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December 2011

Coating Thickness Measurement on Concrete & Masonry Substrates

DeFelsko’s PosiTector 200 ultrasonic coating thickness gage is ideal for non-destructively measuring the dry film thickness of coatings on concrete and masonry substrates.

The Application

Masonry substrates include stone, brick, tile, cast concrete, pre-cast concrete, concrete block, asbestos-cement board, renderings and plasterboard. Masonry substrates are often porous with varying degrees of surface roughness. While useful in promoting adhesion, such porosity and roughness increases the difficulty in attaining repeatable thickness measurements.

Masonry coatings are used for a multitude of purposes including cosmetic appearance, durability, abrasion resistance, as well as protection from elements such as moisture, salt, chemical and ultra-violet light. Common coatings for concrete include latex paints, acrylics, lacquers, urethanes, epoxies, and polyester resins.

Primer layers are used as adhesion promoters, while overcoat layers serve as protection from surrounding elements. The ability of the PosiTector 200 to discern individual layers of coating is dependent upon the acoustic properties of adjacent layers, individual layer thickness, as well as the coating process itself.

The primary purpose for measuring coating thickness on concrete is to control coating costs while ensuring adequate protective coverage. Commercial contracts often require an independent inspection of the work upon completion.

A non destructive test method eliminates the need to repair the coating after inspection, saving time for both the inspector and the contractor.

Measurement Challenges

Traditionally a destructive test method is used to determine coating thickness on masonry substrates such as concrete. Coatings used on concrete range from hard to soft, smooth to textured, and cover a wide thickness range. The surface of concrete can be quite rough, which can create significant variations in thickness measurements.

DeFelsko's Solution

The ultrasonic PosiTector 200 C (standard or advanced) gage is ideal for measuring most coating on concrete applications. With a coating thickness measurement range of 50 to 3800 µm (2 to 150 mils), this gage is recommended for customers desiring a single non-destructive measurement solution for most applications. The PosiTector 200 C requires little or no calibration adjustment for most applications. Figure 1 provides a cross-sectional view of a representative 125 to 375 µm (5 to 15 mil) coating on large aggregate concrete that is ideal for the PosiTector 200 C.


Figure 1: Coating on rough, large aggregate concrete

The ultrasonic PosiTector 200 B gage is ideal for measuring coating thickness from 13 to 1000 µm (.5 to 40 mils). While not specifically designed for measuring on concrete, after a simple calibration adjustment the 'B' probe may demonstrate improved repeatability when measuring hard, thin coatings over smooth surfaces. Figure 2 represents an application where the PosiTector 200 B may be preferred.


Figure 2: Thin coating on smooth, cement surface

If the concrete surface is smooth but uneven, or rough and porous, one would expect the measurement values to vary accordingly. When examined under magnification, locations where the coating has flowed into pores or crevices may appear as outliers when measurements are taken. For example in Figure 3, the bump in the substrate at "A" results in a significantly different thickness than nearby point "B". It is up to the user to compare results to the specification or expected thickness when analyzing results. Some results may need to be omitted when making calculations.


Figure 3: Thick soft coating on concrete

For an application such as Figure 4, that has both a rough substrate and a rough coating surface, it may be necessary to take several readings within individual small areas, calculate average readings, and then compare these values. These averages can then be compared against the specification. Destructive testing on the sample shown in Figure 4 identified a 1 to 3 mm (40 to 115 mil) variation within a Ľ” diameter area.


Figure 4: Coating on rough lightweight concrete


How to Measure

Ultrasonic testing measurement works by sending an ultrasonic vibration into a coating using a probe (i.e. a transducer) with the assistance of a couplant applied to the surface. A 4 oz bottle of a common water-based glycol gel is included with every instrument. Alternatively, a drop of water can serve as couplant on smooth, horizontal surfaces.

Figure 5: Taking a measurement

After the drop of couplant has been applied to the surface of the coated part, the probe is placed flat on the surface. Pressing down initiates a measurement (see Fig. 5). Lifting the probe when a double beep is heard holds the last measurement on the LCD. A second reading may be taken at the same spot by continuing to hold the probe down on the surface. When finished, wipe the probe and the surface clean with a tissue or soft cloth.


Graphics Mode (PosiTector 200 Advanced Models Only)

The right hand side of the PosiTector 200's screen can be used to display a graphical representation of the ultrasonic pulse as it passes through the coating system. This powerful tool enables the user to better understand what the gage "sees" below the surface of the coating.

Figures 6 & 7:
Left: PosiTector 200 C3 with Graphics Mode ON
Right: PosiTector 200 C3 with Memory Mode ON


The PosiTector 200

DeFelsko’s PosiTector 200 coating thickness gage is ideal for coating thickness measurement over a variety of non-metal substrates.

Two models are ideal for masonry coatings:

1. The PosiTector 200 C1 is the economical and most common solution for measuring the TOTAL coating system thickness.

2. The PosiTector 200 C3 is capable of measuring both TOTAL coating thickness AND up to 3 individual layer thicknesses in a multi-layer system. It also features a graphic readout for detailed analysis of the coating system.

Each PosiTector 200 comes complete with probe, protective rubber holster with belt clip, couplant, 3 AAA batteries, instructions, nylon carrying case with shoulder strap, Certificate of Calibration traceable to NIST, two (2) year warranty.

Size: 146 x 64 x 31 mm (5.75" x 2.5" x 1.2")
Weight: 165 G (5.8 oz.) without batteries

Conforms to ASTM D6132 and ISO 2808


Free Consultation


For current pricing or to order these instruments, please contact us by e-mail at techsale@defelsko.com, by telephone at +1(315) 393-4450 or by fax at +1(315) 393-8471. If you require additional technical information or have questions relating to your particular application, we encourage you to take advantage of our years of experience in recommending the best gage for your needs.

 

 


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