Understanding the Risks of Hydrostatic Pressure in Concrete Slabs

Hydrostatic pressure is a term that often gets misused in the construction industry—especially when discussing moisture-related flooring failures. While contractors, builders, and flooring installers frequently cite hydrostatic pressure as a major cause of flooring issues, the reality is that it is far less common than you might think.

So, what’s really happening? More often than not, the bigger threat comes from moisture deep within the slab—not extreme hydrostatic pressure. High relative humidity (RH) levels in concrete can be a silent culprit, leading to adhesive breakdown, flooring delamination, and costly repairs over time.

In this article, we’ll separate fact from fiction by covering:
✔️ What hydrostatic pressure really is (and when it actually causes problems)
✔️ How RH levels in concrete contribute to flooring failures
✔️ Practical strategies to prevent moisture damage in concrete slabs
✔️ The role of proper RH moisture testing before installing flooring

If you want to protect your concrete floors, subfloors, and adhesives from hidden moisture damage, this guide will help you understand the real risks and how to prevent expensive flooring failures before they start.

Table of Contents

• How Concrete Builds Its Strength
• Hydrostatic Pressure Definition & Meaning
• Hydrostatic Pressure in Concrete Slabs
• Relative Humidity in Concrete

Concrete can be a problem when we do not comprehend the fundamental construction terms related to its installation. Contractors also tend to misuse the term, hydrostatic pressure, to describe the dangers of moisture. High relative humidity (RH) levels and hydrostatic pressure can both ruin floors.

However, contractors overestimate and overuse the words hydrostatic pressure when discussing flooring failures.

How Concrete Builds Its Strength

Concrete starts to form and strengthen after the cement and other ingredients are mixed with the water. Curing leads to a floor whose strength is defined by adequate compressive strength, which is achieved with time, allowing for the chemical reaction called hydration to properly occur.  

Drying allows moisture vapors to migrate to the surface and evaporate from concrete. Having conditions, within the building, that are conducive for concrte drying, helps to expedite the process.

Hydrostatic Pressure Definition and Meaning

Definition: hydrostatic pressure is the pressure exerted by fluids at rest.

When concrete slabs are appropriately installed beneath the ground’s water level, pressure builds against the walls of the slab. That pressure, as with any pressure, can accumulate over time. In very rare cases, it is possible that hydrostatic pressure can actually pierce a concrete wall.

The mind conjures spectacular imagery of a seemingly impenetrable concrete basement blowing out, leaving water-logged carnage in its wake.  This happens, in its truest form, much less frequently than people use the term.

Free Download – 4 Reasons Why Your Concrete Is Taking Forever to Dry

Hydrostatic Pressure in Concrete Slabs

Hydrostatic pressure in concrete slabs is a critical factor that can lead to various issues if not adequately addressed. It refers to the pressure exerted by fluids at rest, such as water, against the walls of the concrete slab.

Hydrostatic pressure can build up over time when a concrete slab is installed below the water level.

If the hydrostatic pressure becomes too high, it can pose significant risks to the integrity and performance of the concrete slab.

In rare cases, the pressure can even cause the concrete wall to rupture, resulting in water damage and structural issues.

To prevent the harmful effects of hydrostatic pressure, it is essential to take appropriate measures during the construction and installation of concrete slabs.

Here are some key considerations:

• 1. Waterproofing:

Proper waterproofing techniques should be employed to create a barrier between the concrete slab and the surrounding water. This can include waterproof membranes, sealants, and drainage systems.

• 2. Drainage:

Adequate drainage systems should be in place to redirect water away from the concrete slab. This can help alleviate the buildup of hydrostatic pressure and prevent water from seeping into the slab.

• 3. Moisture testing:

Regular moisture testing should be conducted to monitor the moisture levels within the concrete slab. This can be done using moisture meters or in-situ probes to measure the relative humidity (RH) levels. Ensuring that the moisture levels are within the recommended range for flooring installation is crucial.

• 4. Drying time:

Sufficient drying time should be allowed for the concrete slab before installing flooring materials. This enables moisture vapors to migrate to the surface and evaporate, reducing the risk of ongoing moisture-related problems and flooring failure.

By understanding and addressing the dangers of hydrostatic pressure in concrete slabs, contractors can ensure the longevity and performance of the structures they build.

Following industry best practices and consulting with experts when dealing with hydrostatic pressure issues is crucial to mitigate any potential risks.

Relative Humidity in Concrete

Successful building contractors recognize the immense value of quality workmanship at each stage of installation. Concrete needs to set, it needs to breathe.

Installers need to ensure the completion of both disparate processes by continuously measuring the RH levels, in the slab until the slab has reached the finished flooring and/or adhesive manufacturer’s recommendations for appropriate moisture levels. Failure to allow the slab to properly and adequately dry can lead to ongoing problems and flooring failure.

There is a simple and highly accurate way to determine whether a slab is dry enough for flooring installation: digital concrete moisture meters from Wagner Meters.

Wagner Meters’ Smart Sensors are not only smart because they are cost-effective, but also because they are specifically designed as single-use in-situ probes – customers never have to worry about calibration issues and documentation is a snap with the included NIST-traceable calibration certificate. 

Installers place single-use, factory calibrated probes inside the slab at 40 percent depth. Then, with a simple hand-held device, accurately called the Easy Reader,  measurements of the RH can be regularly taken at probe level for instant feedback of how close (or how far) you are from having the slab dry to an appropriate level for your floor covering installation.

The Rapid RH^® is fast, accurate, and the simplest to comply with ASTM F2170.

Further Reading:

Concrete Foundation Association of America Home Page.

Video: What to do if hydrostatic pressure leaks water into your basement.

Jason Spangler

Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.

Last updated on March 6th, 2025