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Community and Q&A

Concrete admixture for waterproofing?

R W | Posted in GBA Pro Help on

We are remodeling and converting some of the garage to living space. We are replacing the foundation stem walls and slab. We had some musty odors in the first floor of the home before starting the remodel, and want to be sure to mitigate any future issues (1 1/2 of the walls are below grade, the slab is at grade (hillside lot)

We will have sub slab drains, and foundation drains, as well as sub slab eps and a vapor barrier. As added protection I was thinking about a hydrophbic admixture for the concrete. Does anyone have experience with this ? Would you recommend? what to look out for? I was thinking of using for slab and foundation stem walls.


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  1. GBA Editor
    Martin Holladay | | #1

    I have never heard of the use of hydrophobic admixtures for residential concrete. As far as I know, these admixtures are used for commercial jobs (for example, for concrete roofs).

    I doubt that such an admixture is necessary. If you are interested in pursuing the question, I would find out whether your local Ready-Mix plant even offers the admixture as an option.

    It sounds like you have what you need to keep your slab dry. You want a layer of crushed stone that is at least 4 inches thick. That layer should include perforated pipes for drainage. Above the crushed stone you want a continuous horizontal layer of rigid foam. Above the foam you want a layer of polyethylene or some similar vapor barrier.

    If you have all those details, your slab should be dry.

  2. Jin Kazama | | #2

    Have you asked your local concrete plant if they keep this type of admixture in stock ?

    I have worked with this a little bit in the past,
    and most plants need to purchase a miminum quantity of the admixtures, which then
    are only good for a period of time ..and it usually is much more than any residential project could use..thus most are reluctant of using additives unless specified in a large project.

    I doubt it is necessary as Martin pointed out.

    If you still wish to help out here are things that would help :

    - increase slab thickness
    - discuss with plant about "latex" additives to concrete
    - specify high quality concrete mix ( "super plastifier" = less water = less porosity once cured )
    - smaller aggregates or a controlled batch ( better mix of aggregates = better packing )
    - acrylic or similar plastic top finish 24hours after placement

    Keep in mind that it will be nearly impossible to prevent structural cracks from forming in your slab.

    Some "crystalisation " admixtures exists, they might sell in smaller batch ..which with time
    ( and water ) grow crystals to fill voids left by water ... again might not be available easily.

    You should really investigate if this is necessary at all though.

  3. David Meiland | | #3

    Use more portland cement in your mix....

  4. Expert Member
    Malcolm Taylor | | #4

    I'll defer to the other posters on whether it is necessary, but if you do decide you want to go ahead i'd use Xypex. Many batch plants offer it as an add-mixture and it is extremely effective.

  5. Jin Kazama | | #5

    Nice product ...similar to most other crystal formers

    availability usually is the problem ..and the cost

    May be different in your parts! :)

  6. Expert Member

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