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John Dirks Jr

pock marks in block wall

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The house was built in 1955.

The block walls as seen from the basement and garage had pock marks in them. They were pretty much evenly distributed which makes me think it was some foreign material in the mix when the blocks were cast. A greyish powder was flaking out of the pock marks.

Ever seen anything like it? What could have caused this?

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It's rather hard to be sure, from those photos, John, but concrete block, from that time period were also nicknamed cinder block. Apparently, a lot of trash went into block back then, iron, slag, etc. (I've even seen strips of inner tube hanging out of cinder block.) At any rate, most likely what you're seeing is metal that rusted and expanded, much like steel lintels do over windows. The surface popped away.

As I said, these photos are a bit hard to read and be sure, but if there's any rust in there, that's most likely what's going on.

As a matter of fact, since you mention gray powder, it may actually be cinder (fly ash or bottom ash), which didn't get mixed in properly.

Even in the eighties, concrete block came in a couple of grades. One manufacturer made a product branded Solite, which was, as the name states, very light - easy to handle. On the other hand there was a concrete block that came out of Fredrick, MD that was an absolute ball busting 72 lbs for just one 12" block. (Now there's an isometric for you - ease 200 of those in a day down into a bed of mortar.) Obviously, the Fredrick block was the one to use if you were building a bomb shelter.

I've noticed that block back then often had very large aggregate and not enough fines, which made the block very porous.

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It's rather hard to be sure, from those photos, John, but concrete block, from that time period were also nicknamed cinder block. Apparently, a lot of trash went into block back then, iron, slag, etc. (I've even seen strips of inner tube hanging out of cinder block.) At any rate, most likely what you're seeing is metal that rusted and expanded, much like steel lintels do over windows. The surface popped away.

As I said, these photos are a bit hard to read and be sure, but if there's any rust in there, that's most likely what's going on.

As a matter of fact, since you mention gray powder, it may actually be cinder, that just didn't get mixed in properly.

I've noticed that block back then often had very large aggregate and not enough fines, which made the block very porous.

Thanks Mike. There was rust stains trailing downward from some of the pock marks. I figured it was material mixed in at manufacturing.

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It's from iron ore tailings used as aggregate in the mix. It's most common in CMUs manufactured from the late '40s through the mid '60s.

I had a woman selling a home tell the buyer that someone must have broken in decades ago and shot at all the basement walls with a shotgun.

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It's from iron ore tailings used as aggregate in the mix. It's most common in CMUs manufactured from the late '40s through the mid '60s.

I had a woman selling a home tell the buyer that someone must have broken in decades ago and shot at all the basement walls with a shotgun.

Thats funny because one of the things going through my head on site was, "did someone use this basement as a shooting gallery"

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A Shooting gallery would certainly be a more exciting and entertaining story than just that's how they made em back then.

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A Shooting gallery would certainly be a more exciting and entertaining story than just that's how they made em back then.

(Valentines Day massacre...)

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It's rather hard to be sure, from those photos, John, but concrete block, from that time period were also nicknamed cinder block. Apparently, a lot of trash went into block back then, iron, slag, etc. (I've even seen strips of inner tube hanging out of cinder block.) At any rate, most likely what you're seeing is metal that rusted and expanded, much like steel lintels do over windows. The surface popped away.

As I said, these photos are a bit hard to read and be sure, but if there's any rust in there, that's most likely what's going on.

As a matter of fact, since you mention gray powder, it may actually be cinder, that just didn't get mixed in properly.

I've noticed that block back then often had very large aggregate and not enough fines, which made the block very porous.

Thanks Mike. There was rust stains trailing downward from some of the pock marks. I figured it was material mixed in at manufacturing.

What Mike said is what we learned around here. One of the largest cinder block manufacturers in the state used ash and cinder from a local power plant that burned garbage. Some of the "undestroyed" organic matter in the cinders they used caused those pops over a period of time.

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