Large Concrete Cracks in Basement 12

[cal91]

I was asked to look at some slab cracks in an unfinished basement. The house is coming up on a year old (when the warranty expires).

The builder was asked to come and look, and he said they were fine and they would not fix the cracks.

The cracks are near structural posts, and there is moderate elevation change across the crack. The side with the post is lower. I suspect there is not a thickened slab under the post and the post reaction has cracked through the slab. I have not seen any building plans however.

I am wondering if the IBC or some other source I could reference that defines acceptable crack widths and elevation differentials?

Any opinions would greatly be appreciated. Thanks!

 

[dik]

XR and BART have it... you need to get a set of drawings. You also need a 1/4 or 3/8 hammer drill and sink some holes through the slab. First a hole outside of the area to get the slab thickness. Get a small sledge hammer and drive a 1/4" or 3/8" rod down and see if you hit anything. There should be a top of the footing down there somewhere unless it's common in that area to build the footing directly under the slab. If so, then you'll find it when you drill through the slab.

If you don't find a footing and there's one on the drawings, you can inform the contractor. If no footing is shown, you can contact the engineer or the draftsperson that prepared the drawings if there is one. It can get a little messy...

You may have to retain a structural engineer, even if you are one, for an independent report to take this further.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[racookpe1978]

Actually, looking at the cracks again, they continue all along under the "room divider" floor beam (load point going towards the upper right of the floor photograph), not really concentrated only under the single 2x6 combined column floor board. Seems as if the it is the room divider wall section (the one made of 2x4's around the door frame) that is carrying the vertical load from the floor above, not just the 2x6 combined column going up to the roof. That bigger column looks like it is simply penetrating the through the upper floor above, not carrying the load of the floor above.

 

[dik]

In these environs, basement floor slabs often don't have rebar or WWM... also no sawcuts...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

way too big for that...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[epoxybot]

Well, as there is extensive cracking, (I think I see the crack trailing the the stud wall's bottom plate) and the cracking is radiating out, in four directions, from a heavily loaded point, with vertical displacement; there is good cause to demand the warranty be extended another year.

Can you request to review a copy of the plans at the Building Dept?

Would the home owner's insurance company render an opinion? I hate to say it but this could get legal.

Years ago in Diablo Valley, just west of the SF Bay Area, a housing track was going up west of Camino Tasajara and the builder, having completed a number of lots of foundation reinforcing (2 long cul-de-sac), including post-tensioning for the expansive clay soils, ordered up his concrete, just prior to the 4th of July weekend. The day of the poor was blistering hot and the method of cure was water laden carpet, wet cure. The site left only one employee to drive around and maintain the water saturation of the carpet. For those 3 days of the holiday weekend the heatwave continued, at over 100F. The water was not replace in a timely fashion and the slabs cracked. The houses were none the less, sold. Over the course of a year, the crack increased in size an quantity. Being single story, the only place they were noticeable was the garage floor; floor covering camouflaging the problems elsewhere. These slabs were tectonic plates! This large national home builder used every trick in the book to avoid responsibility. To heap pain on top of misery, the economy collapsed months later. I've searched but never found a class action by the home owners.

 

[XR250]

For this who do not think these can be shrinkage cracks have not spent enough time around tract builders trying to place 10 slabs on hot summer day!

 

[MegaStructures]

Could it be shrinkage cracks that have been opened by shear forces caused by the floor beam? Otherwise the floor beam force explanation isn’t making sense to me

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”

 

[dold]

I have a friend who worked for tract builder on the east coast. He was in the customer service "go out and investigate complaints" department. His description of his job was to go to peoples homes and try to stall them until the warranty ran out, then they would fight the claims with the argument that the buyer failed to do their due diligence in having the home inspected. He had to quit because he couldn't stand seeing people get screwed like that. He said slabs cracking was one of their biggest issues, almost always due to settlement (or improperly prepared sites, generally). One site near a big lake in North Carolina, the civil crew literally filled in a cove with 40 feet of fill and built about 20 houses on this....dirt pile. I'm sure they followed all compaction recommendations to a T. A couple of houses he said the slab had settled so bad that you could put your hand through the crack in the slab, and the roof had opened up. They had some shady (geotech) engineer on retainer who would always write letters about how the structure was not deficient and all issues are purely cosmetic.

/rant

But +1 to getting the drawings for the house. That 2x6 studpack looks like a last minute "lets get rid of this bearing wall in the living room" decision while they were framing. Especially how it is (isnt) framed at the floor.

 

[Enable]

Agree with XR250: Anyone suggesting that those cannot be shrinkage cracks has likely only observed shrinkage cracks as they appear in commercial applications (reinforced concrete and/or SOG with saw cuts & proper concrete specifications). Shrinkage cracks in reinforced concrete where the w/c ratio is typically 0.40, and slabs are wetcured(ish), are massively different from shrinkage cracks observed in unreinforced residential basements where the w/c is most likely 0.55 (before the contractor adds water because they were too cheap to order super-p), poured on a hot day, is placed well beyond expiry, and where the slab doesn’t even see drips of sweat let alone a proper wetcure.

Looks pretty garden variety. I concur that the post is probably not on a thickening and even if it is, this is residential where compaction usually involves bubba stomping on the gravel after raking it in. In short: probably poor all the way around. Meh.

What are you looking to do exactly? If you want to make a structural argument you could. If you want to make a durability argument you could. If you want to make a workmanship argument you could.

I’d probably figure out what you want first and then work backwards to find the justification for it. I suggest this only because you could claim any number of things here, and how far down the rabbit hole you want to go, will depend on your end goal or perhaps your client’s end goal.

 

[dik]

and the difference is elevation is shrinkage of the soil... go figgur...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

Yes, the cracks started as shrinkage cracks; however, the faulting at the crack is due to loading. The crack widened enough that the aggregate interlock could no longer handle the shear from the load on the post relative to the subgrade response.

Look at the plans and see if there was supposed to be some footing or thickened slab under the post. Next, do as others have noted...check the slab thickness and the compaction of the soil below the slab. Next do an auger boring down as far as you can do characterize the soils immediately below. If you don't see other distress in other areas, the soil influence is likely localized, either from lack of sufficient compaction or some near surface anomaly such as buried debris, a rotting tree stump, etc.

 

[cal91]

The contractor sent a photo of the floor plans for the basement, first floor, and second floor. Will be getting the full set of plans including notes and details from the city this week. The post has only 72 square feet of tributary area at the 2nd floor (master bedroom), and a 3x3 footing.

I've shown the homeowner this thread and gave them my opinion, to take pictures of measuring the crack width and vertical offset once a month until the warranty expires in June. If the crack doesn't noticeably expand by then, they can fill the crack and carpet over it when they finish the basement. If the crack continues to expand, they can take another stab at getting the builder to remedy the problem.

Thanks to all for your help! Very informative and I appreciate those don't hold back their differing opinions.

 

[Enable]

That sounds reasonable. Though, instead of having them measure the crack - which will be incredibly difficult to do reliably unless it opens quite a bit more - I would suggest placing a crack gauge over the most concerning area (see here:

https://www.grainger.ca/en/category/Crack-Monitors/Concrete-Testing/c/29045).

They are relatively inexpensive. But if that is too much hassle they can also go the oldschool route and place a piece of glass or hair across the opening and see what happens (glass will crack, hair will snap).

If nothing should result from the above, you may want to tell them to grind the high side down prior to covering. That kind of elevation difference will be noticeable, and annoying. Quick grind will take care of it though.

 

[JoshPlumSE]

I've seen many cases of homeowners complaining of small shrinkage cracks in concrete or in stucco or such.... This is NOT one of those cases. And, after only a year?! This is a significant problem and the builder is probably at fault. It could be a number of things:

1) Rebar in basement slab not placed properly.
2) Settlement due to insufficient soil compaction or geotech issues.
3) No thickened slab or footing where one was needed.
4) This could even be shrinkage cracks too. But, in a basement. I tend to think that it started as shrinkage cracks (as Ron said), but that a more serious structural issue is behind the reason why they've grown and displaced so much.

 

[dik]

There's lots of literature out there that notes that reinforcing steel in SOG construction is of little use.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[jayrod12]

I agree with the others that this is more serious than a "just monitor and see" issue. That amount of movement in one year, supporting a load bearing column is not acceptable. If I were the homeowner I'd actually just be breaking out a chunk of the slab there to confirm the presence of the 3 ft square footing. If it isn't there, then you know the cause of this, if it is, then hopefully the settlement/movement is finished. With that level of vertical movement between the two, I'd be concerned that whatever that post is supporting won't be level anymore.

And besides, you can't just carpet over a crack that large, if you remove a portion of the slab to do the investigation, you can just replace it with bag mix concrete and smooth out the transition.

 

[Enable]

Not just that dik. It can be detrimental because you cannot control cracking (saw cuts no longer aid as you are subject to random map cracking based on an unknown restraint condition).

But...this is a SOG in a residential basement (will have no RFT and no saw cuts). In the immortal words of Joseph Lstiburek "some of you need to get out more".

Problem? Yes. Builder's fault? Likely. Big issue? Very likely not.

Monitoring is the way to go. Even if the OP was to get the builder back what do you think they are going to do? They'll at best fill it with cement (not even epoxy). You would need to make a strong case for a structural integrity issue to get beyond that, and with no reports of cracked finishes above, that'd be a tough sell. They'll just say no. Then what?

 

[dik]

rebar helps minimise crack widths... my earlier comment:

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Enable]

...of course it reduces crack widths. The point I was making was that you cannot combine RFT and saw cuts and expect the saw cuts to weaken the slab enough to control location of cracks. This was marginally relevant based on your retort to Josh, but this is going in the direction of unhelpful so I'll leave that there.

For those seriously concerned, the first thing that you would check is for cracks in the finishes. A 1/4" deflection during service is ample to destroy all kinds of interior finishes. Next, since the basement is open you can also see if any members have pulled away from those that they support. After that, you would check deflection on the floor above to see if any dips are present in local area that are not typical of other areas in the floor assembly. If none of that occured (I suspect it would have been reported had that been the case) this is likely simple residential floor poured without a wet cure, on top of poorly compacted material, that moved during construction or shortly after. If you want to be certain you open up the floor. But big issue without cracks in finishes...no.

 

[JoshPlumSE]

There is a difference between a "Slab on Grade" and a "Structural Slab". A simple slab grade may only have WWF, which is fine. But, if this is supporting columns, then there must be a reinforced footing under the column (maybe in the form of a locally thickened slab). Or, the slab needs to be s "Structural Slab". This is a pretty significant screw up..... Now, if it had taken 10 years for this to happen, then I wouldn't be as concerned. But, after only a year? Definitely a major screw up by somebody, and the homeowner deserves a reasonable and permanent remedy.