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Adhesion Testing BS EN ISO 2409: BS 3900-E6 BS EN 24624: ISO 4624

Scope and Field of Application

BS EN ISO 2409 and BS 3900-E6 are alternative names for the same method which is used to assess the resistance of a dry film of paint, varnish or related product to separation from a substrate when a right-angle lattice pattern is cut into the coating and penetrates through to the substrate.

BS EN 24624 and ISO 4624 and are alternative names for the same method which is used to assess coating adhesion by measuring the magnitude of a perpendicularly applied tensile force needed to detach or rupture the coating. It supersedes BS 3900: E10 which has been withdrawn.

There are no pass/fail criteria defined in the standards. This is a matter of agreement between the parties concerned.

The actual standards are copyright-protected documents and we are not able to provide you with copies. If required however, you can easily obtain copies from the British Standards Institution.

 

Summary of Methods

BS EN ISO 2409: BS 3900-E6

This standard defines how a lattice pattern (consisting of two sets of six cuts with the sets at a right angle to each other) should be cut through the film. This reduces the paint film within the lattice to 25 small squares of coating. The standard defines the spacing of the cuts and hence the size of the squares. This varies according to the thickness of the coating.

A piece of transparent adhesive tape of defined adhesion strength is then applied over the lattice and pulled off. The standard includes a six-point pictorial scale ranging from no coating removed to more than 65% of the squares wholly or partially removed.

The advantages of the method are:-

• it is a simple, low cost method.
• it can be used on test samples where there is only a limited area of flat surface available.
• it can be used on-site and in situations where it is not practicable to use a tensile test method.

The disadvantages of the method are:-

• it cannot be used on coatings that are more than 250 microns thick or those which have a textured surface.
• it is not a sufficiently severe test. Unless there are significant adhesion problems, most coating-substrate combinations will show little or no coating detachment.

BS EN 24624: ISO 4624

A suitable adhesive (two-pack epoxy, two-pack polyester or cyanoacrylate) is used to fix a test cylinder to the surface of the coating. Once the adhesive has cured, a blade is used to cut around the circumference of the cylinder and down to the substrate. A tensile testing tool is then fixed to the test cylinder and used to apply a gradually increasing force of up to 100 Kg per square centimetre. The force being applied at that point when the test cylinder detaches from the test piece is noted.

The advantages of the method are:-

• it gives you a quantified measure of adhesion
• it can be used on moderately rough and textured surfaces
• the fracture surfaces on the disc and substrate can be examined visually and by a number of analytical techniques in order to determine the mode of failure.
• it is applicable over a wide range of adhesion strengths.

The disadvantages of the method are:-

• you need at least 150 square centimetres of flat surface for each test.
• the substrate needs to be rigid and be capable of sustaining the applied force without fracturing.
• there is always the worry that the adhesive modifies the coating and affects the reading obtained.
• there are some coatings for which we are unable to find a good adhesive.
• we can use the technique on site but the time needed for the adhesive to cure makes it inconvenient especially in cold/wet environments

In our experience a reading of between 20 and 40 kg per square centimetre corresponds to acceptable adhesion. We class anything above 40 kg per square centimetre as good. We have not been able to find an adhesive which can sustain a force of greater than 200 kg per square centimetre so this is the effective upper limit of the test. The following conversion factors may be useful:-

To convert kg per square centimetre to pounds per square inch, multiply by 14.2

To convert kg per square centimetre to kilopascals or to kilonewtons per square metre, multiply by 98.

To convert megapascals to pounds per square inch, multiply by 145.

 

In practice if the coating system has very good adhesion you tend to get cohesive failure of the coating and, in some circumstances, of the substrate.

 

Sample Requirements

BS EN ISO 2409: BS 3900-E6

The test can be carried out using a single 150 x 100 mm coated test panel. We can normally carry out the test on coated objects provided the have at least three flat regions at least 40 x 40 mm. The coating must be non textured and less than 250 microns thick.

BS EN 24624: ISO 4624

We need at least three flat panels for each coating. They should be 150 x 100 x at least 3 mm. Steel or aluminium are the preferred substrates although we have used this test on coatings applied to rigid plastics. Unless the adhesion of the coating is poor, substrate like wood and masonry are liable to undergo cohesive failure first.

If you wish, we can prepare the test panels. The quantity of liquid paint we needs depends on the method of application. We will be pleased to advise you regarding our requirements.

 

Accreditation

PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS), to carry out these tests.

 

 

Please contact Peter Collins for further details.

 

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