How concerned should I be about foundation cracks?

[FrugalBeard]

Moved into 100-year-old house last fall. Previous owner did major fixer-upper stuff, and we're ok with little things not being perfect, it's an old house. That said I don't have the knowledge for how concerned I should be about foundation cracks... There are several of various qualities, mostly what I think would be called hairline vertical cracks, some with a white outline like they were patched with something and some of those which look like they may need redoing. I can get into details and/or pics if necessary, but are there rules of thumb for how generally concerned I should be if nothing's leaking and I don't think they're getting worse? I've been watching some YouTube videos on foundation repair but I'm not sure if I would know what I was doing. I'd rather aggressively pay off the house in 5-6 years first than drip money on multi-hundred-dollar patches but I don't want to risk multi-thousand-dollar structural damage.

(If it helps I'm in the Midwest, so full range of temps and precipitation... Also I assume the foundation is concrete, but it looks like large "bricks" rather than a single slab. I think the house might be stucco - it's bumpy and definitely not brick or wood or vinyl... I'm willing to learn but fairly ignorant : )

[Pooplips]

Do all the doors close easily? Easy way to tell if it's still relatively level.

If the cracks are perfectly vertical and very thin it could be that the wall just relieved itself because there wasn't a construction joint. Not a big deal.

If the cracks zig zag along the block pattern you may have some settling/earth retention issues.

Either way you should begin to monitor the biggest cracks. Take a black marker and make a straight line perpendicular to the cracks. If possible get a small ruler and try to measure the width to get a baseline. Come back every couple months and make sure you black line is still straight and the width isn't getting worse.

Any leaking cracks, you may want to get those sealed. Water sucks.

[MikeBear]

Sagging floor or roof line anywhere? Any ground water coming through?

Some thin cracks in block foundation can be fairly normal, and do not always cause issues requiring immediate repair. However, if you detect any sags and such anywhere, I suggest checking with a structural engineer ASAP. If the footings are inadequate, that can cause this, and has potential to be quite expensive to repair.

If there's any water coming through, but the cracks are stable and not causing sags, you can patch them with Hydraulic cement. That's basically an epoxy, and works very well if you do the prep work properly.

[paddedhat]

Pretty hard to imagine a foundation without a few hairline cracks, I've built dozens, and every one has at least one. If is a hairline, it's less than an eight of an inch, or so, in width. If it's clean and dry, don't worry about it too much. Hydraulic cement is cheap and easy to work with, but it is not epoxy, by any stretch. Pick up a small can of it, and a " margin trowel" and try packing the crack with the cement. If your foundation is large brick like units, typically 8" tall and 16" side, it is a "block" foundation. These are typically adequate, but not nearly as strong as a poured wall. Cracks in block are also extremely common, typically follow the mortar joints between blocks, and are typically harmless. Remember it doesn't matter if it's a stuccoed wall above grade, a block wall, or a poured concrete wall, small cracks are common and typically harmless. Big cracks, moving cracks, cracks with water or mud flowing through, severe settling issues inside the house, doors jamming, an other significant issues need to be looked at.

[Spork]

I don't live in an area with vertical foundations.  Our freeze line is shallow... no basements.  And our foundations are normally concrete slab.

Hairline cracks are not just common... they're expected.   Our floor is polished concrete and we were told when we built "cracks will happen and they're part of the 'ambiance' of that kind of floor.  If you don't like that: say something now!"

I've lived in a house with major foundation issues.  It sucks.  My symptoms:  (Caveat: again: this is horizontal slab, not vertical like yours.)
* cracks are not hairline.  1/8-1/4 inch in spots. 
* There is some shear to the cracks.  In other words, floor isn't level across the crack.  One side is higher.
* Doors not closing.  Even worse: doors seriously dragging and doing so seasonally.  In other words: in the summer, I'd have to rehang the door (every summer!) because it seriously drug on the bottom.  In the winter I would have to rehang it again because it drug on the top.
* Feel movement when a car goes into the garage
* constant patching of drywall cracks at the tape joints -- sometimes with some buckling or shear.
* plumbing issues... Drain lines develop low spots due to movement.  Occasional freshwater breaks where pipes pull apart.
* unlevel floors.  (Though, this was severe enough that I'm pretty sure it was just a shitty job levelling the slab, not movement.)
* cracking floor tiles.  (Again: most likely a shitty job.  No isolation membrane in there.)
* Chimney movement.  These are large, vertical, heavy things.  This makes them likely to move a little and it's easy to see.  In other words, it might be tight against a wall at the floor and pulling away from the trim at the ceiling.
* Roof leaks around moving items.... i.e: again, things like chimneys or house add-ons or roof line changes where flashing can start to pull away with movement.

Edit to add:

Do you live in an area with expansive soil?  Clay soils are terrible about this.  In wet seasons, they expand.  In dry seasons, they contract.  It can be hell on foundations.  In areas with very expansive soil, you will need to water the perimeter of the house to try to keep the soil as constant as possible.

[FrugalBeard]

Thanks, all. No sagging/door issues at the moment. I was talking about it with a contractor friend and he talked about epoxy injection and ports.. Looking into that, I wonder if maybe I'm not describing the issue very well, cuz the biggest crack is nowhere near long enough for spacing ports, and it's on the outside, not the inside. Since pictures = 1000x words I figured I'd try a few here.

I measured the widest crack and it is right on the money at 1/8". (first pic) It runs about 10 inches in length from the bottom of the "window" (actually an old coal chute, or so I'm told) to the ground. I'm assuming the white bordering is from some previous patch job.

Doesn't look like anything's happening from the inside (second pic). Does that mean I don't need to be concerned, or is the outside width enough to warrant patching?

[Spork]

I am in no way qualified to render an opinion here... but I wouldn't worry about them. 

[Bob W]

There are two types of concrete foundations. >. Those that are cracked and those that will crack.     Personally,  I wouldn't stress in it.

[paddedhat]

Actually, there was a crack on the interior, it's filled with caulk and painted. Bottom is there is nothing to worry about here. Caulk the exterior and forget about it.