Powdercoat | Testing
A variety of non destructive and destructive tests can (and should) be performed on powdercoated materials to ensure that the coating is carried out properly and meets these standards.
Gloss
Gloss is measured using a non-destructive test with a meter that shines a light at an angle onto the coating, and measures how much light is reflected. Gloss is measured in %, and the following is a guide to translating that to the rather imprecise terms commonly used.
| Description | Measured gloss % |
| High gloss | 80% + |
| Satin | 40-60% |
| Matt | 20-40% |
| Eggshell | 0-20% |
Adhesion
This is measured destructively with the “cross hatch test”. Scores are cut right through the coating to the substrate placed 2mm apart in both directions such that a series of squares of coating remain, unconnected to surrounding coating. These islands of coating are then attempted to be pulled off using a calibrated type of sticky tape. Any of the squares coming off indicates a failure. Being a destructive test this is performed on a test panel coated at the same time as the job.
Permeability
A test panel is placed in a domestic pressure cooker with about 2-3 cm water in it, and boiled for 2 hours at a pressure of 100 kPa. While some slight discolouration of the coating usually occurs, no loss of coating (delamination) is allowable, nor is any blistering, bubbling etc.
Cure test
Another destructive test where a sample panel is rubbed with a swab of cotton wool with a special solvent (Methyl Ethyl Ketone, or MEK) to see if any coating comes off. The rubbed panel is examined visually for loss of coating and the swab for removed coating.
Resistance to deformation
Three tests are performed on test panels. The first has a weigh falling a pre-determined distance (about 1m) with a shaped point impacting the material, and the impact point is examined for damage. The second places a cup shaped indentation to a precise depth and the impacted surface is examined for cracks in the coating. The third involves bending the sample panel through a fixed angle round a precise diameter of mandrel. In these tests no cracks, delamination or lack of adhesion should be apparent.
Colour
The colour of the coated panel is examined under set light conditions and compared against standards with normal corrected vision for colour match.
Resistance to scratching
Using calibrated pencils (H, HB etc) of known hardness, attempts to scratch the surface of the coating are observed.
Appearance
One of the most subjective tests, but made more repeatable by specifying the distance that the visual observation is made from. In effect this test says that if a defect is not visible to the naked eye from 1m, then it is not a problem.
Resistance to mortar
Bricklayers mortar is dropped onto a test panel and allowed to “set”. The mortar droplet should be able to be moved from the coating without using an implement, and without any detachment of the coating, or discolouration.
Resistance to salt spray
Test panels are placed in a salt spray cabinet under controlled conditions (either neutral or acidic) and after the prescribed period (often 500, 1000, 2000 hours) there should be no blistering or detachment of the coating.
