Odd concrete/block wall question...

[B@ssmaster]

I am gutting my basement, a 40 year old house. The foundation walls are poured walls approx 4' high, then standard cinder block another 4' or so stacked on top of it. The area has a high water table and is all clay.

The block/concrete walls were hidden by stud/sheetrock walls until a few weeks ago. There was 2-8" of airspace between the foundation and the stud walls.

At some point the foundation was painted a beige color before the stud walls were installed. On top of that is another coating, of varying coverage, that appears to be rust! I can't figure out why rust would be present on a block/concrete wall.

The “rust” has a reddish/brown coloration and seems to be formed in “crystals” or very small flakes, for lack of a better term. Very similar to corroding steel. It is very sporadic in "coverage", very thin in places, very prevalent in others. It does NOT appear to be any type of mold, at least as far as I can tell. Bleach has absolutely no effect on it. It does NOT wash off with a water/borax mix. CLR does produce a mild reaction and a very slight color change, but it is almost negligible. A putty knife cannot remove any trace of it. A wire brush will remove the bulk of it, but it leaves behind a dull brown finish, just as if I were wire brushing the top layer of rust of a car body panel or something similar. One last thing I noticed, near the top of the block wall, there is a margin where there is absolutely NO trace of this “material”, and the very edge of that material almost looks like it has brush strokes in it. I suppose it could be some form of waterproofing material, but the coverage is so sporadic I can’t see how that would have been its purpose…

Has anybody seen anything like this before?

Could it have been some old form of anti-mold coating? Maybe a waterproofing that has mostly flaked off? Or could it be some type of mold? It just doesn’t seem to have properties of anything organic, seems strictly mineral.

Any thoughts are appreciated.

[B@ssmaster]

Oh, and I forgot to mention, we have been in the house over 16 years and whatever this is pre-dates our ownership. So if it is a commercial product of some sort, it's been out for a while.

[CAMAN]

If bleach does nothing to it and CLR has a reaction then it sounds like efflorescence. It's moisture with iron in it coming through the concrete and depositing it on the surface of the concrete. Nothing to worry about IMO

[Down Deep]

It might be some form of mold.

[King Canada]

If bleach does nothing to it and CLR has a reaction then it sounds like efflorescence. It's moisture with iron in it coming through the concrete and depositing it on the surface of the concrete. Nothing to worry about IMO

Caman is right... don't worry about it.

[soldoncass]

I agree with : don't worry about it. That said, if I was going to cover the walls back up and finish the basement, I would use this opportunity to put a new coat of water proof paint on the concrete before covering it up. A 40 year old house almost always needs the OUTSIDE LEVEL raised though. Natural settling and washing away ,makes the landscaping" out of whack", after a few years. Get a good look at that, and make corrections for slope AWAY FROM the house. That is the best thing you can do to keep water pressures away from your house.

[Tom7227]

It wouldn't be fun but you could get it off with a wire brush on an angle grinder. If you're going to paint it I would expect that you'd get a better adhesion if it was down to the bare concrete.

[B@ssmaster]

Thanks everyone for your thoughts.

I wasn't too worried about it, and was leaning towards it being a mineral deposit of some sort, but I couldn't figure out the mechanism. Caman's response turned the light bulb on for me. I'm a technical person by nature, besides needing to know the “what” I usually need to know the “why/how” of things to be comfortable. That’s the part of the "puzzle" that was bugging me.

Taking care of it is easy, been doing all the standard stuff everyone mentioned. Proper landscaping/slope, gutters, etc over the last few years.

Tom7227 must be psychic. About two weeks before I posted the question, I started on it with an angle grinder and wire brush, and have been painting with a good concrete sealer. Figure I might as well clean it up a bit before I start the remodel......this is the same area after grinding/painting.

[pureinsanity]

Is that Conklin?

[Tom7227]

I'm not psychic, just a person who has encountered some really crummy stuff and have found that an angle grinder and a wire brush solves a lot of problems.

[CAMAN]

I find it funny you were asking this question AFTER doing work on it for two weeks. If it had turned out to be mold or something serious what would you have done?

Basement looks good though!

[B@ssmaster]

I was pretty sure it was a mineral issue of some sort, I just couldn't figure out how it was getting on the walls....

As a result, I wasn't too worried about any potential health issues doing the work.

Thanks for the info.