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post tension v. traditional slab

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  • post tension v. traditional slab

    I am a construction manager for a large production home builder in Houston. My company builds 3000+ units a year through out the country. Here in Houston, our foundations are exclusively slab on grade post tension. We do not use turn key concrete companies. We truly "piece mill" our foundations, i.e. hire differnet subs for form set, plumbing grounds, make up, and pour. In addition we order our own concrete and make up material for our jobs.

    Here are your questions. Which do you prefer?

    Post tension vs. traditional, and why?
    Piece mill vs. turn key, and why?

  • #2
    Re: post tension v. traditional slab

    Post tension is usually required for expansive soil, is this your case?

    In most cases turn key is better as it eliminates many of the disputes between individual subs and makes for a better quality finish product. Also, if one delays another of if a pump breaks down it can become a scheduling nightmare.

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    • #3
      Re: post tension v. traditional slab

      Yes, we do have very expansive soil in Houston. We refer to it as "Gumbo." It contains alot of clay. However, I don't believe that's the reason that my or any other production company calls for post tension. I believe it's simply for costs, although no one would ever admit that. Most people who call for post tension will exclaim that is a superior system. Most "true" custom builders that I've talked to believe that post tension is inferior and will only call for a "conventional" or "traditional" foundation.

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      • #4
        Re: post tension v. traditional slab

        Yes, we do have very expansive soil in Houston. We refer to it as "Gumbo." It contains alot of clay. However, I don't believe that's the reason that my or any other production company calls for post tension. I believe it's simply for costs, although no one would ever admit that. Most people who call for post tension will exclaim that is a superior system. Most "true" custom builders that I've talked to believe that post tension is inferior and will only call for a "conventional" or "traditional" foundation.

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        • #5
          Re: post tension v. traditional slab

          According to the architect/builder that I used to work for (also in Houston), post-tension is **in theory** a very good system. However, in practice it ends up being flawed because it is an extremely difficult system to implement correctly. Everything has to be exactly right for the system to be effective: cables at just the right depth and spacing, just the right tension pulled on the cables at exactly the right time in the curing process, etc. He claims to have never seen one done correctly, even when he personally supervised every minute of the pour.

          Post-tension supposedly implements the "floating raft" concept: now matter how the soil moves, the slab will stay intact as one cohesive unit, "floating" as you will on the soil. Nice theory. I suppose it also saves a little on concrete and steel reinforcement, which I suspect is the real reason it so heavily favored by the production builders.

          That said, I would love to learn more about the building science behind the technique, especially since it seems like EVERY new production home in Houston these days uses it.

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          • #6
            Re: post tension v. traditional slab

            My past grey headed employers were very much against post tensioning. We had success with prestressing, but tranditional reinforced concrete is much more idiot proof. Lately, that it would make traditional construction essential.
            I also think it is impossible to get a good installation resulting in very high liability.

            Now that I am grey headed, post tensioned slabs is not in my vocabulary.

            glenn

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            • #7
              Re: post tension v. traditional slab

              Hi,

              You can get some pretty good information about post-tensioning on the site of one of JLC's sponsor's - The Concrete Network. Check it out at the link below.

              ONE TEAM - ONE FIGHT!!!

              Mike O'Handley
              hausdok@msn.com


              The Concrete Source

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