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wasman · Apr 30, 2009, 08:35 AM

Here is my situation: I have a house on a concrete slab that unfortunately sits right on top of an underground spring (we have several springs on the property). This was discovered by finding 4-6 inches of water throughout the entire finished basement (and destroying everything down there) right after we had a record-breaking all-day rain. The flooding was a result of hydrostatic pressure from the spring and the open dap-out for the tub which spring water was pouring out of. We solved the problem by having a french drain system installed around the entire interior perimeter of the house with a gravity drain going out to the culvert. The workers have to now re-concrete over the trench that they jack-hammered. Ergo the new problem: they say that they have to cover the entire floor with concrete for warranty guarantees – this means also underneath the bathtub, which the french drain system runs under, including the dap-out for the P-trap. Now this goes against everything that I ever learned in that you never, ever cover the dap-out with concrete (only gravel) so it can provide access for future plumbing repairs and other work. The workers state that they have to concrete completely under the tub in order to insure the spring water moves to the edges where the french drain is. So my quandary is: do I fill in the dap-out or not? If not, future spring water may flow out of the open dap-out since it would the path of least resistance resulting again in a flooded basement. Does the open dap-out rule apply to homes with underground springs? If I do fill it in, I complicate future repairs and renovations. Maybe I can cover the dap-out location with only a one-inch layer of concrete so that it will help guide the spring water into the french drain system, and still allow the easier break-out of a thin layer of concrete rather than a typical 3-4 inch thick layer if I ever have to access it. Thoughts? Ideas?

hkstroud · Apr 30, 2009, 08:23 PM

Well, if it is a matter of warranty on their work, I'd let them do it. You didn't say how thick they plan to pour the concrete top coat, but if you ever have to service the tub trap it won't be that difficult to break out around the trap. Ideally you should be able to fill the dap out to near the top of the existing floor with gravel.

wasman · May 1, 2009, 04:37 AM

They are going to do the work and they had planned to simply match it to the same thickness as the rest of the slab (about 3+ inches). I think it's best to have them just load up the dap out with gravel and then apply a thin coat of concrete on top. It would make breaking it out much easier in the future. Many thanks.

speedball1 · May 1, 2009, 06:10 AM

Tub dap-outs are there because the tub drain connects to the trap raiser beneath the floor line. We pour over the shower trap and raiser with no ill effects.

They are going to do the work and they had planned to simply match it to the same thickness as the rest of the slab (about 3+ inches).

If their warranty mandates a full pour I have no problem with that but if it gives you concern then see if filling the hole with gravel with a thin layer of cement on top will void their warranty and go from there. Good luck, Tom

wasman · May 1, 2009, 02:12 PM

I will do that. Thanks all - you have eased my concerns!!

Milo Dolezal · May 2, 2009, 11:14 AM

It is a very unusual situation. I don't even think pouring concrete over the spring will do that much. Constant wetness under the slab will make concrete wet ( high % of moisture ) and that may potentially create other problems...

But as our Experts suggested above: for now, do what they suggest. They are "paying" for it and offer their guarantee...

What I would do in my house: I would simply dig a dry well and put in site pump. Than, it would pump water away from the house using it for irrigation...