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Large Concrete Cracks in Basement
12

Large Concrete Cracks in Basement

Large Concrete Cracks in Basement

(OP)
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!









RE: Large Concrete Cracks in Basement

looks really ugly... more than shrinkage cracking... just a few questions: is the post and wall sitting on the slab? is the post and wall taking any load? what is the soil like under the slab? what is the construction of the slab?

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

-Dik

RE: Large Concrete Cracks in Basement

ADA and NFPA (egress) both have trip hazard limits at 1/4". I doubt either applies to this but it's a basis for comparison at least.

RE: Large Concrete Cracks in Basement

(OP)
Thanks guys.

I'm not sure if there's a footing under the (4) ply post. There SHOULD be, but who knows? The (4) ply is a post that continues through the floor and up to the roof. The (3) ply is header studs.

RE: Large Concrete Cracks in Basement

Yikes. Not surprised the builder would try to dodge this one. I've heard more horror stories than I care to admit about builders being really shady on warranty items.

Around me the go from a foundation to a framed enclosed house in two days. Can't imagine there is much if any oversight at all.

I'm with dik that's more than just shrinkage cracks. Any expansive soils in your neck of the woods?

RE: Large Concrete Cracks in Basement

What does the connection of the wall look like at the top and base? Typically those should be allowed to float. While likely not the chief cause of the problem it could be exasperating the issue.

RE: Large Concrete Cracks in Basement

Definitely has “yikes” factor to those cracks. I went to an ACI conference and got a crack card to measure severity of cracks. These are about the size of the whole card let alone the scale marks on the card. Can’t say I can really contribute to answers, but I have questions.

How would the post create cracks like this? It seems the top side of the slab would be in compression when considering flexure, would shear cracks present like that, or likely in a perimeter around the post?

Possibly there is expansive soil underneath?

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

RE: Large Concrete Cracks in Basement

Get yourself a hammer drill and determine the slab thickness, potential footing existence and soil quality.
That could certainly be shrinkage if a lot of water was added to the mix. The vertical offset might also be due to slab curling.

RE: Large Concrete Cracks in Basement

I remember when I was building my house, the contractor poured all the perimeter, interior continuous and interior spread footings.
The slab section consisted of 4" sand base with w.p. membrane.
When they came to put in the sand, they had this conveyor thing that shot the sand into the pad.
The sand covered up all of the interior footings although it was obvious where they were since slab dowels could be located.
We cleaned the sand and all was good. I'm with XR, get a hammer drill and see if you have solid concrete between the slab and footing (If one exists)

RE: Large Concrete Cracks in Basement

You need to find the building plans to determine what was specified.

BA

RE: Large Concrete Cracks in Basement

Wouldn't do any destructive investigations, without builder permission.

I would stick to non-destructive ways like ground penetrating radar or similar.

I would get plans like BA suggested.

And if possible find a reference that you can use similar to this from the Australian standards. Basically anything above damage level two is considered a defect in Aust.

RE: Large Concrete Cracks in Basement

In my jurisdiction there are not codified reference for crack widths in a residential concrete slab-on-grade. However, there are Construction Performance Guidelines published by Tarion that are a useful reference. Tarion is the agency that mediates between the contractors and new homeowners with respect to warranty work. Thus they publish a very comprehensive guide that determines what is considered a defect and what is considered acceptable construction tolerances, etc... It is by no means perfect, but it does contain some useful information. Download the guide and look up the concrete basement slab-on-grade section. In my area a typical residential slab-on-grade is 3" thick, unreinforced, and no control joints provided.

https://www.tarion.com/resources/construction-perf...

These can be difficult and costly to fully investigate. It looks like more than shrinkage cracks to me. Settlement? Settlement combined with part of the slab getting hung up on a strip footing? Heaving? (I looked at one place where we suspected the slab had cracked due to frost heave during winter construction), inadequate subgrade preparation (poor compaction, large stones under slab), poor soil, etc...

You could investigate this to death, or I have had success in the past A) listing as many potential causes of the deterioration (see above), B) proving the deterioration is beyond normal construction tolerances and then C) basically stating that all the potential causes were within the care and control of the contractor, therefore it is the contractors problem to fix.

RE: Large Concrete Cracks in Basement

Looks to me that a hammer-tap or chain drag survey would indicate voids under the slab. Cracks could indicate settlement has occurred due to the column load and poor soil support. Maybe little, if any slab reinforcing.
You might be able to detect a depression at upper floor levels bearing on this column.

RE: Large Concrete Cracks in Basement

My basement slab cracked through due to what we thought was simple external root invasion (lifting) at one corner.

Turns out the roots did invade, and were the focus of the cracks, but the original builder in 1977 has simply laid plastic over the hand-dug and hand-leveled basement slab. Places in the slab were as little as 1/2 inch thick, others were 4-5 inches thick where the concrete was used to "level" the irregular hole for the basement. Where the slab was thin, it cracked. There was no "connection" between the wall foundations (concrete block underground, or brick and frame wall where exposed) and the basement slab.

A simple drilled hole (1/2 inch or 3/4 inch dia) in several places will tell the average thickness, and confirm or deny the location of the needed pads under the vertical column load points. My opinion? No pad, or too small a pad under the 6x column load point, and the concrete slab is being either punched through, or has yielded already and is being driven down into the loose, but now-somewhat-compacted soil under the load point.

RE: Large Concrete Cracks in Basement

Likely shrinkage cracks. I'd leave them and expect a significant reduction in asking price. Enough reduction to replace the slab some day.

RE: Large Concrete Cracks in Basement

Quote (That could certainly be shrinkage if a lot of water was added to the mix)


I've never seen that much water...

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

-Dik

RE: Large Concrete Cracks in Basement

No, not 1/4 cracks, all located on the load-side of the vertical column load, radiating from that point load. Too much vertical movement for shrinkage cracking.

RE: Large Concrete Cracks in Basement

Blind Guess: it's cracking that started due to dry shrinkage (most of it happens during year 1), but the post load combined with poor (or no) soil support stressed the slab more than it could take. Reinforcement wasn't enough (or doesn't exist) to resist cracking so here it goes. If you have a Ferroscan in your possession it might be wort to scan locally, I suspect no rebar would come up.

RE: Large Concrete Cracks in Basement

CarlB if from voids under the slab are we thinking flexural cracks started on the tension side of the slab and progressed through the cross section all the way to the top? I’m not seeing a lot of talk about where the stresses are in the slab and why the cracks would open where they are.

Again I’m just stealing a piece of this post to try to learn!

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

RE: Large Concrete Cracks in Basement

(OP)
Thanks all. Trying to get building plans and will update soon.

RE: Large Concrete Cracks in Basement

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

RE: Large Concrete Cracks in Basement

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.

RE: Large Concrete Cracks in Basement

Quote (I suspect no rebar would come up.)


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

RE: Large Concrete Cracks in Basement

Quote (it's cracking that started due to dry shrinkage)


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

RE: Large Concrete Cracks in Basement

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.

RE: Large Concrete Cracks in Basement

2
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!

RE: Large Concrete Cracks in Basement

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.”

RE: Large Concrete Cracks in Basement

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.

RE: Large Concrete Cracks in Basement

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.

RE: Large Concrete Cracks in Basement

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

RE: Large Concrete Cracks in Basement

4
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.

RE: Large Concrete Cracks in Basement

(OP)
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.

RE: Large Concrete Cracks in Basement

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...). 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.

RE: Large Concrete Cracks in Basement

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.

RE: Large Concrete Cracks in Basement

Quote (Rebar in basement slab not placed properly.)


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

RE: Large Concrete Cracks in Basement

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.

RE: Large Concrete Cracks in Basement

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?

RE: Large Concrete Cracks in Basement

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

Quote (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

RE: Large Concrete Cracks in Basement

...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.

RE: Large Concrete Cracks in Basement

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.

RE: Large Concrete Cracks in Basement

I can tell you this. If this was my house, this would be a major problem. Maybe not major in the long term performance of the house but it's pretty unsightly and you'd need a pretty good argument to convince me this is reasonable performance after 1 year.

RE: Large Concrete Cracks in Basement

2
(OP)

Quote (Rabbit12)

I can tell you this. If this was my house, this would be a major problem. Maybe not major in the long term performance of the house but it's pretty unsightly and you'd need a pretty good argument to convince me this is reasonable performance after 1 year.

I'm with you but the problem is that the builder doesn't need to convince you that this is reasonable performance.

You need to convince the builder that it is not reasonable performance, and that they are legally obligated to fix it. Good ole' burden of proof.

RE: Large Concrete Cracks in Basement

I keep saying I am going to write a book on "Contractor, Engineer and Architect Excuses". My favorite one for a Contractor's excuse for new concrete that has big cracks is "We all know concrete cracks. I would be more afraid of concrete that did not crack than concrete that cracked like this."

Those cracks well exceed normal shrinkage.

RE: Large Concrete Cracks in Basement

Have the homeowner send the builder a letter which states that they've consulted an independent engineer who believes this damage represents a significant structural defect and that if they don't propose a remedy then they will be forced to pursue a legal remedy.

You don't need to convince the builder of shit. You need merely point out that this is (in your opinion) a breach of contract / warranty and if they refuse to acknowledge that then they'll have a lawsuit on their hands.

RE: Large Concrete Cracks in Basement

I understand that it's a cut throat market for Engineers in residential design and any squawking could lose you your next job but it's a darn shame that residential builders aren't held to higher standards and that this is "par for the course".

RE: Large Concrete Cracks in Basement

2
If you go up a floor or two are there any signs of this post settling, like cracks?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Large Concrete Cracks in Basement

Quote (My favorite one for a Contractor's excuse for new concrete that has big cracks is "We all know concrete cracks.)


50 years back, being a 'wise old engineer' then... I was sure that concrete will shrink... so much so that I told the contractor not to remove the plywood between concrete pours... the concrete would shrink and you could then pull the plywood out... if it's still standing, I bet the plywood is still there...

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

-Dik

RE: Large Concrete Cracks in Basement

Agree with Ron that this most likely started as shrinkage cracks (probably right after concrete was poured). As the shrinkage cracks grew, shear strength of slab was reduced at the crack locations due to loss of aggregate interlock. Eventually you ended up with a concentrated point load eccentrically located at the very corner of an isolated section of slab on grade. Naturally this condition resulted in settlement of the corner of the isolated section of slab locally at the corner under the concentrated point load.

Not sure what the 4-2x6 stud pack is there for, but the real load seems likely to be from the 3-2x4 stud pack (2 jack studs and a king stud) at the corner that is supporting the end of the header beam that can be seen in the photos above. The 2x4 wall is obviously load bearing as can be seen from the photos of the floor joists above. Around here (southeast US) that slab would most likely be nominal 4" thick with an 8"-12" deep by 12"-24" wide monolithically poured, thickened slab under that load bearing wall. Reinforcing in the slab would probably be 6x6 W1.4xW1.4 welded wire reinforcing that was not chaired properly and was stomped into the dirt at the bottom of the slab during placement of concrete. The thickened slab under the load bearing wall might or might not have 2-#4 longitudinal bottom bars specified.

Looking at the photos, I doubt if there is a thickened slab under the load bearing wall because I don't think the shrinkage cracks would propagate through the thickened area, but I would not bet on this. I would be curious to investigate the presence/location of a thickened slab by drilling through the slab.

Based on the photos, I would consider this a relatively significant structural deficiency, albeit related primarily to serviceability. If left unaddressed, that condition will definitely affect the marketability and value of the home if/when the owner attempts to sell it. I routinely assess much less significant "structural" concerns related to residential real estate transactions.

RE: Large Concrete Cracks in Basement

Quote (Ron)

favorite one for a Contractor's excuse for new concrete that has big cracks is "We all know concrete cracks. “

And no engineer has ever used that excuse, have they. lol

RE: Large Concrete Cracks in Basement

This is the standard lingo I hear from contractors...
"There are two kinds of concrete: 1) Concrete that is cracked. 2) Concrete that is gonna crack"

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