Conditioned crawl space: cracks in newly poured cement floor


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Old 03-26-06, 05:49 PM
sbryanmb
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Question Conditioned crawl space: cracks in newly poured cement floor

I'm having a home buiilt that has a conditioned crawl space. The floor, of the crawlspace, is poured concrete. It was poured within the past week, during which time, we were experiencing temperatures below freezing. I remember that I was surprised that it had been poured beacause of the low temperatures. I was walking on it this afternoon and noticed several cracks in several different areas. None are wider than 1/16 of an inch, if they are even that wide. There is a vapor barrier, of plastic, beneath the poured concrete but I'm worried about whether or not this is normal, and if this is something that I should be concerned with. If it is something that I need to be concerned with, what is the best remedy?
 
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Old 03-26-06, 05:58 PM
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If it is conditioned, did the temp in the space fall below freezing? What is the size of the slab overall, and are there any control joints in the slab.
 
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Old 03-26-06, 08:40 PM
sbryanmb
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It is not yet a crawl space nor is it yet conditioned. The overall slab size is 1580sq ft. The temperature was at or below freezing on the day that the cement for the slab was poured. We also had freezing rain and snow that evening. The slab has been exposed to the elements from the time that it was poured (this being no more than eight days).

Control joints - are these the "seams" that are to allow for expansion and contraction? If so, no there aren't any - one solid slab.
 
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Old 03-27-06, 02:36 AM
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It is very common for slabs to crack within a week, especially larger slabs with no control joints. Cracks do not necessarily mean there's a problem. However, given the low temps, it may or may not have frozen. Some further questions:

1) Do the cracks originate at a corner, or where the concrete was poured around something (like a concrete block pier)?
2) Did the contractor use a freeze-guard type admixture in the concrete?
3) Just how low were the temps?
4) Was the slab covered or left open to the elements?
5) Is the surface of the concrete powdery?
6) Have you talked to the contractor or builder about your concerns, or asked about having it (the slab) tested?

Honestly, for a crawl space with a vapor barrier, I don't see much of a concern. It's not like you'll be doing anything on it like you would a basement or exterior concrete, so it won't get any wear and tear. If the concrete reached 500 psi before it froze it should be OK anyway.

Pecos
 
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Old 03-27-06, 04:54 AM
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Conditioned crawl space: cracks in newly poured cement floor

The air temperature was in the ranges you mentioned has little to do with the curing. The big factors are the soil or base temperature, the temperature of the concrete, the mix design and what kind of protection was used for the first 24 hours. Concrete generates heat during curing and the mass of the soil and the mass of the concrete help to maintain proper temperatures.

You will get shrinkage cracks in concrete, but they are more cosmetic than structural.
 
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Old 03-27-06, 04:18 PM
sbryanmb
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I really appreciate the responses that have been made.

In response to some of the questions that were asked:

-Some cracks do originate from corners, but most corners do not have cracks
-Don't know for sure if an additive was mixed with the concrete
-temps did not fall below 20 degrees the evening after it was poured
-the slab was uncover and left to the elements
-yes the surface of the slab is chalky
-I have not spoken to the builder yet, I didn't see the cracks until yesterday and I wanted an outside opinion first


The soil/base temperature was probably in the 30's when the slab was poured.
 
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Old 03-28-06, 02:47 AM
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If the soil temps were above freezing, I doubt that your concrete froze, at least until after it had reached sufficient strength. The very top layer of paste might have, hence the chalkiness. This isn't a problem for a crawl space as it would be for concrete that gets traffic on it.
The cracks originating at corners probably mean normal shrinkage, which is a good sign too. Concrete shrinks as it hydrates. It can't shrink around a corner so the concrete cracks there.
I think your slab is probably fine, but if you have concerns talk to your builder about them. Good luck with the new house.

Pecos
 
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Old 03-28-06, 04:27 AM
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Now that the author's concerns have been answered so well perhaps I can pose a question. I was just curious as to why you did not choose to add 5 or 6 courses of blocks and a deeper excavation and build a basement instead of a crawlspace? Was this building site quite wet perhaps?

Good luck with your newly constructed house.

bs5
 
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Old 03-28-06, 04:25 PM
sbryanmb
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Thumbs up

Once again, thanks to everyone for your replies.

In response to why a conditioned crawlspace - first and foremost, this was part of the builders package and wasn't optional, it was standardand the only option available to us.

Also, we live close to the coast and thus we are at sea level. We get a fair amount of rain during the year and in the area of our developement there have been problems of dampness and mold in neighboring developements. Most houses in this area have crawlspaces and basements are not the norm. A local builder/developer has been involved in a lawsuit regarding mold in recently built homes. I guess this was a safe alternative to the normal crawlspaces that are customary to the area.

I liked the fact of not having to crawl through a dark, dusty, damp crawlspace and not knowing what "critters" I may find as I'm crawling on my belly as I have to do at my other house.

Thank you all.
 
 

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