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Determination of Through Drying Time and RecoatabilityBS 3900-C3 : ISO 9117: BS EN 29117 |
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Scope and Field of Application
BS 3900-C3 , ISO 9117 and BS EN 29117 are alternative names for the same method which is intended for the determination of the through drying characteristics of a paint or varnish film which dries by reaction with air or by a chemical reaction of its components.
This method gives a measure of the time that elapses between the application of a coating and that moment when not only the surface but the entire thickness of the film is dry. We normally supplement this method with an in-house determination of recoatability.
A separate test is required to determine how long it takes for the surface alone to dry completely. Please refer to the surface drying test page for details of the method.
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
The coating is applied to a number of test panels which are then left to dry under defined temperature and humidity conditions.
At suitable intervals, one of the panels is selected and tested using a machine which presses a gauze fabric covered plunger against the film and then rotates it through 90 degrees. If the film is not through-dry, this process will cause visible marring of the surface.
If the surface of the coating is damaged or marked, the panels are left to dry for a further period and then the whole process is repeated using a fresh panel.
The time at which the painted surface is just dry enough to remain unmarked during the test is taken as the through-dry time.
This method can also be used as a pass/fail test for through-dry after a defined time period.
We normally carry out an in-house determination of recoatablility as soon as the through-dry stage is reached. This involves application of the coating, by brush, to the newly through-dried film. Any drag on the brush or rivelling of the film when dry is noted.
Our experience of this test is that, at 20°C and 50% relative humidity, solvent borne decorative gloss paints generally through-dry within eight hours while decorative matt emulsion paints take about 45 minutes.
Sample Requirements
We require 250 ml of sample together with information regarding the film thickness at which the coating should be applied.
Accreditation
PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS) to carry out the drying time test. We are not accredited for recoatability testing.
Please contact Peter Collins for further details.
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