling tiles, right?

Bare concrete does not provide any food for mould to grow.

[David Meiland]

What's above that slab? Is there any reason they would have placed insulation against it?

There's always the possibility that some sort of form release agent was sprayed on the forms before the pour, and you're seeing some of it left over. Whatever it is, it was there before the channel was installed.

[alex77]

Thanks. This building was built in the 1980s.

[alex77]

Also, no, the ceiling tiles don't seem to have mold growth - from my pictures they appear white.

[alex77]

What's above that slab? Is there any reason they would have placed insulation against it?

There's always the possibility that some sort of form release agent was sprayed on the forms before the pour, and you're seeing some of it left over. Whatever it is, it was there before the channel was installed.

On the upper other side of the slab on the floor above is another office. I don't know if there is anything between the two offices or not.