New Home Under Construction Cracked Slab


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Old 11-10-07, 10:28 PM
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New Home Under Construction Cracked Slab

Hello, I was hoping you could help me with my problem. I have done extensive searching on the internet and on this site but it seems 90 percent of problems relate to basements and crawl space type homes. I have found some reference and threads relative to fine cracking in new home slab foundations but cannot seem to get the answers I am looking for.

This a new home and the slab was poured in August. I have noticed what is now about a 12 foot long diagonal meandering crack across the front right bedroom going from baseboard to baseboard. I can insert pennies and nickels in the crack at different places along the crack so it is no hairline crack. If you go outside and find the place even with the ending of the crack under the baseboard you will see a vertical crack in one of the cinderblocks or cement blocks that is obviously right in line with the crack in the slab.

I became concerned and hired a civil engineer/ professional engineer prior to signing the contract. Contract still has not been signed. The engineer told me that while the cracks are larger than he likes to see, he doesn't believe there is any structural damage although he commented that the crack in the outside cinderblock which is in line with the crack in the bedroom is the result of some footing movement or settling. But in his report he still says he believes there should be no structural problems.

Here is what I think I know. 4000 psi, fiber cement, danafill,no wire, poured on a day when the ambient temp was 105 which the following 3 days being 106 and then finally cooling to 102. I don't know if my terms are right here so bear with me. These figures were provided by the contractor and I did the research to determine those temperatures as the structural engineer had indicated the whole thing could be a result of pouring on a very hot day as indicated and the slab setting up too quickly and now having freezing temps. He only suggested the cracks be sealed, the yard kept 4 inches below slab level and the water routed way away from the slab.

My wife is killing me to get this thing. I am in my upper 40s and have purchased 7 or 8 homes in my lifetime, no problems. I just have a bad feeling here and am trying to get some guidance. I shouldnt have a bad feeling as I just forked over a lot of money to have an engineer tell me everthing was fine. Problems was I went to many other homes under construction, same type, singe level slab home, no basement or anything and could only fine hairline cracks and found no outside chain wall blocks vertically cracked.

I don't know, I hope you can offer some opinions. I have pics and the engineer's report if needed.

Thanks for your help.
FL
 
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Old 11-11-07, 04:45 AM
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Well, first off let me admit that I have poured plenty of concrete in my day. Any large concrete floor will check as it ages. When somebody asked for a guarantee it always included that fact. And I am sure that because this floor was poured on a 104* day only makes a prediction like this more certain. Concrete actually shrinks as it cures and in higher temp/low humidity areas this phonomenon is only accelerated. There are some measures the contractor can take to reduce the shrinkage like providing a visquine sheathing beneath and also after the floor is finished in order to slow down the hydration of the concrete, proper compaction of a granular base and providing some saw cuts so that when it does crack you have told the concrete where you would like that to occur..... pretty please. But perhaps his job schedule kept him quiite busy the next day and perhaps some of the precautions we excluded.

Now, my suggestion for your situation is to determine as best you can if this check/crack is more of a footing settling situation or just caused from early shrinkage of concrete. I assume this engineer you hired has shot the elevations of this structure with a transit to determine if we have any deviation here? If in the eyes of your engineer it is significant, then it should be addressed foremost. Do you know if there were any soil borings to determine ground bearing qualities taken prior to excavation for this job? Could they have pooured the footings on uncompacted fill?

bs5

It won't prevent cracking anyway but I was never sold on the effectiveness of fibres when compared with 6 X 6 steel mesh reinforcing.
 
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Old 11-11-07, 11:41 AM
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Originally Posted by bullshooter5
Well, first off let me admit that I have poured plenty of concrete in my day. Any large concrete floor will check as it ages. When somebody asked for a guarantee it always included that fact. And I am sure that because this floor was poured on a 104* day only makes a prediction like this more certain. Concrete actually shrinks as it cures and in higher temp/low humidity areas this phonomenon is only accelerated. There are some measures the contractor can take to reduce the shrinkage like providing a visquine sheathing beneath and also after the floor is finished in order to slow down the hydration of the concrete, proper compaction of a granular base and providing some saw cuts so that when it does crack you have told the concrete where you would like that to occur..... pretty please. But perhaps his job schedule kept him quiite busy the next day and perhaps some of the precautions we excluded.

Now, my suggestion for your situation is to determine as best you can if this check/crack is more of a footing settling situation or just caused from early shrinkage of concrete. I assume this engineer you hired has shot the elevations of this structure with a transit to determine if we have any deviation here? If in the eyes of your engineer it is significant, then it should be addressed foremost. Do you know if there were any soil borings to determine ground bearing qualities taken prior to excavation for this job? Could they have pooured the footings on uncompacted fill?

bs5

It won't prevent cracking anyway but I was never sold on the effectiveness of fibres when compared with 6 X 6 steel mesh reinforcing.
Thanks for your response. Yes I am confused too about whether he did decide they were shrinkage cracks or settlement cracks because in his report he refers to the heat when it was poured but in person he commented to me that there appeared to be some footing shifting or movement thus the crack in the exterior block. When I got the report it was 2 paragraphs, I guess I expected an extensive 4 or 5 page report which is why I did not take many notes on scene as he was measuring and making notes so I figured I would see all of this in his report, but wasn't there. I hesitate to email him back and politely ask for more as he is the college graduate and I am not. So I don't know.

No the engineeer did not pull out a transit so I know that wasn't done. He just looked around. Also I don't know about the soil borings. I would have to check with the contractor or the POA to confirm. I assume this had to have been done prior to pouring and cannot be done now.


Yes, about the fiber cement, I am a lay person where this is concerned but I was surprised to find out there was no wire in there as well and was not required because of the fiber cement.

Thanks again and I will try to get more answers.

If you think of anything else please let me know.
 
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Old 11-11-07, 12:24 PM
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New Home Under Construction Cracked Slab

It will take more measurements and probing to determine if it is a shrinkage crack or a foundation problem. Shrinkage cracks usually occur across a slab and not not across a corner. Granular soils (sandy) show early settlement (within a month ot two of placement usually).

Often, in hot weather, some contractors will use water in the mix to ease placement and extend the over-all finishing envelope. If you are in a hot dry climate, the aggregate can also suck more water out of the concrete as it cures, which can increase cracking.

The fact you have no wire for real crack control increases the likelyhood of shrinkage cracks. Unfortunately, any crack can isolate portions of a structure, causing the loads to be re-distributed over a smaller area on each side of the crack. This is when the combination of shrinkage, structural loads and soil problems accumulate.

I would look for a more thorough engineer. Any slab foundation crack the causes a crack in the walls suppporting your house is important. Since you apparently have a masonry home, the walls may be reinforced enough and stiff enough to carry the corner that may have lost some support.

Since this is a new home under construction, I would do everything to document the observed situation in detail to the contractor, who is required to provide a guarantee. Many times, documentation is more important than a short opinion at an early date in the life of the structure. At least, with a block home, you do not have to worry about the hurricane projectiles and uplift.

Dick
 
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Old 11-11-07, 01:01 PM
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Originally Posted by Concretemasonry
It will take more measurements and probing to determine if it is a shrinkage crack or a foundation problem. Shrinkage cracks usually occur across a slab and not not across a corner. Granular soils (sandy) show early settlement (within a month ot two of placement usually).

Often, in hot weather, some contractors will use water in the mix to ease placement and extend the over-all finishing envelope. If you are in a hot dry climate, the aggregate can also suck more water out of the concrete as it cures, which can increase cracking.

The fact you have no wire for real crack control increases the likelyhood of shrinkage cracks. Unfortunately, any crack can isolate portions of a structure, causing the loads to be re-distributed over a smaller area on each side of the crack. This is when the combination of shrinkage, structural loads and soil problems accumulate.

I would look for a more thorough engineer. Any slab foundation crack the causes a crack in the walls suppporting your house is important. Since you apparently have a masonry home, the walls may be reinforced enough and stiff enough to carry the corner that may have lost some support.

Since this is a new home under construction, I would do everything to document the observed situation in detail to the contractor, who is required to provide a guarantee. Many times, documentation is more important than a short opinion at an early date in the life of the structure. At least, with a block home, you do not have to worry about the hurricane projectiles and uplift.

Dick
Thanks for your response. When you say you assume I had a masonry home were you referring to the ouside walls or something underneath. The house will have a brick front and vinyl on the remaining 3 sides. However I think you were talking techinically about something below. I have had the hardest time understanding terms and how homes are built in different parts of the country. When I lived in Louisiana and they referred to a slab home. That is exactly what it was. The formed up the slab with wood, poured, popped the wood off and you had a big cement slab. Over in Arkansas where this home is at they build this cement block chain wall, put fill insided and pour the slab inside effectively leaving the form. And on that particular subject do you know, is this slab free floating within the block chain wall or is it attached somehow. You may tell me to just ask the contractor which I can do but he talks really technically and I nod a lot. Where I live at now in TN, they act insulted if you even act like you want a slab home. The people only want pier and beam construction, again if that is the right term, you know, a crawl space underneath with the block chain wall around the edges.

I think I understand now why most people don't want a slab home and would prefer pier and beam, if that is the right term. Thanks again
 
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Old 11-17-07, 10:13 AM
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One thing that the contractor just told me was that there was no water and no electricity to this lot until about 3 weeks after the slab was poured. So that tells me that they were unable to spray the slab to keep it wet in those high heat conditions. The only water they had was what was on the truck the day it was poured. That was it. That doesn't sound good.
 
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Old 11-17-07, 12:04 PM
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The finishing process and strength of concrete poured on hot dry days under low humidity conditions would be greatly benefited if it has a 4 mil thickness of visqueen carefully placed unpunctured and beneath the concrete. The water impermeable layer is placed directly on top of the compacted granular grade. After the floor is troweled and able to stand application of another layer of visqueen carefully weighted along the edges to reduce the loss of water by evaporation.

Based on your description of that crack, I tend to fear something other than rapid hydration of concrete is at the root of your trouble. It may be hard to tell at this point but can you sense any deviation of the plane of the floor on either side of the crack now? Has the crack widened significantly to anyones thinkng?

bs5
 

Last edited by bullshooter5; 11-17-07 at 12:06 PM. Reason: typos
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Old 11-17-07, 06:32 PM
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Originally Posted by bullshooter5
The finishing process and strength of concrete poured on hot dry days under low humidity conditions would be greatly benefited if it has a 4 mil thickness of visqueen carefully placed unpunctured and beneath the concrete. The water impermeable layer is placed directly on top of the compacted granular grade. After the floor is troweled and able to stand application of another layer of visqueen carefully weighted along the edges to reduce the loss of water by evaporation.

Based on your description of that crack, I tend to fear something other than rapid hydration of concrete is at the root of your trouble. It may be hard to tell at this point but can you sense any deviation of the plane of the floor on either side of the crack now? Has the crack widened significantly to anyones thinkng?

bs5
Thanks for your response. They used 6 mil visqueen under the concrete and do not know if they covered that day or not. I forgot to ask that and didn't think of it til right now when I read your post. I will find that out.

There is some deviation of the plane but less than a credit card thickness. Rake your shoe across it and you feel it. But it is lower on one section of the crack to the outside of the house but go a few more feet and you discover it is now slightly lower to the inside of the house so that deviation changes sides of the crack. The crack started as a hairline and now seems to have stabilized at about 1/8 inch thick, you know a little thicker than the width of a nickel.

And just to update, I have found other homes with similar cracks. So I don't know what to think. One thing is that the engineer I hired told me that he would consider the crack troublesome if there was more fill under that corner of the house. I didn't know what he meant until I had another fellow traslate that for me. And I am sure I am not telling you anything you don't know. But he was saying that because the right front corner of this home was only on 1 row of blocks it shouldn't be a problem. Now if the crack were at the back left where it stepped down to about 4 rows of blocks there may be some cause for concern because the slab is on much more fill back there. Does that make sense.
 
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Old 11-18-07, 06:29 AM
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Well, this is just my way of thinking. I hate to see any type of a weight bearing footing placed on any fill. A little clean and dampened sand compacted mechanically in layers is one thing but for my way of thinking footings should be placed on an undisturbed grade. Now, if that means an excavator has to dig a footing at different grades (instead of one level footing throughout) than so be it. The proper way would be to excavate deeper should the building site not be level and step the footing up or down as need be at 8" stepped increments if you are laying a block wall foundation.

You just can't trust any area that has been filled. What's beneath that footing? Brush, logs, marshmellows? Was the fill brought up from something substantial and in compacted layers in the first place? How do you know unless you take soil borings for compaction and load bearing capabilities just what they started with?

So to my way of thinking and if I understand your setting and layout accurately, I would say it can be a good thing if you are seeing portions of the foundation wall with more block layers than another area. If the building site is not level and they need to get away from providing some areas of fill to create a level site then they will step the footing or should. This way your on solid ground mother nature provided for you eons ago........not an area filled by the excavator on Monday and here comes a concrete contractor on Tuesdayand a redi mix truck pouring a footing on top before sundown. If that happens, it can lead to problems. Maybe you are going to be OK,don't take anything you read here as a deal breaker.

Yes, In answer to your question about making sense from the
engineers assessment of crack location......I agree with what he said.

.o2 cents worth while speculating from a long way away.

bs5
 
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Old 11-18-07, 07:34 PM
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imo, this is a random shrinkage crack

BUT, since its align'd w/a foundation crk, its very possible there's been some fnd. settling.

depending on the floor's finish, you might try patching the crk in 5 or 6 places w/plaster of paris - just bands 3" wide across the crack,,, ck in a day or so to see if the plaster's crk'd,,, if so, the conc's responding to thermal changes & this crack's now working as a joint.

are there sawcuts in this floor ?,,, these would've been made to control cracking ( control or contraction jnts ),,, possibly they could've been made the next day - too late when the temp's that high,,, when they came back to saw, the conc'd already crack'd,,, just too small for anyone to notice ( microcracking - .001"-.003" )

different houses, diff bldrs &/or diff subs ? ? ?,,, weather conditions ?,,, conc delivery ?,,, nothing's ever the same w/conc.

professionally i wouldn't argue w/your engineer but you need to invest a few years of dirty hands w/conc & conc repairs to really understand,,, congrats on doing your homework,,, now let's 'see' the pics,,, & let me know about the sawcuts, ok ?,,, its important.
 
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Old 11-18-07, 09:27 PM
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Originally Posted by so-elitecrete
BUT, since its align'd w/a foundation crk, its very possible there's been some fnd. settling.

depending on the floor's finish, you might try patching the crk in 5 or 6 places w/plaster of paris - just bands 3" wide across the crack,,, ck in a day or so to see if the plaster's crk'd,,, if so, the conc's responding to thermal changes & this crack's now working as a joint.

are there sawcuts in this floor ?,,, these would've been made to control cracking ( control or contraction jnts ),,, possibly they could've been made the next day - too late when the temp's that high,,, when they came back to saw, the conc'd already crack'd,,, just too small for anyone to notice ( microcracking - .001"-.003" )

different houses, diff bldrs &/or diff subs ? ? ?,,, weather conditions ?,,, conc delivery ?,,, nothing's ever the same w/conc.

professionally i wouldn't argue w/your engineer but you need to invest a few years of dirty hands w/conc & conc repairs to really understand,,, congrats on doing your homework,,, now let's 'see' the pics,,, & let me know about the sawcuts, ok ?,,, its important.
Hi thanks for your response, yes there were some sawcuts made. A rather large one at the opposite end of the house diagonally across the master bedroom from a corner to another corner. The engineer commented it looked like it had started cracking there and they made a cut on it. There is one on the other side of the house from corner to corner. One of those corners is where the major crack in the spare bedroom starts.

Yeah, about the engineer, I agree. I was told that there was no substitute for a guy who actually repaired and poured slabs for many years, who as you said, got his hands dirty. But as this point I have had so many opinions that vary so greatly I am very confused. Of course the only one to actually see the cracks up close and personal was the engineer. I wish I could get a foundation repair expert out there but I was lucky to find this engineer and the guys who actually do the work are just too busy.

Also I agree with you that the fact that the crack in the floor lined up with the vertical crack in the outside cement block would indicate settlement. And the engineer commented that way in the field but later told me that after thinking about it he felt it was not structural and that the vertical crack probably by sloppy concrete pouring at that point and that the crack was a continuation of the slab crack. I don't know.

I cannot see where the option is to post pics here. I will search and try to find that out and post a few.

Thanks again
Sammy
 
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Old 11-19-07, 05:28 AM
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that confirms my guess,,,

w/o actually 'seeing' it,,, the control jnts were cut TOO LATE,,, in that hi heat the day of the pour, you really have to be on your toes to get the cuts done at the proper time 'n' place,,, there're specific saws 'n' blades for that but its too late now.

what's the anticipated floor covering ?
 
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Old 11-19-07, 10:17 PM
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Originally Posted by so-elitecrete
w/o actually 'seeing' it,,, the control jnts were cut TOO LATE,,, in that hi heat the day of the pour, you really have to be on your toes to get the cuts done at the proper time 'n' place,,, there're specific saws 'n' blades for that but its too late now.

what's the anticipated floor covering ?

That sounds right about the cuts. In reference to the floor coverings I was always more concerned with structural integrity than the inability to put a particular floor covering over the cracked areas. But I do know where you are headed as the engineer asked the same question.

But as luck would have it all of the cracks are in each of the 3 bedrooms where carpet is going, with engineered hardwood going throughout the rest of the house so I guess I got lucky there as there is not a single crack, even hairline in nature in the rest of the house. Only 1 crack across each bedroom. Guess there is some good news.

Thanks
Sammy
 
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Old 11-19-07, 10:27 PM
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Incidentally, can anyone advise on the proper way to attach pics on this forum. I read the FAQs and I cannot find the Manage Attachments at the bottom of the post page. Can someone advise on that.

Sammy
 
 

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