Irregular horizontal cracks

[Denray]

This is from a 70's do it yourself for a cabin in the woods. The horizontal cracks look very jagged. Displaced a bit at the exterior, but not so much in the crawl. Think it's just from a poor second pour??

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[Jerry Simon]

Any signs of corroding & expanding foundation re-bar?

[Denray]

Nope on the rebar ?

[Jim Katen]

That first picture looks like the concrete moved after it was placed, but before it set. Almost as if someone backed his truck into the forms after the pour.

[kurt]

The explanation is in the first sentence. It's a 70's DIY cabin. Some hippie was smoking some Humboldt bud and making a mess of things. My bet is somewhere around Katen's.....someone mashed the foundation, or the forms blew out, or......pass the bong.....I gotta think about this a second......

[John Kogel]

The span between the joists suggests something wasn't right with the builder. [:-magnify

Good bet there was no rebar laying around handy. Maybe it took 2 weekends to get the pour completed with a mixer and a shovel.

In earthquake country, I think they should shore up that foundation. They could pour footings for wide piers every 4 feet. Then posts can be set in there to take the weight off the crappy foundation.

[mjr6550]

To me it looks like the concrete expanded. If not corrosion of rebar it could be a reaction with the aggregate. The fact that it is a single line may relate to a cold joint. If its only happening at one location it is probably not a big concern.

[Jim Katen]

The span between the joists suggests something wasn't right with the builder. [:-magnify

Very common framing around here. 4x6 girders every four feet and car decking on top. It's a solid system.

[Jim Katen]

If you look carefully at the first picture, the crack begins and ends in the middle of the concrete, with no other cracks radiating from it. The concrete had to have been plastic when that crack formed. I've had forms blow out during pours and as the mass of concrete starts to slump, it can create cracks just like that.

[Denray]

Thank you everyone for the input!!

[tom2tone]

Is the "crack'' an actual crack or a cold joint where a second pour was placed on top? Where is the cabin located and how deep is the footing. In very cold climates where the footing is not below the frost line, all kinds of things can happen. Are there gutters on the cabin leading the rainwater away from the foundation? I would also check the bottom wall plates to look for displacement, as well as checking the floors and walls for movement. It is rare that you would find any rebar in that wall, it would likely only be in the footing. It's hard to determine the cause without a visual inspection.