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Concrete basement floor

trident | Posted in General Discussion on March 12, 2009 12:02pm

I had an addition built onto my home 3 yrs ago and the basement floor continues to “chaulk”.  I sweep it, vacume it, hose it down and it contiues to emit a chaulky substance which is so bad I have to take my shoes off before I go back upstairs.

The basement is unfinished and always will be and for that reason I did not pay to have to have the floor professionally finished.  It was poured and troweled level by the builder.  Anybody even know what is causing this?  It does suit my needs for simple storage but is there any remedy to this oversight?  Short of getting out a jackhammer?

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  1. DanH | Mar 12, 2009 12:12am | #1

    It's efflorescence, caused by moisture coming up through the floor and evaporating. As the water comes up it brings up "salts" with it, and those salts end up on the floor when the water evaporates. (Note that this "salt" is not table salt, but calcium compounds from the soil or dissolved out of the concrete.)

    You can temporarily lessen the problem (and remove the current powder) by washing the floor with a mild acid solution, but for a permanent fix you need to stop the water movement. This can be done by reducing the moisture level of the soil below the slab, or by coating the slab with a waterproof coating.

    The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
    1. ncproperties | Mar 12, 2009 02:18am | #2

      The builder didn't by chance water level the slab? That is soup up the mix to make it easy to place. They wouldn't tell you if they did anyway. A weak mix can leave the floor always chaulky as the surface basicly wears out. A strong floor sealer will help with the dust but you'll have to reapply every couple years since which ever the problem is it'll still remain under the sealer.

      1. calvin | Mar 12, 2009 02:33am | #3

        I'm agreeing.  Not all that powder is efflorescence generated.  A good test might be taping that pc. of visqueen down on the slab for a couple days.  See if there is moisture pushing up the salts.

        A good penetrating sealer might go a long way in holding it.  I've worked on some slabs that "remained dusty" well after finish.  Homowners would comment on the kids getting dirty-making the basement "unlivable".  All they really did was broom it-basically just pushing it around, never once getting it all up.  Acted almost like drywall dust on subfloor.  Once they vacuumed, mopped and sealed-no more reoccuring problem.

        Certainly wouldn't be costly or hard to try in a small area.A Great Place for Information, Comraderie, and a Sucker Punch.

        Remodeling Contractor just outside the Glass City.

        http://www.quittintime.com/

         

        1. trident | Mar 12, 2009 03:31pm | #7

          Calvin, I appreciate the time you took to give me a head start on my problem.  Thanks again...Good tip!

      2. trident | Mar 12, 2009 03:29pm | #6

        Thanks so much for the tip. 

    2. trident | Mar 12, 2009 03:29pm | #5

      Thanks Dan,  good info and I appreciate your help

  2. Brickie | Mar 12, 2009 02:34am | #4

    I think who ever finished the slab added water to the surface when he thought it was setting up too fast for him trowel smooth.  That would explain the chalkiness.

  3. peteshlagor | Mar 12, 2009 04:39pm | #8

    The boys are right.  You've caught water from somewhere.

    But it doesn't necessarily mean you're screwed.

    Check this out:

    http://www.miracote.com/index.php?href=productdetail&id=17

    It does mean that you gotta have a QUANTITATIVE water permeability test.  One that measures just how much water is coming thru.  Over 15 pounds and then you're screwed.

     

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