Basement Waterproofing Hazards

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Clay Bowl Effect – Myth or Fact?

Clay Bowl Effect DrawingCompanies like AquaGuard Waterproofing Corporation that sell indoor perimeter drainage systems may use the concept of a clay bowl effect when trying to convince you to buy their services.  Where is the Science?  What is this clay bowl effect?  AquaGuard Waterproofing Corporation sales representative drew the picture above when “explaining” the source of water seepage in my basement.  I bought this concept and that was my mistake as the real source of the waterseepage was simply the surface water sliding along the foundation through cracks between the walks around the house and the exterior foundation.  In other words, even if they hadn’t totally messed up the perimeter drainage installation itself, it was the wrong answer to the water seepage problems in my basement.  Again, I bought it so my bad.

Note that it isn’t simply a matter of whether the soil around the foundation is more porous than the undisturbed soil. The real question is how does the water reach the basement walls from the outside?  If the water from the surface can be directed away from the foundation by a substantial distance, say 10 to 15 feet, then it will have little opportunity to flow toward the foundation.  The first line of defense against surface water is proper drainage away from the foundation.

This was certainly the case for my house, though the AquaGuard Waterproofing Corporation sales representative dismissed that source out of hand.  His explanation was the following.  It wasn’t a surface water problem at all!  The real problem, according to him, was the ground water flowing from around the yard would pool into the clay bowl and seep into the basement where the walls joined the floor.  When I told him that I usually saw the water entering from the walls and then flowing to the floor, he stated that was due to the rising water in the clay bowl finding its way into the cracks several feet above the floor.  At the time I gave it no particular thought, he was the so-called “Senior Inspector” for AquaGuard.  Only later did I realize that his explanation was suspect and quite possibly self-serving.  Any difference in the height of the water and the Clay Bowl and the surrounding soil will tend to push the water to whichever side is lower.  Of course since there isn’t any significant amount of water in the basement (one would hope) the hydrostatic pressure from the outside will force the water against the wall and, if cracks are present, into the basement.  The question is simply this:  Is there really a significant level of water building up in the so-called Clay Bowl at all?  Or is the water penetrating the soil also simply flowing along the basement wall and finding its way into the house?

I indicated above that in the case of my house the Clay Bowl Effect explanation was suspect.   How do I know this?  Because after I had the trench path opened up I got to observe what happened when a very heavy rainfall occurred.  We received over 5 inches of rain from the remnants of tropical storm Sandy but the basement remained dry.  More importantly the trench path was dry.  The ground water effect was bogus.  Under normal circumstances the water would have flowed along the surface, down (not up) the walls and penetrating wherever it found a crack.  Fortunately the contractor I had come in and remove the tar not only patch the numerous cracks in the foundation (the real entry point for the water) but they also did an excellent job caulking the walks along side the foundation.  This is a temporary patch, as I still need to grade the surface so water flows away, but it was a great demonstration that the real problem wasn’t what AquaGuard sold me at all.

But I digress.

I want to dedicate this post to exploring where this concept came from and what validity it has, if any.   If you search on-line you’ll find waterproofing companies explaining seepage using the “science” of the Clay Bowl Effect.  Really?  I’ve yet to find an actual scientific article on this, but I’ll keep looking.  More to follow!

18 comments on “Clay Bowl Effect – Myth or Fact?

  1. Steph
    March 27, 2013

    Wow, this is useful to know! Thanks for the post

    • Russ R
      April 6, 2013

      There’s an ongoing arguement in the basement waterproofing industry between those who are proponents of the interior drainage system and those who believe the solution if an exterior barrier. Interestingly the “interior” proponents claim their approach is superior, largely on the fact that it is cheaper. In the case of AquaGuard Waterproofing Corporation, cheaper is hammered home by grossly exagerating the cost of the exterior system (see $35 – $50K hand-written estimate in the figure above) and then presenting their interior system at a small fraction of that cost. The real situation is much more complex. I’ll be posting a report, or a site where it can be found, from the Extension Service of the University of Minnessota that goes into the various problems and solutions in detail. For now I’ll simply summarize with two points: 1). The exterior approach is, in this report, the best solution if you can’t solve the problem by surface grading and redirection of water and 2). The interior approach is discussed but it has shortcomings such as it’s inability to address rising ground water under the floor.

      • Billal
        June 14, 2013

        Home renovation is a great idea that makes a home more aivtacttre, but before home renovation we should consider some significant factors like the development planning, materials needed, total cost including materials and labor.

      • Russ R
        June 14, 2013

        Hi Billal. Thank you for your comments. My experiences go well beyond the factors you list. I would add one needs to dig deeper into the “credentials” of the company you are working with, don’t ignore “warning signs”, and keep an eye (to the extent you can) one what they are doing. Our trust left us vulnerable and we paid the price of being naive.

      • Viraj
        June 16, 2013

        I simply wnaetd to thank you again for this amazing web-site you have designed here. It really is full of useful tips for those who are definitely interested in this specific subject, especially this very post. Your all so sweet plus thoughtful of others as well as reading your blog posts is a great delight with me. And such a generous surprise! Mary and I usually have fun making use of your points in what we should do next week. Our collection of ideas is a mile long which means that your tips are going to be put to good use.

      • Russ R
        June 17, 2013

        Hi Viraj, and best to Mary!
        Thank you for the kind comments on my blog. I’ve been trying to understand both the origin and the factual basis for the so-called Clay Bowl effect. Physically it is believable but I’m less certain about some of the claims that go along with it, and therein lies the problem. For example I heard it claimed that not only does the water flow in and at a faster rate (meaning the porosity of the fill earth is greater than the surrounding “virgin” clay) but the water also pools up, essentially filling the bowl. Now I’m not expert in Hydrogeology or whatever field of engineering and/or science that addresses water flow through the earth but I do know something about Physics and I find it unlikely that the ground water not only flows to the “bowl” but also pools up there to any significant height above the surrounding ground water. The reason is simple enough; the hydrostatic pressure is a function of the difference in water height so, I would reason, if that height get’s much out of balance, the pressure within the “bowl” will overcome the difference in porosity. What would that water difference be for equilibrium, or even a quasi-static condition? Must be a function of the relative porosity of the fill earth around the house and the virgin land. I need to add this into the blog and maybe get some feedback from people with more background in this area. Regardless, thanks again for the nice comments and I hope you find future postings as interesting.

  2. Asha
    June 13, 2013

    This design is wiekcd! You definitely know how to keep a reader amused. Between your wit and your videos, I was almost moved to start my own blog (well, almost HaHa!) Great job. I really loved what you had to say, and more than that, how you presented it. Too cool!

    • Russ R
      June 14, 2013

      My firm belief is that reputable contractors have nothing to fear when educated consumers make informed decisions. I hope to reach as many people as possible; consumers, contractors, our elected officials and those in our government responsible for enforcing the “rules”. However, the information has to be out there and people must find it and take the time to read it. I’ve worked hard to produce an enjoyable and informative site and I really appreciate your feedback Asha! Please spread the word as this goes way beyond my particular experiences, i.e., much of what I’ve experienced is the business model for a number of people and organizations. This little warning may give us all (consumers, contractors, everyone) reason to pause and avoid bad choices.

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  5. Gracie
    July 17, 2014

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  9. ameador1
    September 25, 2014

    I wanted to make a comment – not to argue – but to bring up an idea. I would think the possibility of a “Clay Bowl Effect” could make total sense – in the right circumstance. That being – if the foundation is actually dug into a clay layer or in a larger clay layer outside of the immediate footer excavation. I have done a bit of research on building small ponds and using clay seems to be a common approach to sealing the bottom and sides of the pond to stop the water from leaking out via percolation into more porous soil surrounding the site. It doesn’t even take a thick layer – only a couple, to a few, inches. A pond’s clay lining would definitely have quite a lot of pressure on it – yet they hold the water quite well, including around some drainage systems which exit below the water surface.

    I am digging footers right now to build an addition to our house. The excavation is almost entirely through a little soil, a lot of shale, and some sandstone. I did hit one little patch of clay. The base right now is a little uneven with highs and lows. We had a small rain the other day, about 0.4 inches, and a little of the loose clay (from digging in that spot) ‘dissolved’ in the rain water and flowed into one of the low spots right by it. This low spot is shale and all of the shale areas around it drained immediately, but this little, now ‘clay lined’, low spot has held that water for days now (it’s in the shade) with only a very thin (maybe 1/8″ or so) layer of clay in it.

    The point is, clay can seal very well with the ability to hold water fine – but there must be clay of that nature in your foundation’s surrounding area. You would be talking about a thick, fairly pure layer of clay to have a consistent clay enclosure, but I have seen places like that. My thought is that this kind of effect can happen – but only in the right circumstance – and I’d think without doing a test dig or core sampling and thoroughly eliminating all other options (like in your case – where water was obviously coming in from other means) you could not make this claim as the cause of water issues.

    If the foundation was set in a large clay formation, the walls would have had to have been built extra tough with reinforcing columns/walls, etc… to keep the clay from pushing the walls in over time – as it has a tendency to ‘flow’ when it gets moist or wet (like a cooling lava flow). I have seen it completely blow out concrete block walls in a matter of days. This kind of extra-reinforced foundation wall might be a clue – but I assume you don’t have that.

    Just a though from the description of the “Clay Bowl Effect” and applying some pond and clay theory! 😉

  10. John
    March 1, 2015

    Hi. I would like to suggest you read the University of Minnesota hydrology study on residential homes, surface water, and ground water. Surface grading is always the first step. However many of your conclusions and theories are flawed based on hydrology and hydrostatic pressure. Good luck!

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  12. Padraig in Colorado
    July 27, 2017

    A link to that article would be helpful. I’ve searched and cannot find an article with a title by that name. I found something from Indian Univ that studies contamination and natural resource damage, but nothing on residential homes. Something like that would almost certainly be a region based study, since groundwater will interact differently in different soil conditions. That being said, it would be nice to determine where and how groundwater affects residential homes and how to mitigate those effects. Thank you.

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