The Constructor

Magnetic Rebar Locator – Covermeter Test Applications and Precautions

Magnetic Rebar Locator (covermeter) test

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Covermeter test is a nondestructive test which is used to specify the location of reinforcement bars in concrete and determine the exact concrete cover needed. The magnetic rebar locator test plays a significant role in construction works because the information about the location of steel bars, concrete cover, and bar sizes is essential, directly or indirectly, in many field applications.  

For instance, knowing the diameter of a bar and its location is needed to understand the spacing of bars and their placement in existing structures where drawing may not be available.

Added to that, in cases where the core extracts of a concrete specimen are to be taken, the identification of the locations of rebars becomes essential to avoid the cutting of the same. It is important to note that the cover meter test is not applicable for certain types of bars such as Glass fiber and post tension or pretension strand.  

Field Applications of Covermeter Test

  1. Making drawings for old buildings for maintenance purposes
  2. On-site testing of reinforced structures.
  3. Drilling and core cutting
  4. Conformity check of new buildings
  5. Investigations on unknown structures
  6. Corrosion analysis
Fig. 1: Avoiding Rebars during Core Sampling

How does the Covermeter Test Device Work?

A covermeter is a device that gives information about concrete covers and steel reinforcement in concrete using magnetic fields. Magnetic instruments for locating reinforcement steel (present within the concrete) work on the principle that the steel affects the alternating magnetic field.

When a hand-held search unit is moved along the concrete surface, a beep indicates that the unit is located directly above a reinforcing bar. These meters can also be used to estimate the depth of a bar if its size is known, or estimate the size of the bars if the depth of cover is known.

However, detailed calibration is needed to get satisfactory results. The bars may be located within 175 mm of the concrete mass but the method is not effective in heavily reinforced sections, sections with two or more adjacent bars or nearly adjacent layers of reinforcement.

Inaccurate results may occur when the depth of concrete cover is equal to or close to the spacing of the reinforcing bars. During this test, steel or other metals must not be present close to the area under examination. Some results from tests must be calibrated by chipping of concrete to confirm concrete cover and bar size.

A number of pachometers are available that range in capability from merely indicating the presence of steel to those that may be calibrated to allow the experienced user a closer determination of depth and the size of reinforcing steel.

Fig. 2: Covermeter Device


  1. When the element is reinforced with two layers of steel bars, it is recommended to start the location with the first layer. The location of the second layer cannot be determined easily provided the layers are too close to each other.
  2. It is recommended to select a place on the structure where there is sufficient spacing between the rebars in order to determine the diameter of bars precisely.
  3. It should be noted that the accuracy of covermeter test devices reduces as the concrete cover increases.
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