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Understanding Hydrostatic Pressure

When water saturates poorly-drained soil, it creates hydrostatic pressure, which pushes against your foundation walls and leads to structural damage.

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Hydrostatic pressure is a phenomenon that has a damaging effect on your foundation walls and the basement. Over time, it can cause your basement walls to bow or crack, allowing water to enter your home. Buildings and homes that sit close to a temporary water table are the most vulnerable. 

Let’s shed light on hydrostatic pressure, a common and often misunderstood water-related foundation issue, and show you how to deal with it. 

What Is Hydrostatic Pressure? 

Hydrostatic pressure refers to the force that stagnant water exerts on objects that obstruct it or lie in its way. It could be a concrete slab that contractors install below the ground’s water table or a foundation wall that supports your home. 

The more the soil gets wet, the more pressure it will exert on your walls. The water buildup can lead to a host of structural issues. In extreme cases, this pressure can cause your walls to collapse.  

Upward water pressure also dissolves concrete salts and becomes alkaline. It’s this alkalinity that causes the concrete to lose its binding properties. This creates more cracks and pores in your foundation and causes your concrete floors to degenerate.   

Causes of Hydrostatic Pressure 

Soil saturation may be the leading cause of hydrostatic pressure, but it is not the only enabler. 

  • Poor water drainage: Damaged sprinklers, city mains, plumbing, and other water supply lines can saturate the soil in your yard leading to hydrostatic pressure.  
  • Improperly dried concrete: Applying surface membranes before the slab dries up completely can also cause moisture to accumulate on your concrete slab.  
  • Inadequate installation: Sometimes, less experienced flooring and concrete professionals fail to survey the construction site or use vapor barriers with low permeability ratings. Geotechnical surveyors may also forget to locate nearby water sources. All these will propagate soil water and hydrostatic pressure.  

Determining Hydrostatic Pressure 

An easy way to determine the amount of hydrostatic pressure beneath your foundation is by drilling a hole on your concrete foundation’s surface. Wait a day or two to see if the concrete grows dark. You can also test hydrostatic pressure by placing a plastic sheet over your basement floor. Hold the sheet down using duct tape and wait a day or two to see if water droplets form on top of it.  

Concrete epoxy moisture meters will also come in handy in testing hydrostatic pressure. If the moisture content is above 5%, your foundation is at risk for moisture issues.  

The calcium chloride moisture test is another great way to measure hydrostatic pressure. This test measures the rate of moisture emission over 1,000 square feet of space within 24 hours. However, this test is not recommended for lightweight concrete since it is easily affected by ambient conditions, giving you misleading results. A more effective approach is the relative humidity test, which measures moisture deep in a concrete slab.  

How to Fix Hydrostatic Pressure 

Water is a dense liquid that weighs about 60 pounds per cubic foot. Whenever it rains, hydrostatic pressure can build up into thousands of pounds. Such extreme pressure has the potential to damage your foundation walls. To avert these problems, you have to control hydrostatic pressure by eliminating water sources near your home. 

Pressure Relief 

You can reduce hydrostatic pressure around your foundation by diverting water away from it. If you have poorly draining soils, consider installing a sheet drainage material on the ground. This enhances water movement to the foundation drain, significantly reducing the amount of water that pushes against your walls.  

Internal drainage systems provide another effective way to relieve hydrostatic pressure in the ground surrounding your foundation. Have a contractor set up an internal drainage system like BasementGutter™. This device will collect any leaking water and direct it to a sump pump before it has a chance to turn your basement floor into a waterpark.  

Grading your yard or lawn is another effective method of reducing hydrostatic pressure in the soils around your home. What this does is enable water to flow out and away from your home’s perimeter. 

Your gutters and downspouts need to be in good shape to drain water away from the roof. Make sure they’re clog-free and fastened properly. Otherwise, water will pour down the sides of the walls and collect around your foundation. 

Other Waterproofing Options 

Once you grade your yard and implement other exterior drainage measures, you will also need to consider additional waterproofing solutions that can help you keep water out of your foundation. One of these is installing a waterproof barrier between the foundation’s slab or wall and the water source. Such a barrier will stop water from poorly drained soils or a high water table from infiltrating your walls. 

Do you have leaking foundation walls? Contact Foundation Recovery Systems today to schedule a free inspection and repair quote. Our skilled technicians can identify the cause of dampness and recommend a lasting solution.