How to check paint adhesion? Let's discover the Grid or Adhesion Test

The grid test is a quick and simple system for evaluating the adhesion of paint systems, and is very useful in order to avoid starting to paint a surface that has poor adhesion.

Carrying out tests, sampling and checks before undertaking any work related to the painting of metal and plastic is essential to understand the potential outcome, so as to be able to propose the best possible solution and always knowing precisely what to expect from a specific type of treatment.

Let us always remember that painting is not always and only an aesthetic parameter, it is often also an important factor against corrosion, oxidation and the action of other external agents that could limit the life cycle of a product, such as water and sun.

In the case in question, it is important to understand whether the paint is adhering perfectly to the surface or whether problems could arise, even if at a first superficial evaluation everything seems to have been done well.

A very effective test to verify the compactness and adhesion of the existing paint consists in making various incisions spaced a couple of millimeters apart on the affected surface. These incisions must be deep enough to directly touch the surface beneath the paint layer.

Using a crosshatch tester, also called crosshatch tester or adhesion tester, it is necessary to form a lattice through a series of horizontal and vertical incisions, forming squares measuring 1x1mm, 2x2mm or 3x3mm.

After having made the incisions, it will be sufficient to place some Permacel or 3M type adhesive tape on the affected part (specifically designed for squaring tests). If, when removing the tape, part of the paint remains attached to the adhesive, it means that the adhesion is poor and, therefore, applying a further coat of paint over it could certainly cause it to detach.

This test, called the grid or adhesion test, is a quick and simple system for evaluating the adhesion of paint systems; it is very useful in order to avoid starting to paint a surface that has poor adhesion, and will avoid having to redo a job because it was not carefully evaluated in the initial phase.

If the grid that has been created is completely flat, with the edges of the lines perfectly clean, it will mean that the painting is suitable and it will be possible, where required, to apply a further layer of coating over the current one (this is the case with ISO value 0).

If, in the opposite case, the edges of the lines are not clear, but there are detachments of paint at the corners or along the various lines, it means that the treatment is not perfectly adhering to the surface.

In this case it will be necessary to evaluate the level of severity of the situation, with an ISO value that can range from 1 to 5, where 1 represents small detachments from the intersections of the lines (equal to no more than 5% of the tested area) and 5 a level of detachment greater than 65% of the area, a situation absolutely not compatible with a need for painting and which will require a total scraping of the current surface before it can be further worked.

The reference standard that regulates this test is ISO 2409:2020, where the test method is clearly defined, with instructions illustrating in detail how to carry out the test appropriately. Our internal laboratory is perfectly capable of carrying out the test, with expert technicians who can carry it out in a short time and reveal the outcome in complete safety.

The grid test is one of the simplest and most practical methods to understand whether the adhesion of a coating is optimal or not, both on metal and plastic supports, and for this reason its use is strongly recommended.

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