What is this White substance on Crawlspace lumber

[Randall Cole]

These pictures are from the wood flooring above the basement of a home built in 1930. What exactly is this white substance on the wood?

[Marcel R. Cyr]

Looks like white mold or the start of dry rot in the framing.
Some sort of fungi caused by the excessive moisture environment.

[Joe Funderburk, CMI]

The wood looks like it was treated with creosote, which was a common way to do pest control years ago. You may want to add a disclaimer about that chemical possibly being present.

I agree...the white stuff looks like mold.

[Randall Cole]

Thanks gentleman.

[Charles E. Quinlan]

Yeppers.

White rot.... most likely started, died out if not enough moisture was present. In spore form it will stick like glue to the surface, waiting for moisture.

Q