Assessment of Cracking

BS 3900-H4 : ISO 4628/4

 Cracking

Scope and Field of Application

BS 3900-H4 and ISO 4628/4 are alternative names for the same method. It is one of a series of methods of designating the quantity and size of common types defects in paint coatings. Other methods in this series deal with the assessment of blistering, chalking, flaking and rusting.

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

The actual standard is a copyright-protected document 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 Method

It is important to emphasise that the standard describes a method of assessing cracking. It is not a method for testing the resistance of a coating to cracking. If you need to test for resistance to cracking before weathering, then please refer to our flexibility test page. If you wish to assess the effect of weathering on flexibility, you should visit our durability test pages. We will of course be pleased to advise on the most appropriate test for your samples.

The standard is basically a collection of drawings of cracked surfaces showing both linear and random cracking that vary in density. The sample is compared with these drawings and given the rating of the drawing that bears the closest resemblance.

The standard also includes a table which enables you to rate the size of the cracks on a six-point scale ranging from no cracks visible under x 10 magnification to ones that are more than 1 mm wide.

Sample Requirements

This assessment is normally carried out using test panels that have been subject to some form of durability testing and the panel size and number will have been selected for that purpose. Basically all we need is a representative test piece with an area for assessment of at least 100 x 100 mm.

Accreditation

PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS) to carry out this test.

 

Please contact Peter Collins for further details.

 

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