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  1. #1
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    Mar 2011
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    Default Stain and bump on the slab.

    Hello,

    Today I was visiting, not inspecting, a building and I saw 2 interesting things.

    First, I saw some stains on the slab, which do not worry me because some water probably accumulates under the slab. A sump pump should help the situation.

    Second, I noted that the slab was bumping. I thought of pyrite at first, however, the building was constructed in 1954.

    Can anyone tell me more about the bumps and what phenomenon creates them? Any repairs?


    Thank you

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  2. #2
    Join Date
    Feb 2008
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    Default Re: Stain and bump on the slab.

    The first thing that comes to mind when looking at the stain is carpet stains.

    The bumps look like spalling.

    Steven Turetsky, UID #16000002314
    homeinspectionsnewyork.com
    eifsinspectionsnewyork.com

  3. #3
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    Default Re: Stain and bump on the slab.

    Quote Originally Posted by Steven Turetsky View Post
    The first thing that comes to mind when looking at the stain is carpet stains.

    The bumps look like spalling.
    Spalling seems the problem indeed. (I just googled it thank you)

    The carpet is also pretty accurate (didn't think of that one), however, there is supposed to be a second reason for the stains beside the carpet, for example Water infiltration + carpet could be a possibility for the stains or high humidity + carpet could be another possibility, or again, maybe water accumulating under the slab.

    Thank you for the help, that was quite helpful!


  4. #4
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    Default Re: Stain and bump on the slab.

    Why are the walls raised up like that?

    It looks like there were sleepers or joists down with plywood over them, in which case any carpet would have been up on the plywood. That would leave the slab moisture coming up from underneath ... or worse, the slab may be below exterior grade and may be getting wet frequently.

    My guess all comes down to why are the walls up like that is were there sleepers/joist and a plywood floor installed ... if so ... why was it removed?

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  5. #5
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    Default Re: Stain and bump on the slab.

    Expansive clay?
    Expansive Soil Problems and Solutions

    Differential heave of expansive soil is also a common occurrence for pier and beam foundations. The differences in loading are often between interior isolated piers and continuous footings which usually carry heavier loads. As with the slab-on-grade foundation, uniform wetting of foundation soils can result in a mounding pattern where interior floors have heaved more than the building perimeter.



  6. #6
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    Default Re: Stain and bump on the slab.

    Quote Originally Posted by Jerry Peck View Post
    Why are the walls raised up like that?
    Worlds shortest crawlspace.

    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

  7. #7
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    Default Re: Stain and bump on the slab.

    Quote Originally Posted by Rick Cantrell View Post
    Worlds shortest crawlspace.
    I was thinking concrete-lined underfloor plenum, but that creates all kinds of other problems with moisture down there.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  8. #8
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    Default Re: Stain and bump on the slab.

    I came across a situation once where the slap was uplifted due to frost heave during winter construction, prior to house being closed in and heated. Might explain why the sleepers and plywood were installed - to cover the bump and level the floor.


  9. #9
    Join Date
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    Default Re: Stain and bump on the slab.

    Quote Originally Posted by Eli Smith View Post
    Hello,

    Today I was visiting, not inspecting, a building and I saw 2 interesting things.

    First, I saw some stains on the slab, which do not worry me because some water probably accumulates under the slab. A sump pump should help the situation.

    Second, I noted that the slab was bumping. I thought of pyrite at first, however, the building was constructed in 1954.

    Can anyone tell me more about the bumps and what phenomenon creates them? Any repairs?


    Thank you
    Here is one possible cause:

    Alkali-silica reaction in concrete


  10. #10
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    333

    Default Re: Stain and bump on the slab.

    Quote Originally Posted by Mark Reinmiller View Post
    Here is one possible cause:

    Alkali-silica reaction in concrete
    Not likely to be ASR. I've looked at literally hundreds of ASR-damaged structures over the years, and all of them were characterized by considerable map-cracking on the surface. If severe enough, it actually converts the concrete into gravel, rendering it completely dysfunctional.

    I didn't see any such cracking in the OP's pix, and what he called "bumps" actually appears to be a heavy accumulation of efflorescence.


  11. #11
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    Default Re: Stain and bump on the slab.

    Quote Originally Posted by BridgeMan View Post
    I didn't see any such cracking in the OP's pix, and what he called "bumps" actually appears to be a heavy accumulation of efflorescence.
    That's what I think, too.

    And I've never seen walls built like that. We "float" our basement walls, but those aren't floating. Just looks plain weird, but the mice can quickly traverse the room.

    If you choose not to decide, you still have made a choice.

  12. #12
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    Snowbird (this means I'm retired and migrate between locations), FL/MI
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    Default Re: Stain and bump on the slab.

    Quote Originally Posted by Eli Smith View Post
    Hello,Today I was visiting, not inspecting, a building and I saw 2 interesting things. First, I saw some stains on the slab, which do not worry me because some water probably accumulates under the slab. A sump pump should help the situation.Second, I noted that the slab was bumping. I thought of pyrite at first, however, the building was constructed in 1954.Can anyone tell me more about the bumps and what phenomenon creates them? Any repairs? Thank you
    A finishing basement floor installed on sleepers is not that uncommon in the great north. Looks like same has been incompletely removed/demo'd, perhaps having been DIY outfitted originally and without permit.I suspect a packaged spa or hydro tub (or sauna) was set to void in sleeper floor and has been subsequently been removed, which was less-than-idealy maintained and house-kept; and one which had a platform which may have been set/attached to the slab using tapcons, charge loaded fasteners, or similar, demo and restoration as yet incomplete. Oval-like pattern might be from damage to basement slab/subfloor from platform support crib walls or from leaking of recirc system and/or additives to circulating water (cleaning products, bath additives, or for spa water quality products).That's my SWAG for the "other reason" and pattern suggests that the damage cause may be sourced primarily from above.Another SWAG is that the basement sported (perhaps even originally) an imbedded hydronic or electric floor/subfloor comfort radiant heating system, perhaps in floated gypcrete or similar upon the basement "slab" floor which has subseqently failed or been damaged (possibly with addition of sleeper/floor platform and is thus the cause of the pattern & damage (esp if hydronic was pierced) and may also be "why" the platform floor was removed.If carpet tack boards or other was directly fastened to basement slab floor will have eventually corroded not having been imbedded completely in slurry. Basement may have sported numerous floor applications over the decades in various finishing attempts or stages by multiple parties.DSC04545000000.jpg

    Last edited by H.G. Watson, Sr.; 05-25-2013 at 08:04 AM.

  13. #13
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    Southern Vancouver Island
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    Default Re: Stain and bump on the slab.

    2 little pics and a world of speculation.

    The old basement wood floor has been cut away to reveal the original 1954 basement floor. Note the sawdust patterns in pic 1.

    In 1954, the basement was an unfinished pit for the furnace and storage - the floor was not level. There may be an outcrop of bedrock there so the concrete is thinner and humped up along that ridge of bedrock. There is no vapor barrier because it was 1954.
    The thin concrete on bedrock allows moisture to escape more readily and that leaves efflorescence behind. For years, this has all been covered by the plywood floor.
    Chip it down more or less flat and lay a new floor down, and make sure the foundation perimeter drainage is working properly to keep the basement dry.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  14. #14
    Ted Menelly's Avatar
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    Default Re: Stain and bump on the slab.

    Quote Originally Posted by John Kogel View Post
    2 little pics and a world of speculation.

    The old basement wood floor has been cut away to reveal the original 1954 basement floor. Note the sawdust patterns in pic 1.

    In 1954, the basement was an unfinished pit for the furnace and storage - the floor was not level. There may be an outcrop of bedrock there so the concrete is thinner and humped up along that ridge of bedrock. There is no vapor barrier because it was 1954.
    The thin concrete on bedrock allows moisture to escape more readily and that leaves efflorescence behind. For years, this has all been covered by the plywood floor.
    Chip it down more or less flat and lay a new floor down, and make sure the foundation perimeter drainage is working properly to keep the basement dry.
    Even though your answer has a bit of speculation/guessing, it is what I would have speculated/guessed

    Good answer John


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