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What Is Hydrostatic Pressure?

Groundwater can saturate the soil beneath your foundation and exert hydrostatic pressure on the foundation walls, causing them to crack or bow.

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Hydrostatic pressure acts on your home’s concrete or block foundation. This can lead to water intrusion and a host of other water-related problems. You’re a good candidate for hydrostatic pressure if your home sits close to a temporary water table or soils with high water saturation. We will explain the term hydrostatic pressure, one of the misunderstood foundational issues behind water-related home problems. 

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What Is Hydrostatic Pressure? 

Hydrostatic pressure refers to the outward and downward force that standing water exerts on any surface or object that stands in its way. In your case, it could be the foundation walls or basement walls. This relentless push can lead to structural problems. 

As water percolates and builds up in the ground, it exerts pressure on the soil around your home, which in turn pushes against underlying structures like your home’s foundation. This force is destructive. If the pressure is extreme, it will cause the foundation walls to crack, bow, or collapse. 

Upward moving moisture will also dissolve concrete salts and become alkaline, and this can have a damaging effect on your floor’s coating. Bubbles will form in the coating. When these pop, they will release pressurized chemical mixtures or water. Eventually, the coating will delaminate if the water pressure exceeds the coating’s ability to adhere to the substrate. 

Water roughly weighs 60 pounds per cubic foot. At any moment, there could be several thousand pounds of hydrostatic pressure pushing hard against the foundation walls. Such extreme pressure causes water to permeate into the foundation. Even a solid foundation cannot withstand such tremendous pressure. That’s why it’s extremely important to take preventive measures to stop water infiltration. 

What Can Cause Hydrostatic Pressure? 

Soil saturation is the leading cause of water intrusion. However, it’s not the only cause. Applying surface membranes before they dry up completely and excessing troweling are other factors, and these cause moisture to accumulate on a concrete slab. Less experienced floor installers can also cause hydrostatic problems when they fail to perform sufficient onsite evaluation or use vapor barriers with low permeability. Sometimes, geologists surveying the area fail to pick up on natural water sources nearby. 

Detecting Hydrostatic Pressure 

The simplest way of testing for hydrostatic pressure is to create a hole on your concrete foundation and wait to see if it will grow dark. Another method is to hold a plastic sheet down with duct tape and see if water droplets will build up on top of it. 

You can also get a moisture meter and use it to measure moisture content. If the moisture concentration is higher than five percent, your foundation is at risk of hydrostatic issues. 

The calcium chloride (CaCl) test is another surface-based evaluation of concrete moisture. What this test does is measure the emission rate of moisture over 1,000 sq. ft of space within a 24-hour window. 

However, ASTM International doesn’t recommend this for lightweight concrete. 

A much better method is the relative humidity (RH) test, which uses a probe to measure the moisture concentration deep in the foundation slab. 

Solutions 

While there are many solutions to control hydrostatic pressure, the best way to control it is to stop water from infiltrating the concrete. You can do this by installing a waterproof barrier between the concrete slab or wall and the water source.  A water barrier stops the foundation from absorbing ground moisture from a high water table or poorly drained backfill via capillary action. 

To reduce hydrostatic pressure in poorly draining soils, install sheet drainage material. What this does is enhance water movement to the foundation drain and reduce pressure on the outside of the walls. 

In poorly-draining soils, sheet drainage material can be used to enhance the movement of water to the foundation drain and reduce hydrostatic pressure against the outside of the wall. 

Alternatively, you can use water-based epoxy systems to deter moisture and overcome hydrostatic pressure. Breathable systems let water through the concrete substrate, preventing the floors from cracking or bubbling. 

Another thing you can do to stop water saturation is appropriate grading. This approach ensures water is dispersed slowly over the landscape. This will keep hydrostatic pressure low. 

Fixing your guttering system and ensuring downspouts channel water away from your home’s foundation also helps prevent water from saturating the soil. 

You can also relieve hydrostatic pressure by setting up an interior drainage system. The good thing about this system is it ejects water before it collects and rises over the basement floor. This way, hydrostatic pressure won’t act on the concrete. 

If you’d like to restore your water-damaged foundation or protect your foundation from hydrostatic pressure, contact the experts at JES Foundation repair for a free foundation inspection and repair quote today.