Residential post tensioning of slab not done - now cracked

[timsch]

Hello all,

My in-laws are having a home built that is under construction, with framing, plumbing & roof completed & windows & doors installed. It was noticed during a 3rd party inspection that it appeared that post-tensioning of the slab was never done. In digging into it, this was confirmed. A couple of days ago my wife was doing a walk-through and noticed a significant crack. She posted this issue here, which includes pictures. She went back today and swears that the crack has gotten wider

She's made calls today trying to line up an independent PE to provide an analysis, not trusting the one that the GC will line up. The GC is rushing to get this behind him and continue on and let her know this evening that he has lined up tensioners for tomorrow. Obviously time is of the essence for us, and I wish I had posted this here earlier, but things are moving very quickly, so better late than never.

Primary question: Can this oversight be properly corrected? What issues might arise in the future if the GC gets his way with tensioning it now and continuing on?

thanks.

 

[Tomfh]

Timsch,

No way is shrinkage finished by 6 weeks. Maybe 50% or thereabouts. After a few years it will be 90%+ complete.

 

[CELinOttawa]

I was taught "18 months to shrinkage of concrete", and similarly that significant modifications to existing heritage homes will likewise have an 18 month window for all the secondary stresses to work themselves out.

It is entirely correct that most cracks form within hours (I've been taught 6 hours for this one), but they open over time. That's because the initial shrinkage is rapid thanks to plasticity, and following the initial set slows considerably. It doesn't, technically, stop, but becomes imperceptible and negligible.

I've not been at this anywhere near as long as many around here, but after twenty years greatly focused on existing structures I have yet to see a perfect construction. This building has many other flaws. They all do.

I have a simply answer to your wife's question: Yes. I would move into this house with confidence. I would also watch for the secondary issues, and make sure I understand the limits of the builder's warranty.

I do not mean to sound callus, but you have a significant advantage knowing the issue. The next house will have issues as well, it becomes another roll of the dice as to whether you find out, how you find out, and what the consequences will be.

As an aside:

- Surprised to see a home owner walking around the site, and around here I would be careful about photos of feet on site without steel toes.

 

[timsch]

Thank you all very much for your input; it has been most helpful. I'm appreciative and humbled.

 

[Aesur]

Correct me if I'm wrong, but wouldn't you want to have the slab tensioned prior to building the structure? Once the structure is built, the structure may act against the tensioning of the tendons. Was a vapor barrier used? I would typically require a vapor barrier where a flooring system that relies on adhesives such as glue are used to hold down the flooring. I ask because it was mentioned a vinyl plank flooring is used and depending on how it is attached it could have future issues should water penetrate the cracks.

 

[TigerGuy]

Every PT project I've seen requires the tendons be stressed within 4 days of the pour. If the concrete hasn't reached stressing strength by then, the stressing is done to 50 percent. Isn't this a code issue?

Best of luck on this

 

[timsch]

TG, that was the point for my post. I felt and still do that they screwed up. A crack might have happened, but the separation and the dropping of one side wouldn't have if it had been tensioned properly. Unfortunately, with contract wording being what it is, we've got a weak hand. Shallow pockets don't help.

I agree with the others above that it'll likely be alright, meaning it'll last probably as long as any other built with our present level of quality....

 

[structengr23]

My brothers foundation in Dallas has a similar issue. They waited over a month to tension the cables. The house was fully dried in but no brick or sheetrock yet. The crack was probably over 1/4" to 3/8" wide. They stressed the tendons and the crack only minimally closed. They sent the builders engineer out and he had the crack filled with epoxy and then they put self leveling grout to bring the foundation surface to level as best they could. They put a membrane down prior to placing the flooring. You're supposed to tension the cable within 3-8 days of pouring slab after the concrete has reached around 2000 psi. The soils in the Dallas area have a high PVR, so this un-reinforced slab was loaded with framing and sat un-reinforced supporting load. Then they tensioned the cables. They haven't closed on the house. The builder did not follow proper procedures placing the slab. Basically, even after tensioning the cables, the deflection from the settling soils and load just locked in the deformed shape in my opinion. No way tensioning under load did the foundation regain its camber. It was already +50% loaded. I told them to request a PE sealed engineering assessment report with repair recommendation.

 

[timsch]

s23, I hope that your brother has better luck with the resolution that my in-laws did, who were basically told to pound sand, suck it up and accept the house as-is. The builder did have a PE to sign off on it, but his report was less than impressive in my opinion. The city inspector was concerned about the issue, and he did post a stop-work order on the front door, but that didn't stop the builder from going in that same day and tensioning the slab, which did pull the gap together more than I'd have anticipated. No ramifications from even going around the posted stop-work order. It's apparent who has the teeth in these agreements, and it's more than sad that it's not those who would enforce proper, industry approved procedures.