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Concrete: Type, Thickness and Reinforcement

Constantin Member Posts: 3,796
1) For some reason I recall the floor being spec'ed out at 4,000psi concrete vs. 3,500 for the walls, but I'm probably wrong. Now where is my Gingko?

I'd consider asking the plant to add in a super-fluidizer to help level the floor from the outset if your concrete contractor thinks its a good idea. I wasn't here for the basement floor pour, so I have no idea of what happened.

2) Use a laser level, mark all the walls. Use that as a reference to get the top of the floor flat. The thickness below matters less as long as the insulation that limits heat loss is pretty uniform. I hear that a fine mix combined with a pump truck and a power trowel can be a sanity saver.

3) I would use mesh. It's stronger and it may protect the tubing from some abuse. Don't forget to throw some #4-60 rebar across re-entrant corners to prevent the slab from cracking there. Wrapping penetrations with sleeving helps also.

Lastly, if you live in an area where Radon is even a remote possibility, I'd put in the gravel and collection system now while it's still cheap.


  • Heatmeister_2
    Heatmeister_2 Member Posts: 88
    Concrete: Type, Thickness and Reinforcement

    Going to repour in two weeks. A few final questions.
    1) What kind if any concrete is recommended if any, 3500psi?

    2) Thickness: I am doing a repour and my basement is very tough to get perfectly level b/c of hard dry clay. I may have 3-4 inches in spots over the 2" styro. Is this ok?

    3) Should we use the fiberglass addative a $10/yard (total of 13yds) or use mesh over the pex?

  • Brad White_9
    Brad White_9 Member Posts: 2,440
    I would add to that sage advice

    a vapor barrier, two layers of 6 mil poly with rolled seams or other impermeable membrane.

    4000 psi is plenty for even a garage floor. You can get higher but it is harder to work. 3000 psi is a default minimum. That is what I used on basement floors over screeded dirt with vapor barrier and crushed stone.
  • Heatmeister_2
    Heatmeister_2 Member Posts: 88
    Thanks, but....

    On your #3 I apologize, but, what are "re-entrant" corners and I assume what you refer to as "penetrations" would be waste vents or anything like that

    On your Radon comments, I haven't a clue......can you ellaborate on what is entailed in a collection system?

  • hr
    hr Member Posts: 6,106
    An expansion

    strip and thermal break where the new pour touched the foundation walls is a good touch. It helps with cracking from external restraint, whereas the slab is poured within 4 concrete walls.

    Concrete supply places have strip precut for this, or use 1/2 foam.

    How will you fasten the tube to the foam? If you have foam clips or staples, I'd skip the wire mesh altogether. It doesn't do much reinforcing at the bottom of the pour. It's only purpose is to hold the tube spacing, in that placement.

    I think fibermesh helps, but even it doesn't prevent cracking or the traveling of cracks :)

    It's kind of a pain to get a nice finish on.

    What will the final floor covering be, again?

    Get the subgrade a smooth as possible. If it is hilly or rough the foamboards will crack as you walk on them. personally I think 2" foam is a bit overkill in a basement slab, but it is r-value.

    The more consistent the slab thickness the less it will crack. So the pros tell me :) You don't want 6 inches in some places and 3 in others. A little extra time spent on the subgrade is generally worth it.

    hot rod

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