Coatings need inspections and maintenance! This is sometimes forgotten, but the longevity of a covering is closely linked to an annual check; also possibly updating small anomalies at that time will extend its lifespan. On the other hand, “to measure is to know” also applies here. It is better to be prepared for the replacement of a covering and reports give a clear picture of how the covering is evolving and within how much time a replacement may be necessary. GBT strongly encourages checks, which means that we can also give longer guarantees. We are able to act to limit damage. Minor mechanical damage can have disastrous consequences: what costs € 500.00 with a quick determination, can amount to damage of more than € 100,000.00 in 12 months!

What do we check?​


One of the simplest things is the visual inspection! Simple but very important; Of course an experienced eye is important for this inspection, the upholstery is only as protective as its weakest point. During this inspection, the general condition and quality are examined. We look for known deficiencies such as blistering (diffusion), encapsulation, cracks or e.g. mechanical damage. Particular attention is paid to hard-to-reach zones, sealing surfaces, grooves, edges, etc. The top layer itself is examined, discoloration, roughness, etc.


All accessible areas of the cladding are examined by means of knock on the door, cavities are carefully opened so that the underlying damage can be accurately described, whereby the following matters are very important: is the cavity filled with liquid? How far does the hollow space go (substrate or in the cladding), what is the condition of the subsurface, has corrosion already occurred? These spaces usually indicate a diffusion process that has started.

Layer thickness measurement

The purpose of this check is, by means of to take random measurements of certain places of the revetment and thus to determine a statistical certainty of the real thickness of the entire revetment and to determine any deviations from the theoretical minimum thickness. (or compare with previous inspections)
During these measurements, it is determined whether the coating was applied evenly and at the layer thickness or whether there is a decrease in material due to wear and tear, for example.

Pore breakdown / Insulation measurement

When measuring the porosity and the insulation by means of spark testing, the insulation quality of the cladding is checked; at the same time, mechanical damage and further defects in the coating are detected. If the coating is undamaged, an electrical breakdown occurs when the breakdown voltage is exceeded. If damaged, however, a breakdown is already obtained at low voltage. Uncontrolled build-up of sparks forms stray currents on a large surface, targeted spark build-up (bright spark), on the other hand, is a clear indication of porosity/damage down to the steel substrate.
The voltage level is determined by the manufacturer of the coating, is based on the expected insulation value, age and is calculated on the basis of the layer thickness that was measured on site.

Hardness measurement

The hardness of coatings is measured according to ASTM with the Barber/Coleman method or according to DIN 14879. The depth of penetration or the resistance of the measuring device in/of the coating counts as the degree of hardness and is shown in units of scale e.g. Barcol-Hardness of Shore. The degree of curing achieved depends, among other things, on the temperature during processing.
The Barcol hardness is an indication of the correct composition of resin, hardener and accelerator. The higher the hardness of a coating, the better the mixing of the resin (polymerization) achieved and therefore also the chemical resistance. The hardness not only gives an indication of the previous application, but can also give an indication of, for example, a chemical attack. Shore measurements are done e.g. on ebonite and soft rubber.

Adhesion measurement

This test is an ideal way to test the internal condition of the liner as well as its manufacturing quality. During the adhesion measurement, a test piece of 20 mm in diameter is manually glued to the place where the coating was applied. This test piece is pulled off the substrate with a calibrated adhesion meter. You can immediately read the degree of adhesion of the coating on the measuring instrument in N/mm².

Adhesion values are indicated by the manufacturer, these are usually degressive, i.e. the starting value with new coating is higher than the minimum value after service. Not only the determined degree of adhesion is essential, but also the break line of the adhesion test. The fracture line shows the extent to which the coating still adheres sufficiently, i.e. whether the coating is still fully bonded to the steel substrate.
All above-mentioned reported parameters lead to a global picture of the condition of the coating.


The results of the aforementioned tests are bundled, lead to decision making:

  • What is the expected further life span?
  • Is action required and when?
  • Is the coating the right one for this application?

GBT recommends that an inspection is carried out at every opportunity, at least annually. If the device frequently goes out of service, it is advisable to have your own maintenance service carry out the visual inspection. Early intervention can prevent serious damage and unnecessary costs.

GBT has a very extensive team of trained inspectors, all equipped with the necessary modern inspection equipment.