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Phil, Mechanical Engineer
Category: Home Improvement
Satisfied Customers: 8698
Experience:  Retired contractor, 51 years experience
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Hello. I have a problem in the Crawl Space under my house.

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Hello. I have a problem in the Crawl Space under my house. There is an outdoor drain pipe that starts in my driveway, goes through the opening in the foundation and finally joins the main drain pipes outdoors to the city sewage system. It appears that the area around the opening for the drainpipe through the foundation has eroded and water spews to the area below which in turn has created an opening below the foundation. Can you suggest a do-it-yourself solution and what I am up against to repair the damages? I will attach a photo for you reference. Thank you.

Welcome to Just Answer!

Thanks for the great picture, can you describe the black looking sludge on the floor, does it seem more like algae, sewage, or something else.

So far it looks like ground water leaking through the hole in the foundation...

Is the pipe shown in the picture, black ABS plastic or copper?

Is the piped slopped down from the foundation wall to the main sewer line under the house? Do you know where it comes from and what drains into it.

What is the water table in your area, is it in the deep south, Louisiana for example? or in some parts of Texas around Houston?

We can go from there.

Customer: replied 4 years ago.

The black looking sludge appears to be a mixture of sand, soil and sediment of some kind which is dry at the moment. The black pipe is ABS (PVC?) plastic. The drain pipe originates from a drain opening in the driveway, goes through the opening in the foundation and I believe ends up into the city drainage. Several drainage pipes from the sinks, showers and bathtubs join into this pipe. I am not sure if the toilets share this drain pipe or go another route which I have not checked yet. I am in the Seattle-Everett area in the state of Washington where we usually get a lot of rain during the Fall and Spring months.

Hello again,

Its ABS pipe, real tough material not at all prone to cracking... PVC is a bit more brittle.
Chances are in the 99% range that it is ground water leaking though the hole in the foundation that ABS runs through.

You can buy some 'hydraulic cement' at any large hardware store. Clean out the opening as far back as possible using a coat hanger wire and brush... then mix up the hydraulic cement in a small batch, fairly stiff, and poke it deep into the hole... it expands when it dries

If that stops the leak, go back a few days later and mix up a larger batch and fill in the rest of the hole.

If that only slows the water leak. apply a thick coating of silicone seal around just the very edges of the hydraulic cement... leave the middle of the hydraulic patch alone.


be sure the area is dry before you use the silicone seal.

then wait 3 hours and pack the rest of the hole full of a stiff mix of hydraulic cement.

Work fast, it cures in 5 minutes or so.

Stay in touch as necessary. If you rate my advice so far positively I will hold the question open for unlimited follow up as you might need it days or months from now.


Phil and other Home Improvement Specialists are ready to help you
Customer: replied 4 years ago.

Thanks for your reply with steps to seal the opening. What should I do with the area below where the water will usually sit after some heavy rain? Should I fill the area with soil, cement or other material to build the area up again? I concerned that water could seep through under the foundation.

Hello again,

When you mix the hydraulic cement (it expands when it cures unlike regular cement) mix it real stiff so it doesn't sag away from the pipe when you stuff it into the hole. then expect it set up in 2 to 5 minutes... small batches and working real fast is the way to do it.

If the bottom space does not have a cement floor, now would be a good time to put one in.

Clean the edges of the foundation very well, so the cement floor sticks to it... Hydraulic cement is a good idea for the floor as well.

Thanks for the positive rating!