Black foundation

Can anyone identify the problem on some of the cinder blocks at the base of the outside wall of my garage? I'm wondering what the black stuff is. It doesn't rub off, and it's unaffected by bleach. Photos appear on alt.test at time 5:49 pm, 3/17/08.
Thanks,
Ray
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On Mon, 17 Mar 2008 18:02:27 -0500, Ray K wrote:

I don't see the post there.
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Your post did not show. I don't know if alt.test allows binaries so you may want to try a different group.
The black is probably either mold or minerals seeping through if you have water around it.
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Ray K wrote:

Looks like grease or tar. Perhaps a previous owner did some engine work there.
--
Tony Sivori


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Can't see the photos, but is part of the foundation buried? Is the garage part of your house rather than a separate structure? Could it maybe be the tarring to waterproof the buried part?
Banty
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Banty wrote:

If you have the capability to search by message ID, here's the message ID of the OP's post to alt.test.
To me, looks like used motor oil or grease oozing out of porous concrete block. It appears to be on a flat surface that is horizontal at the base of a well shaded and perhaps covered by a carport exterior wall.
Of course, not being there to smell or touch or otherwise examine it closely puts one at a disadvantage.
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If it's as hard as a rock, so hard a steel-bristle brush has little effect, rub it with a vitamin C tablet. If that has an effect, it's black algae, and a swimming pool supply will have remover/s. http://www.intheswim.com/Pool-Chemicals/Sun-Pool-Chemicals/SUN-Black-Algae-Treatment -----
- gpsman
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gpsman wrote:

http://www.intheswim.com/Pool-Chemicals/Sun-Pool-Chemicals/SUN-Black-Algae-Treatment
tablet had was to whiten the black, like rubbing ordinary chalk on a sidewalk. I also dampened the vitamin C with water; no effect.
Thanks for the suggestion.
Ray
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Ray K wrote:

couldn't view the original posts will have better luck. Sometimes I just see the top photo; if I go to another message and then return to my message, both photos usually appear.
Subject: Black foundation. Time stamp 10:00 a.m. (Eastern Time), 3/18/08. Sender: Ray K
One of the long garage walls is common with the kitchen; the innermost wall across the width of the two-car garage is common with the laundry room. The floor of the house is 8 inches higher that the garage floor. There has never been water seepage into the garage for the eight years I've lived here, even though some of the mortar appears crumbly after 39 years.
The black is not tar or grease/oil, and as I originally stated, bleach does not affect it, so it's probably not mold. The corners where the black is darkest had been covered over with blobs of cement. When I chiseled away the excess cement - to make it look nicer - the black showed up, although there is also black at the opposite corner (where the foundation meets the cinder block that supports the outside wall).
It could just be minerals in the foundation, as someone suggested. Soon I will be painting it, but I don't want to just cover up what may be a problem.
Thanks,
Ray
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