White chalky mold (?) on wood beams

Hi all,
I recently bought a 130 year old house. The original floor beams are in the basement with new portions built in three directions. Therefore, I have both old wood and new wood in the same general area. I have had a little water in the basement, but I've fixed that and run a dehumidifier - so it's pretty dry now. I suspect it was not so dry in the years before I owned it, however.
Anyway, after about 1 year I noticed some white chalky powder stuff (I assume mold) on the basement beams - but only on the old wood. It was not there when I bought the house. I have cleaned most of it off with Bleach, but am having trouble getting it all off since the wood it pretty rough. Before I invest a bunch of time to get it ALL off, I wanted to be sure it was mold, or something else that needed to come off.
The stuff is pure white - it actually looks like someone splashed white paint on the beams. There is no black or green visible. It wipes off with a finger like chalk and covers a pretty big area across the basement ceiling (but very spotty). I suspect effervescence, except it's on wood beams with the living area (upstairs) on the other side of it.
Does anyone know what this is? I've never heard of mold like this before!
Thanks in advance, -Scott
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I have seen a lot of on wood in damp crawlspaces. Turn the dehumidifier to a dryer setting or get a bigger or additional dehumidifier. Also check into the possibility that damp air is leaking in from outside causing the problem. Also check into the possibility that water spilled onto the floor above or you may have a plumbing leak between the basement ceiling and the floor above.
Stretch
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Read this article:
http://alsnetbiz.com/homeimprovement/woodrot.html
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