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Concrete, Brick & Other masonry non-destructive test methods & equipment:

This article describes and provides research on a wide range of non-destructive inspection & test methods, tools, procedures & standards used to examine concrete structures as well as masonry block, brick and other structures for hidden damage such as cracks, voids, omission of steel reinforcement, re-bar corrosion, and similar concerns.

This article series explains how to recognize, diagnose, & repair concrete & other masonry materials used for foundations, walls, floors, roofs, and other structures. These methods can evaluate the masonry or solid concrete for signs of failures such as cracks, spalling, movement, bulging, leaks, damage due to impact, settlement, frost or water damage, corroded re-bar, corroded steel beams, vibration, and other problems.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Non-Destructive Inspection & Test Methods for Concrete, Block & Other Structures

Structural brick wall with rain screen opening between wythes © D Friedman at

Methods of Detection of Hidden Cracks or Other Structural Damage in Concrete & Masonry Walls & Foundations are described here.

Question: Is it possible to detect cracks in brick walls or concrete walls and slabs that are hidden from view by plaster?

2017/05/29 Parth Bathia said:

Is it possible to detect cracks in brick walls or concrete walls and slabs that are hidden from view by plaster?

Like there is no through and through air pockets.

If there is a way. I want to know how is it possible to detect the same.

I get the use of thermal imaging but that is only possible for detecting temperatures on surface.

I want something that might be able to detect cracks that is hidden about 6 - 8 inches inside the walls without breaking or damaging the wall.

This question was posted originally at BRICK FOUNDATIONS & WALLS


What an interesting question; thank you. I have some obvious and some speculative answers:

1. Obvious cracks will often show up through plaster if there is ongoing movement in the masonry wall that has been plastered-over, either as plaster cracks or sometimes as a plaster bulge.

2. With thermal imaging there is a small chance you'd see a wall crack IF the crack were leaking water AND you happen to scan the wall when the leak is enough in quantity and lower temperature to show up as a temperature variation - but I'd consider such "detection" speculative.

3. There are non-destructive testing methods (such as the Echo Impact method) that can find cracks or voids in masonry structures, though in my opinion those are going to work best on placed (poured) concrete that would not be expected to have many voids.

A structural brick wall will usually have an interior wall cavity and may have many other smaller voids that can be confusing when using an echo-impact masonry void detector.

Types of Non-Destructive Methods for Concrete Damage Detection

Parking level collapse at Northridge Meados, Los Angeles Earthquake (C) Daniel Friedman at InspectApedia.comThe tools and methods listed below are used by experts to screen or scan concrete structures for various defects such as delamination, voids, or large cracks. I'm doubtful that many of these work very well on a brick wall for reasons I cited above.

Photo: Partial collapse of the rear or West parking lot at Northridge Meadows after the Los Angeles earthquake. Even as a layman inspecting this collapse it appeared to me that even by casual inspection - after the catastrophe - one could see that the steel reinforcement had been interrupted when and just where the collapsed section of raised parking lot had broken and collapsed during this earthquake.

More about the Northridge Earthquake is at EARTHQUAKE DAMAGE PHOTOS CA 1994

Article Contents

Drossbach & Similar Grouted Joint & Rebar Assessment

Definition: Drossbach ducting is a metal tube manufactured from galvanised steel to create a spiral round duct that may be used along with rebar and grout to connect pre-cast concrete building components such as wall panels and floors.

Definition: A Drossbach-type joint combines the ducting with re-bar and grout to join these building components. Drossbach ducting, rebar and grout jproduces post-tensioned tendons used to secure the joint between the precast wall and floor or for similar connections.

The Drossbach joint may use 0.3mm galvanised steel strips with an internal diameter from 33 to 107mm- Adapted & expanded from Contech cited below.

[Illustrations needed, CONTACT us if you can provide images.]

In New Zealand experts are finding increasing examples where grouted rebar connections typically between concrete floor and precast wall panels have not been addressed, compromising seismic performance and leading to horizontal cracking between floor and walls on external faces - see first link, below, courtesy of Paul Probett, Incodo, New Zealand, for suggesting this topic.

Overstrength factors for reinforced concrete structures are defined in the New. Zealand Concrete Structures Standard, NZS 3101:2006

Mr. Probett, director of Incodo, Forensic Building Pathology, can be contacted at Incodo Ltd., Post Box 8202, Cherrywood, Tauranga, 3110, Courier 4/511 Cameron Rd, Tauranga, New Zealand, tel: +64 7 578 7499 M +64 27 28 000 36, Email: Website: Skype: paulprobett

More research on detection of missing rebar, Drossbach grouted joint assessment, voids in concrete, & re-bar assessment

CONTACT us if you have suggestions for this topic.

Concrete and re-bar joint assessment tools include GPR (Ground Penetrating Radar), electrical resistance and other electrical tests, and other methods discussed by the authors cited below.

Thermography for Detecting Damaged Masonry Structures

Thermal image example, Paul Probett, Incodo 2008

Image courtesy Paul Probett, Incodo, cited at the Thermal Imaging Thermography article linked-to below.

Infrared Scanners (IR) or Thermography (IT) can detect temperature variations across a masonry surface.

Watch out: Using either an IR thermometer that measures temperature variation, or currently more popular, diagnostic, and more expensive, thermal imaging can show up the presence of moisture IF the moisture or leak is current.

IR or IT will not reliably show up leaks whose moisture has dried since the leak occurred, though some other moisture meters that rely on resistance measurement might detect mineral salt variations left behind by prior leaks (efflorescence).



Delmhorst pin type moisture meter with long probes © Daniel Friedman at

Moisture Meters for Masonry Structure Damage Detection

Moisture meters, both pin-type and electronic, can detect variations in the moisture level across all types of masonry surfaces.

The depth of sensing of pin type moisture meters (shown above) is limited to the depth of penetrations of pins of the sensor into the material, while an electronic moisture meter (shown below) can penetrate inches into the material, depending on its density and electrical properties.

Tramex moisture encounter in field use © Daniel Friedman at

As with our IR and IT scanning comments in this article, a moisture meter won't reliably detect prior leaks that happen to be dry at the time of inspection and testing.

See MOISTURE METER STUDY for a description of the effectiveness of different types of moisture meters used in buildings.

Ultrasound or Ultrasonic Detectors for Detecting Masonry or Concrete Structure Defects

Ultrasonic testing devices use a probe and sensor that can measure the thickness of steel reinforcement or steel beams that are nearly-buried in a masonry structure, as long as one side of the steel member can be accessed. This approach might permit detection of rust damage or loss of steel material in the hidden interior of the structural wall, roof, or slab.

Vibration Monitors for Concrere Structure Assessment

Vibration monitoring can assess the amount of building movement caused by traffic, an earthquake, or nearby construction work or blasting. Vibration monitoring is particularly apt to monitor nearby buildings for the impact of an ongoing construction project.

Photograph: using a borescope to examine a building wall cavity

Borescopes for Investigating Structural Damage to Buildings

A borescope won't be much help in an external screen of a masonry structure for hidden damage but it might allow a view of exposed surfaces that are blocked by obstructions such as a radiator or HVAC equipment. A simple inspection mirror and a good light may also suffice. Borescopes can give a limited view of the inspection of a wall cavity. So you might inspect the cavity side of a brick veneer wall by probing the wall cavity from the building interior.

See HIDDEN MOLD in CEILINGS / WALLS for examples of better use of a borescope.

Pachometer Tests on Masonry Structures

A pachometer is a non-destructive magnetic sensor that can find buried steel in masonry structures. A pachometer can be used thus to find re-bar, reinforcing steel mesh, and hidden steel beams.

Keep in mind that pipes, expanded metal lath, metal conduit will also be detected by this tool. Technical use of a pachometer in evaluating a concrete structure would be the confirmation of re-bar spacing and sizes as well as depth of the re-bar in a concrete ceiling, roof, wall, foundation, or slab. We might aso use a pachometer to check the depth of metal radiant heat piping in an older radiant heat floor.

Flat-Jack Tester & Flat Jack Testing Methods for Masonry Wall Damage Assessment

Flatjack testing can detect deformed or stressed unreinforced masonry walls (concrete block, brick) and may detect deformation in concrete walls & foundations. Flatjack testing is also described (Carpinteri 2004) as acoustic emission (AE) technique, a non-destructive instrumental investigation method ... to measure and check the evolution of damage in concrete and masonry structures.

Ground Penetrating Radar for Building Reinforcement Assessment

Crack monitor (C) Carson Dunlop Associates

Ground penetrating radar (GPR) is widely used in broad-scope sitework to locate buried metal items such as a buried oil tank.

GPR uses an electromagnetic pulse that is reflected back to the instrument at varying signal levels based on what the pulse encounters in the pulsed area. Synonyms for ground penetrating radar or GPR include EMR (Electromagnetic Reflection), SIR (Subsurface Interface Radar), georadar, subsurface penetrating radar, and soil radar. (Blindow 2007).

GPR is also used in a more-technical application to find buried steel beams or reinforcement in a concrete structure. GPR can report on the location and thickness of steel or other metallic components hidden from view in solid structures, including re-bar, steel mesh, beams, as well as conduit and metal water pipes, even metallic ducctwork.

Avongard crack monitor (C) Avongard Co.

Strain Gauge Testing Equipment for Monitoring Movement or Deformation in Masonry Structures

Strain gauge monitoring equipment or devices are affixed in place across concrete, masonry block, brick or other surfaces where cracks are to be monitored for movement, deformation, or change.

Once the Crack Monitor is in position across a crack, the cross hairs shift vertically or horizontally on the grid if movement occurs,so that anyone can easily see and track crack movement." (Photo at left of a crack monitor in place is courtesy of Carson Dunlop Associates.)

See CRACK MONITORING METHODS - Methods for Monitoring Foundations for Evidence of Ongoing or Episodic Movement.

Impact Echo Testing for Concrete Structure Defects

Impact-echo testing, one of the most widely-used concrete testing method for concrete and masonry, combines an impact device and sensor with (typically) a computer and special software to analyze sound waves or vibrations in solid concrete structural walls, floors, ceilings.

Impact echo testing can locate areas of damage to the concrete structure that are not readily visible, such as cracks in a concrete wall that are covered by plaster. Echo tests can report on the location, size, pattern, and thus severity of cracks in the structure.

Rebound Hammer Method for Testing Solid Masonry: concrete

A rebound hammer is used to evaluate the quality and uniformity of "cured" or hardened concrete walls, floors, foundations. ASTM C805 describes the use of this test to assess the uniformity of concrete "in place" and to find "regions of poor quality or deteriorated concrete".

The accuracy of this test method is affected by a number of site factors including the smoothness of the concrete surface, the age and moisture content of the concrete, extent of surface carbonation, the use of aggregate and its properties, the presence of air voids, the nearby presence of reinforcing steel, the concrete temperature, and the care with which the rebound hammer was calibrated.

CEMTEX offers this clear description of the rebound hammer:

The [rebound hammer] consists of a plunger rod and an internal spring loaded steel hammer and a latching mechanism.

When the extended plunger rod is pushed against a hard surface, the spring connecting the hammer is stretched and when pushed to an internal limit, the latch is released causing the energy stored in the stretched spring to propel the hammer against the plunger tip. The hammer strikes the shoulder of the plunger rod and rebounds a certain distance.

There is a slide indicator on the outside of the unit that records the distance traveled during the rebound. This indication is known as the rebound number. By pressing the button on the side of the unit, the plunger is then locked in the retracted position and the rebound number (R-number) can be read from the graduated scale.

A higher R-number indicates a greater hardness of the concrete surface. - CEMEX Technical Bulletin No. 2 (2013)

Half-Cell Tests for Metal Corrosion in Masonry Structure Reinforcements

Half-cell testing is an electronic test method that guesses at the level of active corrosion of steel reinforcement (re-bar or steel mesh) in reinforced concrete structures. In most-general terms, a half-cell test for metal corrosion is based on the reaction of anodes and cathodes.

A voltmeter has its positive lead connected to an exposed end of steel reinforcement in a concrete structure such as an end of a rebar. The negative lead of the voltmeter is connected to a reference electrode that is placed on to the surface of the concrete. (Gu 1998)

Factors influencing the accuracy of half-cell tests on concrete to screen for corrosion of its rebar include the oxygen concentration at the interface of the re-bar and the concrete, the amount of concrete carbonation (reaction between atmospheric CO2 and CaOH in the concrete that reduces the pH of the steel-concrete interface, chloride ion concentration, the use of corrosion inhibitors at the time of construction, the use of expoxy-coated or galvanized re-bar, the density of the concrete cover, the use ofhigh-resistance concrete, the presence of organic coatings or sealants on the concrete surface, the presence of a concrete patch or other repair, and the presence of cathodic protection systems attached to the re-bar along with the problem of stray electrical currents.

Although it was blamed on excessive piling up of snow, the 2007 collapse of a section of the Poughkeepsie Galleria's parking garage might have been predicted had a prior survey been made using Half-Cell testing and a Pachometer to assess the presence of steel reinforcement as well as its condition.


Continue reading at CONCRETE FOUNDATION, WALL, SLAB DEFECTS - home, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see BRICK FOUNDATIONS & WALLS damage assessment,

Or see FOUNDATION CRACK DICTIONARY detailed process of evaluating foundation cracks and signs of foundation damage by examining the crack size, shape, pattern, and location.

Or see FOUNDATION BULGE or LEAN MEASUREMENTS explains a simple method for determining how much bulge or lean is present in a foundation or wall,

Or see FOUNDATION MOVEMENT ACTIVE vs. STATIC helps determine if the foundation movement is ongoing

Or see FOUNDATION DAMAGE SEVERITY discusses how we decide the severity of foundation damage and the urgency of further action

Or see these

Concrete Crack Diagnosis & Repair Articles

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