Non-Destructive Testing for Vapor Barrier Integrity Using Nitrates

Frederick M Hueston   StoneForensics.com

Non-destructive testing (NDT) plays a crucial role in evaluating the integrity of vapor barriers, particularly in structures like slab-on-grade foundations that are in direct contact with the earth. Vapor barriers are essential in preventing moisture migration from the soil into the concrete, which can lead to various structural issues. The effectiveness of these barriers can be compromised over time due to various factors, making it vital to assess their condition without causing further damage to the structure.

One innovative NDT method for assessing the condition of vapor barriers in concrete slabs is the use of nitrate test kits. This method is based on the principle that concrete itself does not naturally contain nitrates. These compounds are typically present in soil and can permeate into concrete only if there is a breach in the vapor barrier that allows soil contact.

The Nitrate Test Kit Method

Principle:

The presence of nitrates in a concrete slab is an indicator of moisture ingress from the soil.

These compounds are not a part of the concrete mix and only appear when the vapor barrier is compromised.

Procedure:

Sample Collection: Small samples of moisture or efflorescence are collected from different areas of the concrete slab.

Testing: The collected samples are then tested using a nitrite/nitrate test kit. These kits are designed for quick and easy use and provide immediate results.

Interpretation of Results: The presence of nitrates in the samples indicates that moisture has infiltrated the concrete from the soil, suggesting a breach in the vapor barrier.

Advantages:

Non-Destructive: This method does not require drilling or cutting into the concrete, preserving the integrity of the slab.

Rapid and Easy: The test is straightforward and can be performed on-site, providing immediate results.

Cost-Effective: Compared to other methods, nitrate testing is relatively inexpensive.

Complementary Methods

While the nitrite/nitrate test provides valuable insights, it is often used in conjunction with other NDT methods for a comprehensive evaluation. These may include:

Moisture Meters: To measure the level of moisture content in different areas of the slab.

Infrared Thermography: To visually identify moisture patterns and anomalies in the slab.

Ultrasonic Testing: To assess the integrity of the concrete and the vapor barrier.

Limitations and Considerations

Environmental Factors: External factors like recent rainfall can affect moisture levels and should be considered when interpreting results.

Chemical Interferences: The presence of other chemicals in the concrete mix may interfere with the test results.

Experience Required: Proper interpretation of results requires a certain level of expertise.

The use of nitrate test kits for non-destructive testing of vapor barriers in concrete slabs is an effective, efficient, and cost-effective method. It provides a clear indication of the barrier’s integrity, especially in slab-on-grade constructions in contact with the earth. However, for a comprehensive assessment, it is recommended to use this method in combination with other NDT techniques and under the guidance of experienced professionals.