Q:   What is Coatings Inspection?

A:    Coatings Inspection is a Quality Control process by which to ensure that Coating Specifications are adhered to, as well as a method to evaluate coating application and condition. Quality Control is properly carried out when Coatings Inspection procedures are performed before and during Coating Application in order to control the quality of the finished product. Coating Inspection done only after coating application amounts to "damage control".

Steps involved in Coatings Inspection include checking surface preparation to measure surface profile and ensure that the surface is free from contaminants such as soluble salts, amine blush, rust, and oil, followed by observation of Coating Application. The Coating Inspector will confirm that the correct coating is mixed properly, applied properly, and according to the specification for both the job and the coating used.

Determination of ambient and surface temperatures, relative humidity, and dewpoint are crucial steps in Coatings Inspection to prevent against coating failure.

After application, a Visual Inspection is made to assess for runs, sags, foreign inclusions, missed areas, or other obvious physical defects in the applied coating. It may be necessary to perform porosity detection (holiday testing) tests to identify pin holes, bubbles, or other discontinuities in the cured coating. Dry Film Thickness is measured using mechanical or electronic dry film thickness gauges to ensure adequate coverage according to specifications. Coating adhesion tests may also need to be performed to ensure that the finished project conforms to all applicable requirements.

In a Multiple-Layer Coating System, each layer of coating applied is inspected with the same rigour, to ensure a quality product that conforms to contractual specifications.


Q:   Can I use one coating thickness gauge to measure paint on both metal and non-metal surfaces?

A:    The answer is "no" - and "yes".

Technologies used to measure coating thickness on metal substrates do not work on non-metal materials, which means that probes that work for one substrate are unsuitable for the other.

Measurement of organic coatings on ferrous metal substrates is performed using either magnetic pull-off gauges, the most common of which are dial thickness gauges - commonly referred to as ‘banana gauges’ -and pencil-style gauges;  or electronic paint gauges that induce a magnetic current. Non-destructive measurement of paint thickness on non-ferrous metals is taken using electronic dry film thickness gauges employing eddy current principles.

Non-destructive measurement of dry film thickness on non-metal substrates requires the use of ultrasound technology. An ultrasonic transducer produces a signal that penetrates the coating and rebounds from the surface back to the transducer to allow the instrument to calculate coating thickness.

While it is not possible to measure paint thickness on metal and non-metal surfaces with the exact same probe, the introduction of DeFelsko’s new PosiTector Universal Gauge Body makes it possible to have one gauge body that will receive all PosiTector-model probes.  You can now convert your new-edition PosiTector from dry film thickness measurement on metallic substrates to dry film measurement on non-metal substrates simply by changing probes.

To learn more about PosiTector Coating Thickness Gauges, please click the link for PosiTector

Stone Tucker Instruments is DeFelsko's authorized distributor in Canada; call us for all your PosiTector and PosiTest coating inspection needs.


Q:    How often do I have to have my gauges calibrated?

A:    There is no hard-and-fast rule concerning re-certification intervals for coatings inspection and other quality assurance equipment, but there is a basis for best practice.

Many inspection instruments, such as coating thickness gauges, temperature / humidity / dewpoint equipment, and surface profile gauges, are purchased with a certificate of calibration traceable to national or international standards. The certificate of calibration confirms that the gauge is measuring within the tolerances specified by the manufacturer, according to testing equipment that has been shown to measure the same parameters according to accepted standards. Many industries these days, particularly in the energy sector (oil and gas pipeline and refineries, hydro generation, nuclear power generation, wind and solar power) require that quality assurance instruments be re-certified on a regular cycle, to ensure that they continue to measure within tolerances specified at original manufacture, and customers ask, "How often must we have our equipment calibrated?”

There is no over-arching rule concerning re-certification intervals, but some Quality Assurance programmes include a specification for certification intervals of either 6 months or one year. Increasingly, some energy companies are requiring calibration certificates be no older than 6 months. The equipment user should therefore refer to their contractual obligations and their own internal QA specifications to determine whether a required recertification interval has been specified.

In the absence of a required interval, a rule of thumb has traditionally been to re-certify most measuring instruments annually.

Of course, any time a gauge or probe has been damaged, exposed to serious negative influences (abrasive chemicals, sharp impact, liquid ingress), or appears to be malfunctioning or measuring out of specification, the user is advised to have the equipment verified by a qualified lab to avoid costly rework due to wrong values or adverse conditions when coatings are being applied. The cost of the calibration service is well worth the confirmation that the job is being done properly.

We recommended the original calibration certificate be scanned, and a digital copy kept on file with the owner, the original paper certificate be kept in a safe place at home office, and a scanned copy be kept with the equipment on-site, to ensure that there is copy available through the warranty period for every gauge that has been certified.

Stone Tucker Instruments is able to certify and repair all equipment types we sell. Our turn-around time is quick and our service standards excellent.



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