brown powdery substance behind drywall on concrete foundation

We are gutting a basement bathroom that has had boards and drywall glued to the concrete foundation. We plan on redoing the walls with furring strips, insulation etc but on removing the old boards we are finding a brown powdery substance on the surface of the concrete, in some places in lines and clumps but not all over. It is kind of fibourous looking in nature when clumped together. Touched it with bleached with no reaction and also doesn't look like mold, also brushes off. But don't know what it could be. Maybe a silly question but could it be dirt leaching throught the concrete walls?
Done searches on mold and doesn't seem to apply to this stuff. The house is 38 years old and the old drywall could of been up for years.
Any ideas? Thanks Chris
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I am also interested in this. Anyone know the answer?
Thanks in advance.
Debbie

____ Deborah Oney Blood Recall / Withdrawal - Creutzfeldt-Jakob Disease (CJD) http://members.aol.com/debbieoney/blood.htm CJD Watch - The International CJD Tracker http://www.fortunecity.com/healthclub/cpr/349/part1cjd.htm
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Pour bleach on heavily and see if it changes color and size
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snipped-for-privacy@aol.com (DebbieOney) wrote in message

Could this be remanents of glue / adhesive? The arrangement seems it might be. I doubt it is "dirt leaching through the concrete walls". Is there some feature of the wall that consistently matches the location of the brown stuff? TB
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Thanks for the interest and suggestions. On talking to the people that were in the house before, they apparently had a red ant problem in the bathroom. Starting to think this is the remants of an ant nest because of the sponge appearance of it. Having taken some pics but don't think you can attach pictures on the newsgroup. Chris

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house is

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