Make sure the finish is consistent with a mottling meter
In the world of coatings, mottling is a defect which causes splotches to appear in a finish – rather than being brilliant and clear, the coating dries with irregular stripes and spots of lightness variation throughout. This is especially an issue for effect finishes and metallic finishes. It is caused by film thickness variations or by the metal flakes of the coating becoming disoriented and grouping together abnormally. There are a range of causes behind mottling, but with a mottling meter you can determine the characteristics of the mottle and so unearth the culprit.
In this article we look at how the mottling meter works, and where to find mottling meters in the United Kingdom.
Mottling meter distinguishes between types of mottling
“Mottling” is a broad term used to describe a number of effects. The different causes of mottling also lead to slightly different visual phenomena. The most common types of mottling are caused by either faults in film thickness or distribution of metal or other flakes that create the effect.
- Flake disorientation – the resulting mottle is of varying sizes which results in a non-uniform appearance
- Film thickness – thinner and less covered areas of substrate allow glimpses through the metallic flakes, giving only partial or poor hiding at a variety of angles
Due to the fact that mottling is not one phenomenon but several, a lot of mottling assessment still happens visually. However, there are also instruments that are designed to detect mottling in a finish. For example spectrophotometers can be calibrated to detect mottling but they are time-consuming machines that check and cross-reference the appearance of a coating point by point. The specialised mottling meter works by measuring lightness variations over a large sample area from different angles – 15°, 45° and 60° measured from the specular reflection. The 15° angle reveals flake disorientation mottling, while the 45° and 60° angles reveal the thickness variation mottling. To make these measurements the meter is rolled across the surface for a distance of 10-100 cm.
Mottling meters in the UK market
The leader in the field of mottling meters is BYK-Gardner. The BYK Cloud-runner is a portable mottling meter that characterises mottling by its size and visibility. Flat and curved areas can be tested, and it is also possible to specify target values for batch approval and process control.
If you would like to know more about mottling meters, or need one for a business or project, we are here to help! Get in touch through the “Request a Quote” link beneath this article and our experts, in collaboration with our coating partners, will find the right instrument for your needs.