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Need to seal a new cement basement floor

MPdjjBwcfD | Posted in General Questions on

I just poured cement over compacted sand( Michigan Dirt Floor w/field stone foundation).
Has been down and drying for two months.

Relatively nicely dry until a prolonged rain which leaves the sand damp only.
I have the typical dusting surface on my new cement. ( NAME?).

I want to seal the surface to keep the dusting down and make the surface cleanable. As the vapor barrier is under the cement – I assume it will/should breath through the sealer. Whats the theory?
Some moister should pas through the surface correct? Any suggestions or product that will not kill me
when applying?

I may place stud walls, paint, stain, or tile selected areas. Anyone know the correct surface prep and sealing recamendations. I’m a designer- so not a normal homeowner. Looking for the correct way to handle the cement floors. Thanks JS

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Replies

  1. MICHAEL CHANDLER | | #1

    The dusting you are seeing is probably efflorescence from the drying of the slab. once the area above the vapor barrier has dried that should stop. At that point I would use an acid stripper and a buffer with a black stripping pad to pull off the efflorescence and then hit it with an acid neutralizer (mop and squeegee) followed by a sealer such as Buckeye Cirene http://www.buckeyeinternational.com/products/floorfinishes/cirene/index.html which we have used with pretty good success except that leaving masking tape down on it for prolonged time seems to leave a mark, so pull up the tape after two or three days and you'll be fine.

    Buckeye now makes a Zinc-free sealer they call Verde http://www.buckeyeinternational.com/products/floorfinishes/verde/index.html but the counter guy at the industrial supply house where I buy it says that it is much less durable than the Cirene and I'm not sure I understand what the problem is with zinc in a water based floor sealer so I have stuck with the old stuff. the place that sells the Buckeye products will be able to set you up with the acid stripper and neutralizer, doesn't take very much. renting a 14" buffer will be worthwhile when it comes to pulling up that efflorescence and you'll want a good floor squeegee threaded for a broom handle and a wet vac with a brand new squeegee type floor nozzle to pull up the puddles as you corral the surface water. the floor will breath very well through the finish in BOTH directions. On a rainy day it is possible to get condensation below the surface of the slab! It's quite disturbing to see but very rare and dries up fast.

    I'm sure there are a lot of other approaches and there's nothing magical about this one except that it's the best I've found. I have definitely not had great success with Kemiko concrete floor wax (struggle to get it to spread on smoothly, ended up using an electric buffer and lacquor thinner to buff it out on one job... a bit nerve wracking) or urethane floor finishes intended for wood floors (moisture can get under them and push them off the concrete.) That said, on SOME jobs I have had good success with both the Kemiko and the urethanes but not every job, whereas the issues I've had with the Cirene-type finishes have been much less but it could still be better. (that masking tape thing and spilled peanut butter or massage oil can leave a mark)

  2. Riversong | | #2

    John,

    Where is the vapor barrier in relation to the sand layer and the slab? Sand is a poor substrate for a concrete slab as it becomes a water reservoir. If it's above the VB, then you're putting moisture into the slab every time it rains and the ground gets wet. Efflorescence is generally caused by "rising damp", or moisture rising by capillary action through cementitious or masonry materials, and carrying dissolved salts which are left behind at the surface during evaporation.

    This is an indication that you have created a reservoir below and in contact with the slab. Not much you can do now to correct that other than excavate outside the foundation and install a good perimeter drain. The best base for any slab is 3/4" washed crushed stone, which acts as a capillary break and is also a good medium for a radon vent (which should be below every new slab).

    The best penetrating breatheable concrete and masonry sealers are made from siloxane and silane. Nothing else comes close.

  3. MICHAEL CHANDLER | | #3

    Robert
    Do you have a preferred brand for the sealer you would recommend for a radiant finished stained concrete floor? As I mentioned in my post I'm not really satisfied with the Cirene finish.

  4. MPdjjBwcfD | | #4

    The plastic sheet of vapor barrier is over the compacted sand. So that should be correct.
    Off course the cement contractor did not think I needed gravel? Typical contractor in our society.
    I simply first need to seal the surface ..before I stud wall and finish parts of the rooms.
    How much of the typical surface dusting (laitance) do I need to remove? I'm told this is typical and normal for new cement. One side of two pours seems better. I was told probably had less chlorine added for dying time.
    Will vacuming be enough prep?
    I can't imagine people in a residential house having there cement surface ground down just to seal it?
    Maybe I should just paint.?

  5. Riversong | | #5

    Michael,

    I don't have a recommendation - wish I did. My last radiant slab was covered with a curing sealer by the contractor and I wasn't happy with the high gloss and significant color deepening (turned a rose concrete into brown).

  6. MICHAEL CHANDLER | | #6

    Robert

    Here's a product that looks promising, http://www.bestmaterials.com/detail.aspx?ID=16699

    BASF Enviroseal 20 concrete sealer, 20% silene, water/ethanol solvent
    For a problem floor that needs sealing against water, efflorescence and soil gas there is A-tech Hydra-Block (might be a good thing for the person building near the super-fund site) but it's a sodium silicate acid product and would discolor any wood or metal it came near (like the acid stains for concrete) and also needs the 28 day curing time so can be an issue indoors.

  7. Richard Ugarte | | #7

    Robert,

    You wrote: "The best base for any slab is 3/4" washed crushed stone"

    I'm used to seeing 3-4" crushed stone required under the slab. Is 3/4" sufficient? Or by 3/4 do you mean 3 or 4, and not 0.75" as I read it ?

    There was a question a few days ago by someone thinking of using something like enkamat (a drainage/radon vent mat) in a retrofit basement, trying to get by on minimum digging, but unfortunately no one has responded. This might answer him too.

  8. Riversong | | #8

    Richard,

    Thats 3/4" as in 0.75" screened, washed, crushed stone.

    That's more than coarse enough for good drainage, ventilation and capillary break. It's sharp-edged for good load-bearing and stability. It's washed of fines to prevent clogging of radon or sub-surface drainpipes. And it's small enough to be relatively easy to rake smooth and level.

    3"-4" stone is what I use for a rubble-trench foundation or roadbed, never under a slab or for backfill.

  9. Riversong | | #9

    Clarification:

    That's 4" thickness of 3/4" crushed stone.

  10. MICHAEL CHANDLER | | #10

    As to the enkamat question I think you would need to bring in a soil engineer to answer that one specifically for the soil condition at that site but in the application under an existing house that was mentioned I think it would probably work and certainly worth the modest expense of bringing in the engineer to find out. .

  11. user-716970 | | #11

    Just discovering the Alt codes...The Alt key code for ¾ is 0190...

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