Limestone Rust Stain

I’m curious if anyone knows what exactly causes these pitted rust stains to form on limestone. The client has them sporadically over their exterior home. Best guess, this is some form of iron staining seeping through stone pores.

They have iron in those pieces of limestone I’m assuming. And when it’s in contact with water it’ll rust. Might be they used metal mesh

1 Like

Correct it’s iron deposits in the stone. It’s needs to be cleaned and the iron needs to be chiseled and drilled out. Major pass no thanks lol


Iron sulfide mineral (pyrrhotite), is what I found on a concrete foundation inspection site. It’s random staining all over the home, no pattern what so ever.

The guy is 817 area code which happens to be my neighbor making him good people lol


The mineral that’s oxidizing in the stones due to moisture/ oxygen, could cease with simple stone sealers after cleaning. The chisel and drill method may be a solution, but I can’t find any material on this.

Cleaning the stone will be straight forward, quick and affordable, but not guaranteed the staining may return after sealing… Since this is the first time I’ve seen sporadic rust seeping from stone with no metal anchors and it’s not in the foundation, or motar around the stones…it may work

It’s non invasive, no drilling, no chiseling…

To truly get rid of those stains for good ,you’ll have to get the iron out.

The limestone most likely was cut from the same quarry…then delivered as is.

The client is scheduled in two weeks for exterior cleaning, following selected stone sealing. Time will tell if a moisture barrier will work.