Concrete Drying Time and Hydronic Heat

Discussion in 'HVAC Heating & Cooling' started by seaneys, Nov 2, 2007.

  1. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Hello,

    We poured our basement floor on Thursday morning. I'd really like to try out the hydronic heat (pex tubes in the concrete) tomorrow. Is there any reason to give the concrete a few more days to cure / dry?

    Thanks,
    Steve
  2. got_nailed

    got_nailed DIY Senior Member

    Messages:
    277
    You need to wait at least a week so it will cure a little before you start adding heat
  3. leejosepho

    leejosepho DIY scratch-pad engineer

    Concrete shrinks as it cools/cures, and to apply heat before it does so could fatigue it by way of expansion. If I were you, I would wait at least a week. Where I work, concrete tanks and dry wells are pulled from their forms after 24 hours and are then left alone for nearly three weeks before being delivered to job sites.
  4. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    Drying is not CURING. Curing is good; drying is bad.

    You want to be sure the concrete remains moist during the curing time.

    Concrete cures by the water forming chemical bonds with the the chemicals in the cement. If it dries before it is cured then the cure is incomplete and you get weak concrete and a dusty surface.

    The low humidity that occurs inside during the heating season will make it dry quickly so it is usually necessary to keep it moist with a mist or a wet cloth. You can also wet it and then cover it with plastic to keep it moist.

    Heating it from the inside with dry heat will probably damage the concrete.

    It should be cured for at least a week and the cure time for normal concrete to reach "specification strength" in 28 days.

    You get the strongest concrete when you use as little water as necessary when it is mixed (sloppy concrete is poor concrete), but then keep it moist after it initially sets. When I was working in road construction we would put the test specimens in a barrel of water about a day after they were poured. Factory concrete is often cured with low pressure steam because the wet heat accelerates the cure.
  5. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Hello,

    Thanks a lot for the great advice / information! I'll wait a week.

    Steve
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,896
    Location:
    New England
    Some of the stuff I've read says you should then start the heat, but take a week or more, bringing it slowly up to the desired level.
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