The Historic District

I recently bought a home built in 1870 with the remains of an old stone wall and fireplace in the dining room. I am seeing these places on the stone for the first time, I don’t recall seeing them before. Blue/green, some under white. Sort of powdery, smears when wiped with wet paper towel. Some places flake off, like paint but I know it’s not paint. Easy to remove - takes some scrubbing in some places but cones off rather easily. Mold??? Finding all sorts of “fun” things about owning an old home and this is the latest. Anyone know what this could be and how to really get rid of it? I don’t know if it’s growing, just noticed it. But I don’t recall seeing it before. Any suggestions greatly appreciated

Hello Treny, welcome to the District. I don’t think it’s mold. Could it be the remains of a blue clay paint that once covered the wall. It looks like your stone wall has been repointed some time in the resent past. Is this an out side wall? Interesting though is the lack of pointing in the second picture. I can’t really relate the second picture to the first.
We have some very smart people here, they might know more.

Tell us more about your home, and include pictures. We really like pictures.

Congratulations, not mold! I think everyone goes thru that phase, worrying about damp and wood and basements etc. Mold won't grow on stones - it likes wood, however.

It IS probably from dampness, tho that is usually not a problem. That appears to be a mineral leachate coming from the stone, called 'efflouresence'. I have some in my basement; the stones are sulfur-containing, the leachate is yellow, and is actually sulfur! You can smell it if you put some on your finger.

I wouldn't worry too much about it other than maybe taking a wire brush to it and then shop-vacc'ing the dust up. Do that every 10 yrs The other thing I've seen done is that ppl will parge the basement walls with mortar/lime, 2 coats, and give the 2nd coat a brush finish. But that is entirely non-restorational, although many people like it.

Are those dehumidifier knobs in the pic? Very good

Yes, more pics, please! ha ha

Gibson, I thought maybe fluorescence as well but had never seen it in blue, really I was not aware that it came in colours. All I have ever seen is the whiteish grey.

This might sound like a stupid question, but does it glow in the dark? If so, just call it a fairyland basement and cherish it.

Gothichome wrote:Gibson, I thought maybe fluorescence as well but had never seen it in blue, really I was not aware that it came in colours. All I have ever seen is the whiteish grey.

Yeah, Gothic - generally, it is white/grey. But I've seen a FEW cases of a bluish, or green 'hue' in it. I think it's just leached out of the stone and bringing with it copper salts, things like that. Over time. Or even before they set the stone!

Used to be a stone mason (among many other things), we'd see ALL kinds of stuff in basements!

Concur that it's efflorescence. Basically a powdery form of dissolved minerals. Slow groundwater seepage is usually the cause. As others have pointed out, the color can vary by the composition.

It's a common issue in below ground basements and cellars. I've seen it in houses built as recently as the early 2000s.

Yep. Sometimes you can find it coming from chimneys or brick fronts not long after their construction. Once you know to look for it, you'll see it all over...on brickwork mostly.

It is a big part of the 'why' for 'masonry sealer'. No worry in a stone basement. If concrete, one may seal it as it's unsightly, but on stones, it's part of the charm