Non-Destructive Testing in Masonry Investigation

Words: Kate ViennaPhotos: MCAA

One of the greatest deceptions in restoration and building is that the visible symptom is rarely the actual problem. Water may enter through failed flashing 20 feet away from where it finally appears inside the building. A new CMU wall that looks sound as can be may be grouted entirely insufficiently during construction.

Historically, the only way to understand truly hidden conditions was to start taking the building apart. Today, restoration professionals have a growing toolbox of non-destructive testing (NDT) technologies that allow us to investigate existing buildings with far less disruption before determining the appropriate actions.

Investigation Before Demolition
Sometimes invasive measures are simply necessary. Contrary to popular belief, most investigations don't begin with sophisticated equipment. They begin purely with experience and a trained eye. An investigator first studies how the building was designed, how water should move through the wall, how different materials interact, and what the visible symptoms suggest. Only then do we know:

What technology to use.
Where, precisely, to use it.
What we're keeping an eye out for.

Where Is Non-Destructive Technology Used?
Applications can essentially be reduced to two areas: old buildings and new buildings (or buildings-to-be).

Restoration and forensic investigations: Non-destructive testing technology has given restoration specialists the ability to apply what seems like the superpower of X-ray vision to structures to identify cavities, water intrusion, and other concealed conditions. When trying to understand buildings that are both significant and significantly old, this becomes a great tool to find out as much as possible about a structure without having to take anything apart.
New construction: NDT technologies are also being used during active construction as quality assurance tools. These tools verify reinforcement placement, confirm proper grout consolidation within masonry walls, locate embedded components before drilling or anchoring, and identify defects before they are concealed behind finished construction. Detecting these issues early improves quality while helping prevent costly rework and future performance failures.

No single technology provides every answer. Instead, users select different methods depending on the question they're trying to answer and often use multiple technologies together.

Ultrasonic Testing
One of the most useful tools available is Ultrasonic Pulse Velocity (UPV) testing. Two sensors are placed against masonry or concrete. One sends a high-frequency sound wave through the material while the other receives it. Dense, continuous material transmits the wave effectively, while cracking, voids, delamination, or deterioration can slow or disrupt the signal.

To get a clearer idea, investigators can establish a grid across an area and compare numerous measurements, rather than relying on one reading, essentially mapping conditions that may be invisible from the surface.

On a historic structure, ultrasonics can help determine whether a visually sound assembly contains internal deterioration. On new concrete or masonry construction, it can identify inconsistencies, voids, honeycombing, or other areas requiring further investigation before construction progresses.

Impact-Echo uses a similar concept but produces stress waves through a small mechanical impact. A sensor measures the waves reflected through the assembly, helping identify hidden voids, delamination, thickness variations, or separated masonry wythes. It is particularly useful on thicker masonry, concrete slabs, and structural elements where internal conditions cannot be visually confirmed.

Ground Penetrating Radar (GPR) answers a different question. Rather than primarily evaluating material integrity, it helps determine what is actually inside the assembly. A user moves a radar antenna across the surface while electromagnetic waves travel into the material and reflect from concealed objects or changes below the surface. These reflections can reveal reinforcing steel, anchors, wall ties, cavities, utilities, and changes in wall construction.

In restoration, that can mean understanding the construction of a century-old wall without dismantling it. During new construction, GPR can verify embedded components and be used before drilling, coring, or anchoring to avoid damaging something concealed within the structure.

Infrared thermography (IRT) is particularly useful when investigating moisture and building-envelope performance. Thermal cameras don't actually "see" water. They measure differences in surface temperature. Wet materials, air pockets, missing insulation, and other conditions can heat and cool differently from surrounding materials, producing recognizable thermal patterns.

In an existing building, investigators can scan walls or facades to narrow down areas affected by water intrusion, then verify those findings through moisture testing or selective openings. On new construction, infrared imaging can evaluate insulation continuity, air leakage, and other envelope deficiencies before completion.

The technology doesn't necessarily tell us why the condition exists. It tells us where to look.

Other Tools In The Toolbox
Not every assessment requires radar or sophisticated imaging.

A rebound hammer uses a controlled impact to provide a relative indication of surface hardness. Multiple readings can reveal inconsistencies across concrete or masonry and identify areas requiring closer examination.

Traditional impact hammer or sounding techniques remain valuable as well. By lightly striking stone, masonry, or concrete and listening for changes in response, an experienced investigator can identify areas that may be hollow, delaminated, or deteriorated beneath an otherwise sound-looking surface.

For structural evaluations of existing masonry, flatjack testing provides another level of information. A thin hydraulic jack is inserted into a carefully cut mortar joint. Controlled pressure and measurements of the masonry's response provide information about existing compressive stress and material behavior, which is particularly valuable when evaluating historic load-bearing masonry for rehabilitation, adaptive reuse, or structural modifications.

Seeing More Doesn't Replace Knowing What You're Seeing
Non-destructive testing has given the construction and restoration industries an extraordinary ability to understand buildings without immediately taking them apart. But none of these technologies provide every answer.

Ultrasonics can identify an abnormality without explaining its cause. Thermal imaging may reveal a moisture pattern without identifying where the water entered. Each technology provides an additional piece of information.

The real value comes from combining those findings with visual assessment, selective invasive investigation when necessary, and, most importantly, people who understand how masonry and building systems actually perform.

For restoration, that means preserving more original material, targeting repairs more accurately, and making better decisions before dismantling significant structures. For new construction, it provides another opportunity to identify deficiencies while they can still be corrected rather than discovering them years later as failures.

The technology may allow us to see beneath the surface. Experience is still what allows us to understand what we're looking at and decide what to do next.

Non-Destructive Testing in Masonry Investigation

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