Settlement vs. shrinkage cracking
Settlement vs. shrinkage cracking
(OP)
I have a client with a cracked basement wall. I went to look at it and the attached picture is what I saw. It was about the same width, 1/8"-1/4" or so, all the way down to the second course from the bottom, where it tapered into nothing. As you can see, the guy she's buying the house from tried to put some crack filler on there to cover it up. There's also a concrete patio in front of this wall that has a crack in approximately the same location.
Now since it's a vertical crack, I think I can narrow down the causes to either settlement of the foundation, or shrinkage of the blocks. Is there any way I can be sure it's one versus the other?
Also, the lady told me her home inspector said this was an "active crack." How he determined that I don't understand. I couldn't see the crack moving, obviously, so unless he had some historical data, how could he know it's active?
Thanks.
Now since it's a vertical crack, I think I can narrow down the causes to either settlement of the foundation, or shrinkage of the blocks. Is there any way I can be sure it's one versus the other?
Also, the lady told me her home inspector said this was an "active crack." How he determined that I don't understand. I couldn't see the crack moving, obviously, so unless he had some historical data, how could he know it's active?
Thanks.






RE: Settlement vs. shrinkage cracking
RE: Settlement vs. shrinkage cracking
Without knowing more about the construction, it is a bit hard to tell; however, these are things I look for to help define the cracking....
Shrinkage cracks more often follow the mortar joints without cracking the block (there are exceptions, but this is more often seen)
Settlement cracks can show in the mortar joints are through the block. For your condition, it would appear that you have very slight end wall settlement, causing a reverse bending in the wall. This is also consistent with the crack in the patio; although I would expect a shrinkage crack or two in the patio given its aspect ratio.
To further compound the issue..... if the wall is restrained by the footing (doweled) but otherwise unreinforced, then you would see a shrinkage crack "die" near the bottom (at about the end of the dowels).
Sounds like your narrowing is correct, but to further differentiate (if it is necessary to do so...that's a pretty minor crack that could be easily monitored for movement), you will need to look closer at the construction, the soil types, tree growth near the house, changes in water table (including annual fluctuations), and an assessment of the construction. Consider that if the end walls are supporting the trusses, that you would be more likely to get settlement there, consistent with the observations. If that's not the case, then you're back to looking at all the other features and deciding.
Sorry to be of no more help than that, but more info would be needed to be definitive.
RE: Settlement vs. shrinkage cracking
RE: Settlement vs. shrinkage cracking
I don't think it's shrinkage because none of the other, longer walls have that problem, and like you said, the crack goes through the blocks and not just mortar joints.
RE: Settlement vs. shrinkage cracking
1) They all occured near the center of the basement wall (lengthwise),
2) There was no floor beams tying into that wall AND
3) The length of that basement wall approached 38 feet.
From my observations, those wall had earth pressure problems and no reinforcement in the walls. They were not soil settlement related.
RE: Settlement vs. shrinkage cracking
RE: Settlement vs. shrinkage cracking
Is there any?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Settlement vs. shrinkage cracking
Fixed earth, on this wall though, the floor joists do bear on it.
Regarding it being an active crack, it wasn't repaired and then re-repaired. The home inspector said that when he saw it, there was no crack filler on it and the edges were sharp, that's how he concluded that it was new and active.
RE: Settlement vs. shrinkage cracking
Yes, it's still possible the end walls have settled. The indication here is that the crack is wider at the top than at the bottom.
If the crack were caused by lateral earth pressure, it would show a consistent width or wider at the bottom, not the top.
RE: Settlement vs. shrinkage cracking
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Settlement vs. shrinkage cracking
If it's not settlement, I'm not sure what else it could be then.
RE: Settlement vs. shrinkage cracking
Could there be a large tree root putting pressure against the wall locally, perhaps uplifting the patio slab enought to crack it? I didn't see any obvious evidence of uplift in the photo though.
Do you know if the patio slab keyed or doweled into the wall?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Settlement vs. shrinkage cracking
RE: Settlement vs. shrinkage cracking
RE: Settlement vs. shrinkage cracking
hokie, the pipe exiting the garden is an extension of the downspout. The house is in Solon, Ohio, so I don't think there are expansive clays, but I could be wrong.
RE: Settlement vs. shrinkage cracking
BA
RE: Settlement vs. shrinkage cracking
Would you not agree that if the distress was caused by differential settlement, the cracks would follow the mortar and zig zag? The fact that the crack is near vertical and passes through solid block directs to me to say it is either lateral earth/water pressure. Also no cracks are rpeorted in the corners but I suspect this is near the center length of the wall, thus higher deflection (think of 5wl^4/384EI).
jay156;
What is the length of that problem wall? And could you tell us how close the crack location is to the center?
RE: Settlement vs. shrinkage cracking
RE: Settlement vs. shrinkage cracking
Wouldn't lateral earth/water pressure be more likely to cause horizontal cracks in the wall rather than vertical?
I don't think the problem is frost heave as the footer is about 3 to 4 feet beneath the frost depth. I suppose expansive clays might be present. The expansive clay map at geology.com says there are less than 50% of soils that may be slightly expansive in northeast ohio, so it's not out of the question, but I still think it's unlikely. I don't have the US geological survey map any more so I can't check.
RE: Settlement vs. shrinkage cracking
RE: Settlement vs. shrinkage cracking
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Settlement vs. shrinkage cracking
I was only involved in about 5 of these in the late 90's but it is more due to the lack of steel beam tying to that wall and the absence of any wall jogs to create a relief from the earth pressure.
Even in shoring design work, the soldier piles near the center of the wall length deflect more than the ones near the corner. Since there is no bowing and that the crack does not go through the footing, may be we can just replace some of the backfill in the center 1/3 of the wall length.
RE: Settlement vs. shrinkage cracking
The slab is probably a shrinkage situation as the concrete looks relatively new.
The wall damage is mostlikely lateral earth pressure damage for whatever reason - under-reinforced, plugged drain lines, clay, roots, etc.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Settlement vs. shrinkage cracking
I am not sure why lateral earth pressure would cause a vertical crack in a CMU wall? Bending over-stress in a basement wall, if you model it pinned-pinned, may result in horizontal cracks near the center of the inside face of the wall, no?
And as far as lateral pressure caused by tree roots, very unlikely. I had a forensic job where I had to extensively research this topic due to a retaining wall failure, and tree roots will grow along walls and foundations but they will not press against them. They seek the path of least resistance. They make commercial root barriers out of thin plastic. Not to be confused with damage caused by sidewalks or foundations built on TOP of tree roots.
Based on the info we have, and the vertical pattern of the crack, I agree with whoever said this is a differential foundation movement issue. Settlement at the center or heave at the ends, or vice versa, could cause a vertical crack. Though it'd be nice if it was more textbook and wider at the top or the bottom... If you think it may be clay is their anything drainage related you can put your finger on- downspouts, sprinkler heads, new driveway or altered drainage pattern.
Bottom line is a solution. Since the porch slab is right over top its not an easy demo and excavate situation. Geotechnical testing may or may not give you data that helps you solve the problem, sometimes, it gives you more questions (not that I am against it). Do you have a local geotech friend that knows the area and can tell the types of soils, especially expansive clay, that may be in that area?
Without any other distress I would proceed with a repair after thoroughly explaining the options to the client. This may be a band-aid fix or it may last 10 years or the lifetime of the house. It will be the least expensive option for now and at least you will then have a clean slate moving forward. If those cells are hollow at the crack I would likely sawcut out vertical slots to each side, dowel vertical rebar into the foundation and bond beam, and solid grout, with some horizontal "stitch" U bars. Hopefully there is a window to stick the concrete pumping hose thru! If the wall is solid grouted, epoxy injection in the crack.