"Trench warfare" vs. water in basement?
April 8, 2014 2:09 PM   Subscribe

Before we bought our house, our home inspector suggested a solution to a minor water issue in the basement. I'm considering his solution and others, and welcome knowledgeable opinions.

The house is on a hillside, and a boulder (~3 feet across) interrupts the foundation at one point and intrudes into the basement. A smaller boulder does the same in one other spot. When it rains heavily, water occasionally trickles into the basement from those two spots. The boulders have been plastered over previous to our ownership, evidently to prevent the trickling (which was unsuccessful). The water is not much, and could probably be controlled by putting down some old towels. We've been basically ignoring the problem, but I'm trying to get everything ship shape around the house and I want to find an appropriate solution.

The home inspector's suggested solution was to rent a jackhammer and dig a shallow trench (~1" deep) in the floor around each of the boulders, then run a connecting trench from there to the access pit for the sewer lines, where the water could drain out of the house. On the plus side, this solution would be simple and effective. On the minus side, it would be irreversible, ugly-ish, mildly hazardous (tripping, etc), and possibly overkill. None of the minuses are dealbreakers on their own, but together they've made me pause to consider.

The other solutions I've found on the internet include painting the foundation on the inside with special sealant (which looks ineffective), and excavating and coating the foundation from the outside (prohibitively expensive right now, and maybe impossible due to the aforementioned boulders).

What should I do? The ideal solution is cheap, easy, elegant, and will make me look like a genius when I tell my wife about it. Thanks in advance for your help.
posted by sleevener to Home & Garden (12 answers total) 3 users marked this as a favorite
It's not clear if your home inspector was suggesting that the water drain directly into the sewer line. In any case, I immediately had questions about code violations. Not sure if contacting a contractor will make you look like a genius (although it will if it keeps you from violating local codes...), but I'd contact a contractor. This may call for a sump pump.
posted by thomas j wise at 2:35 PM on April 8, 2014

A jackhammer could very easily break up much more than a 1" channel, and would leave a rocky bottom where water would pool in low spots. To do controlled cutting to make a smooth-bottomed channel, you're looking at abrasive grinding tools. Still not expensive, but a very dusty process.
posted by jon1270 at 2:35 PM on April 8, 2014 [2 favorites]

You may want to know how thick your slab is too. Basement floors are often not that thick. There may not be enough material to cut channels without penetrating or cracking the slab.
posted by bonehead at 2:39 PM on April 8, 2014

The trench is a good & effective solution, and you don't need to leave the trench exposed. You should install a french drain in it around the base of the boulders, then a connecting pipe to the sewer exit, and then backfill everything so that it looks like nothing happened (including fresh cement).

The trench area around the boulders will need to remain exposed w/a gravel top so that water can drain into it, but that can be made level so it's not a tripping hazard. You could even install drain covers over that part.

This "trench" should be a cut through the depth of the cement floor, into the substrate, so probably 1ft deep. The drain should have a decent slope to avoid pooling, 1/4" drop per foot, IIRC. You'll have to haul out the gravel/cement/dirt that's displaced by the french drain and pipe. Then haul cement back in (or mix it down there, wear a mask!) to cover the drain pipe when you're done.

Is this a finished basement or more like a root cellar? The bigger worry is moisture management, but it sounds like that hasn't been a problem yet, so I wouldn't worry.

You're correct that most of the "paint on sealants" that are applied from the inside won't work very well. There are more permanent "spray on cement" solutions that may work. Water can have an amazing amount of pressure when pushing into something, and it's very patient.
posted by jpeacock at 2:39 PM on April 8, 2014 [1 favorite]

(basically, this is very similar to installing plumbing in the basement for a toilet or sink - cut the floor, install drains, patch the floor)
posted by jpeacock at 2:40 PM on April 8, 2014

We repaired a flooding basement by having urethane injected into the cracked joint between two segments of the foundation; it's held up quite well in the two years since we've done it. This is different from the paint-on sealants: the contractors drilled the crack a bit wider and pumped (a surprising amount of) urethane in to fill the whole gap; it dried to a dark, almost glass-like appearance.

Since you already know the source(s) of your leaks, that would probably be a whole lot less expensive and complicated than the trench-drain idea. In theory you could DIY it but it looked like a rather involved process, personally I'd hire a professional to do it. (link is a random google, not certain it's the same stuff we used; if you search for "urethane injection" you'll find lots of info)
posted by ook at 3:01 PM on April 8, 2014

Response by poster: Thanks for the answers so far. To address (and add) questions:

It's not clear if your home inspector was suggesting that the water drain directly into the sewer line. In any case, I immediately had questions about code violations.

No, not directly into the sewer line, just into the access pit, which is plain old dirt. Was there anything specific you had in mind, in terms of code violations?

You should install a french drain in it around the base of the boulders, then a connecting pipe to the sewer exit...

This "trench" should be a cut through the depth of the cement floor, into the substrate...

Now that you say that, I'm wondering what's the need for the drain pipe at all, if the french drain drains all the way to the substrate just like the sewer exit pit would?
posted by sleevener at 3:14 PM on April 8, 2014

Having known someone with this exact problem, I can tell you that he tried everything short of digging a full french drain around his foundation, including attempts to deal with the water once it was in the basement, but said french drain was the only thing that ended up really fixing it. His situation was slightly worse than yours in that the water "seeping" around the boulder wasn't seeping at all and was in fact spraying in jets when it rained.

Digging the french drain does not involve any work in the basement, it is (or can be) all outside.
posted by wierdo at 4:13 PM on April 8, 2014

My parents' house had a ~1 inch wide by ~1 inch deep trench running past leaky areas to a sump pump. Seems fine, depending on the flow rate.

Probably cut with a concrete saw, not a jackhammer.

The only thing that worries me is that flowing water tends to cut channels and the flow rate increases over time.
posted by flimflam at 4:52 PM on April 8, 2014

An internal perimeter drain is a legit approach to water management in a basement. Other approaches can work, too.
posted by Monday, stony Monday at 6:56 PM on April 8, 2014

I have read in numerous articles that a trench on the high side of the house (outside, of course), six feet out and two feet deep, lined with gravel, into which a perforated, drain-cloth wrapped PVC pipe is placed (which is then buried and the pipe ran to a drainage area like the street) actually cures the problem completely for many people.
posted by brownrd at 8:09 PM on April 8, 2014

I've also been looking at a similar problem in my house's basement. Something I saw recently on This Old House's episode on a dry basement looks promising as an interior applied material. Kryton is the product they used (I have no affiliation and haven't used it myself, but am intrigued). I think it's also very important to consider exterior drainage issues, things like gutters, a good slope away from the foundation and potentially an exterior french drain, are often doable without digging up the whole foundation.
posted by pappy at 8:14 AM on April 9, 2014

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