What is the cross-cut test?

The cross-cut test (also called the cross-hatch test or grid test) is a quick, practical test to assess how well a paint film, varnish or coating adheres to its substrate. With a knife you cut a grid of small squares through the film down to the substrate, press a piece of tape onto it, pull it off in one go and look at how many squares come away. The method is laid down in the standard EN ISO 2409 (in the Netherlands NEN-EN-ISO 2409); in the American world, ASTM D3359 is the comparable standard.

How the test works

1. Make six parallel cuts through the paint film down to the substrate, then six cuts at right angles to them. This produces a grid of 25 squares.
2. Choose the cut spacing according to the film thickness. As a rule of thumb from the standard: 1 mm for thin films up to about 60 micrometres, 2 mm for films up to about 120 micrometres and 3 mm for thicker films up to about 250 micrometres.
3. Brush away loose particles with a soft brush.
4. Apply tape firmly over the grid, rub it down and, after a short time, pull it off in one movement at a sharp angle.
5. Assess the result using the classification 0 to 5. Class 0: all cut edges smooth, nothing detached. Class 5: more than 65 per cent of the area has come away.

For most applications, class 0 or 1 is regarded as good.

Applications

• Checking before painting: if you are unsure about an old paint film (glossy, flaking, unknown paint system), a cross-cut test shows whether you can paint over it or need to strip or sand it first.
• Handover and disputes: painters and coating companies use the test to demonstrate that a system adheres properly.
• New substrates: on galvanised steel, uPVC window frames and tiles, adhesion is often the problem. After applying the primer, always test a trial patch first.

Common mistakes

• Not cutting down to the substrate. Then you are only testing the top layer.
• Testing too early. The paint must be fully cured; follow the manufacturer’s drying time.
• Testing in a visible spot. The test damages the film. Choose an inconspicuous place.

Related terms

• Adhesion
• Enamel paint
• Types of wall paint
• Corrosion

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