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Water Seeping Through Foundation Slab: Hydrostatic Pressure & More

Water Seeping Through Foundation Slab_ Hydrostatic Pressure & More
Water Seeping Through Foundation Slab_ Hydrostatic Pressure & More
If water is seeping through your foundation slab, don’t panic! There are several ways you can stop water seepage, including installing a drain tile, sump pump, or French drain. We talk about those solutions, how hydrostatic pressure plays a part in water seepage, and more in this article.

Why Is Water Seeping Through My Foundation Slab?

The main reason water is seeping through your foundation slab is due to hydrostatic pressure. Hydrostatic pressure is when water builds up outside your foundation walls or underneath your foundation slab. Water weighs around 60 pounds per cubic foot. So, if the soil around or under your foundation is saturated with water, there could be tens of thousands of pounds of pressure pushing against your walls or slab.
Concrete is already a porous material. This means that water could find its way through your concrete by itself. But, if you have cracks or cove joints that aren’t sealed properly, water will use those openings to enter your foundation.
Here are a few other places water enters your foundation.
  • Through pipes in your walls or floors – When plumbers install pipes in your foundation, they drill holes slightly larger than the pipes themselves. After the pipes are inserted through the holes, they fill the gaps using hydraulic cement. When that cement breaks down, which it will, outside water can fill the voids and seep into your foundation.
  • Through cove joints – Cove joints are the space between your foundation wall and foundation slab. Without a drain tile system to collect gathering water, moisture can use these openings to enter your foundation.
  • Through foundation cracks – No matter the size, water can use foundation cracks to enter your basement or crawl space.
  • Through degrading concrete – If sections of your foundation slab or walls begin to deteriorate, water can use the openings to enter your foundation. This is also called honeycombing.
  • Over-the-top seepage – Water can enter your basement through the space between your foundation wall and the first floor.
  • Windows and window wells – If your basement egress windows or window wells are not sealed and drained properly, water could seep through any cracks or openings and enter your foundation.
drain tile and sump pump
water in drain tile trench

How Do I Prevent Water From Seeping Through My Foundation Slab?

You can prevent water from seeping through your foundation slab by controlling how much water saturates the soil outside your walls and under your slab.
  • A French drain will collect water in your yard – If water is pooling up in a low part of your yard or near your foundation, the soil will become saturated with moisture and lead to hydrostatic pressure.
  • Gutter extensions will prevent water from pouring too close to your foundation – Your gutters should be dropping water away from your home by at least 20 feet. Otherwise, water can saturate the soil next to your foundation. We also recommend cleaning out your gutters as often as possible to prevent clogs and buildup, which will allow water to pour over the sides.
  • Grading your property will counter poor drainage – If your property is sloped toward your home, water will drain into the soil near your foundation, promoting hydrostatic pressure.
French drain

How Do I Stop Water From Seeping Through My Foundation Slab?

The only way to stop water from coming up through your foundation slab is by installing a drain tile system, vapor barrier, and sump pump.
  • Installing a vapor barrier will counter moisture seepage – A vapor barrier is a thin (10 to 20-mil thick) sheet of polyethylene that’s placed along your foundation walls. This will keep water from seeping through your walls, channeling any collected moisture into a drain tile system below.
  • Installing a drain tile system will counter seeping groundwater – A drain tile system consists of a perforated pipe that’s laid in a bed of washed stone at the base of your foundation walls. This system can be placed either under your slab or outside your foundation walls. Any rising or outside groundwater will seep into the perforated pipe and travel to a sump pump.
  • Installing a sump pump will eject any water – A sump pump is a fixture that sits in a sump pit. Any collected water in your drain tile system will be deposited into the sump pit, and once it reaches a certain level, the pump will activate and eject the water out of your home using discharge lines. The discharge line will transport water far enough from your home, preventing it from gathering near your foundation again.
sump pump with water

Who Can Help In The Greater Chicago Area?

If you live in the Greater Chicago area and have water seeping through your foundation slab, call The Real Seal. We’ll come out and inspect your foundation, pinpointing where water is coming from and come up with the best solution. By combining a drain tile system with a vapor barrier and sump pump, we can effectively waterproof and seal your foundation. Call today for your free inspection and estimate. We also offer foundation repair, crawl space repair, and more!


Austin Werner

Austin Werner is the Owner of The Real Seal LLC, a basement waterproofing and foundation repair company. Austin believes that having a highly trained and happy team is the key to success. This is reflected through hundreds of 5 star customer reviews his company has received online.

18 Responses

  1. Good day
    I have a concrete roof top I need to pour a water base sealant liquid .to follow the seepage track and form a seal
    Do You perhaps have any suggestions
    nb..It seems to acure it the summer heat when expansion take take place Regards

    1. Hi Ernest!

      We don’t do roofing, though an elastomeric waterproofing roofing tar is likely your best bet. I would point you to consult with a roofer to see what they can do.

      1. Hi Bobbie,

        Ernest never replied that he got it taken care of. But what you are looking for is a roofing solution for a concrete flat roof. An elastomeric tar, liners, and insulation tend to be the typical fix. You can also spray expanding foam as an all-in-one solution with the correct contractor as well. It would be best to get a few contractors out there for quotes to get it sealed.

  2. I have a problem in the basement car park where in times of heavy rain, water seeps in to the basement carpark. We have an efficient underground pit with 2 good pumps operating. What is the remedy

    1. Hi Krishn! It’s hard to determine a source of water without a site visit. It is possible you are dealing with Foundation Cracks, Ceiling Cracks, and it is even possible your underground pit is not as efficient as you may think. All these things can be diagnosed with a site visit.

      1. Hi I have foundation slab that is damp from water getting in. The wall is directly under the line separating our driveway and garage floor. The wall is wet but hasn’t gone through the vapour barrier yet. Is this ok?

        1. Hi Robert!

          If you are sitting on a slab with no basement or crawl space that is getting water, the best solution will be to manage the water around the foundation from the outside. Gutter extensions, French Drains, and proper grading of the yard so all water flows away from the foundation is crucial. Did you know that the average roof produces 1,000 gallons of water from a single inch of rain?

          Concrete, brick, and masonry has what is called the “wick effect.” This is where concrete that sits in water can actually pull water up and even deposit it a few feet up in the most extreme situations. If this is happening, the water that is sitting around the foundation must be moved in order to fix it. I hope this helps!

  3. I live/ own a small condo on ground level, about 30 feet from a big Lake. The lake has nothing to do with this situation, but when we get more than one solid day of continuous rain, water comes in my living room at the foundation, (near the baseboards) and spreads all over my tiles unless I stay right there day and night mopping it up and putting towels there; having to wring them out every 5 min. As a senior in my 80s, this is getting a little old and tough for me to handle. Two years ago when this happened they (Board/Mgt) hired a company that dug a trench about one foot down outside my unit and filled it with concrete. I think they tried to put a waterproof substance there before the concrete. IT DID NOT WORK. It is happening again. Please advise with any resolution that might work.

    1. Hi Marry Ann,

      I’m sorry you’re dealing with this. Water situations are always difficult.

      To start, the lake does have an effect on your seepage situation. With the lake there, the water table is high and heavy rain will raise it enough to seep underneath your floor. As you are on a ground floor slab dealing with this, water management of the rain and an exterior French Drain would be your best route to stopping the water seepage.

      How this would work is by digging a trench around the house, but instead of filling it with concrete, you would place a perforated pipe in a bed of gravel in the trench. This would be graded towards the lake and discharge into the lake as well. All of your gutter downspouts should also be put into the pipes, and those pipes should turn from perforated to solid once away from the home.

      In a 1″ rain, the average American Home produces about 900 gallons of water. This is a lot of water to deal with, and if not properly managed, will come into the home. Coupled with a high water table (with the lake so close), water management is essential in your situation to stop the seepage.

      I hope this helps!

  4. We recently had 8” of rain in my area. My carport was enclosed approximately 1980 and converted to a den. After water seeped in a few years later along the front of the house the length of the room, we had someone come, dig down to slab and coat the area with tar. Since that time, water has seeped in 2 times—-just a little bit in the 1990’s which was handled with pulling carpet back, drying all, sanitized and shampooed carpet and put back down. The only other time was the rain of 6 weeks ago. Would a reasonable solution be to dig out and tar the area again or use a rubberized foundation compound, or a different method. Thanks

    1. Hi Martha!

      Many times, it is not enough to just seal your foundation. We highly recommend installing French Drain or Drain Tile around the foundation in that trench as well, directing the water away from the structure.

      Also, you should be looking above the foundation at the siding. Brick and vinyl siding can leak in heavy rain if not properly sealed/tuckpointed regularly. Also window and door flashings, roof issues, and chimney issues can all contribute to seepage of a garage-den conversion. Be sure to get a mason/tuckpointer and roofer out to take a look at all of those areas.

  5. I have a floor drain in my basement that is tied into my French drain that is at the base of my foundation. The system drains into a culvert surrounding my house. When we get a heavy rain, the water level in the culvert is higher than my outlet pipe and water comes up the floor drain and enters the basement.
    When the level in the culvert goes down, then the water drains out and seeps down the concrete floor. All dries up in about a week.
    Will putting in an expansion plug in the floor drain, to prevent water from entering, cause a problem with hydro static pressure building up andt damage the French Drain or my floor?
    I also have a sump pump that runs, but the water drains into the same culvert that is causing the problem.

    1. Hi Kathleen!

      While gravity drain systems that discharge straight into an exterior culvert are appealing because you don’t need a sump pump, this is a common issue with them. While you are not so much likely to have problems in the future with damage to the floor, you will be unable to ever finish the basement as it will always have the potential to flood.

      During resale, the buyers will request (and likely get) a large credit to re-do the system up to code with the proper sump pump system installed. Something to keep in mind, as future buyers will be expecting to be able to use that space, even if you are not.

  6. I have a basement with a sump pump. The only problem I have had in the 20 years I have lived there (new when I moved in) is when the sump pump faed some years ago. Until this last month.

    We had a long period of heavy rain, coupled with a power failure that lasted 6 days so the basement flooded. When we got power ba k the pump emptied the basement nicely, but burned out the pump with constant running, so basement flooded again. I replaced the pump but when it dried out, it left two fairly large areas of pooled water at opposite sides of the long side of the basement, at the same end as the sump pump. Seem to be in the area of where the floor meets the wall but they eventually dried out.
    There are no cracks. We have just had another big storm and although the pump seems to be working those two areas now have pooling water again, which doesn’t floe to the sump pit. What can I do? I’ve spent so much money on this already and can’t afford more.

    1. Hello Aileen,

      I’m sorry to hear you’re having this issue. When you replaced the pump, did you do it yourself? The entire system completely hinges on the sump pump, and if it isn’t adequate, or there isn’t a battery backup system installed, you are going to eventually have trouble regardless. The sump pump needs to be powerful enough to handle the larger storms we get (minimum 1/2 HP for larger basements) as well as have an adequate backup pump (minimum 1/3 hp) in order to keep up with heavy rainfall.

      The pumps sold at big box stores are simply not enough, especially the backup systems. Also, if the basement is original and the drain tile is original, it is possible you have a clay drain tile system. They used to install these before the code changed to make it plastic pipe. These clay pipes deteriorate over time, and when they do, they will need to be replaced. Unfortunately, if this is the case, it will cost some money to install. Many contractors, however, do have financing options to help with the larger cost for those projects.

      But before all that, be sure all of your gutters are buried and extended at least 15-20 feet away from the home. You may just be overloading your system with gutter water, which is common. Hope this helps!

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