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Scrub Resistance and Cleanability BS EN ISO 11998 DIN 53778: Part 2 ASTM D 2486

Scope and Field of Application

BS EN ISO 11998 is a method for measuring the ability of coatings to withstand wear caused by repeated cleaning operations and to resist permanent blemishing by stains.

DIN 53778: Part 2 differs experimentally from BS EN ISO 11998 but has a similar scope and application.

ASTM D 2486 is a method for determining the resistance of wall paints to erosion caused by scrubbing. Unlike the other two tests it does not include any measurement of cleanability.

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 either the British Standards Institution, the Deutsches Institut für Normung or the American Society for Testing and Materials.

 

Summary of Methods

All three methods involve the use of a scrub testing machine. This consists basically of a motor driven reciprocating arm which moves a brush or pad across the surface of the paint film under test. The methods differ in the stroke length and frequency and the nature of the brush/pad and cleaning liquid:-

Test	Stroke Length (mm)	Stroke Frequency (cycles/minute)	Number of Cycles	Nature of Brush/Pad	Nature of Scrubbing Agent
BS EN ISO 11998	300	37	200	Plastic pad with embedded abrasive	0.25% aqueous solution of dodecylbenzenesulphonate
DIN 53778: Part 2	430	37	Continue until defined failure point reached	Pig bristle brush	0.25% aqueous solution of dodecylbenzenesulphonate
ASTM D 2486	Not defined	37	Continue until defined failure point reached	Nylon bristle brush	Abrasive medium based on aqueous dispersion of silica

 

The tests are carried out as follows:-

BS EN ISO 11998

The test coating is applied to a test panel at such a thickness that the dry film can withstand 200 scrub cycles without wearing through. After drying and ageing for an agreed period, the coated panel is weighed and then subjected to 200 wet-scrub cycles. After washing and drying, it is then re-weighed in order to determine the mass loss. The mean loss in film thickness is then calculated ( this requires prior determination of the non-volatile density of the coating. This is done by weighing a measured area of the dry coating. The standard defines a method for carrying out this determination).

The mean loss in film thickness is taken as a measure of the scrub resistance of the test coating.

The test coating is assessed for cleanability using similar test panels to those used for scrub testing. The panels are soiled (the soiling materials and the method of application is agreed between interested parties) and then subjected to the scrub test as detailed above. The panels are then assessed visually in order to determine the extent to which the soiling material has been removed.

DIN 53778: Part 2

This test is designed to measure scrub resistance and cleanability at the same time. The test coating is applied to a test panel so as to yield a dry film thickness of 100 microns. After ageing for 28 days, the coating is soiled using pencil, charcoal and crayon marks. This soiled sample is scrub tested and a note is made of the number of cycles needed to remove the soiling. The test is then continued until the coating is worn through (the standard includes a pictorial guide which helps to define "worn through").

The number of cycles need to remove the soiling gives a measure of the cleanability while the number of cycles needed to wear through the coating is taken as a measure of its scrub resistance.

ASTM D 2486

Unlike the other two methods, this test only measures scrub resistance. The test coating is applied to a test panel using an applicator with a gap of 180 microns. After ageing for 7 days, the coated panel is scrub tested until the coating is worn through. The method also allows for the use of a reference coating which is tested at the same time. In this case the test continues until both the test and the reference coatings are worn through

In the absence of a reference paint, the number of cycles needed to wear through the coating is taken as a measure of its scrub resistance.

If a reference coating is used, the number of cycles needed to wear through the test coating is expressed as a percentage of the number of cycles needed to wear through the reference coating.

 

Choice of Method

In some cases the test method will be specified but in others it is necessary to choose the most appropriate one. In our opinion the advantages and limitations of the methods described on this page are as follows:-

 

 

Method	Advantages	Limitations
BS EN ISO 11998	The most reproducible of the three methods. The reason is that it involves measuring loss of film weight rather than the number of cycles needed to wear through the film. The reproducibility of "wear-though" methods is compromised by the difficulty in preparing films of very similar film thickness.	No serious limitations.
DIN 53778: Part 2	Requires the least operator attention during the course of the test.	Not a very severe test and consequently can take a long time wear through the coating.
ASTM D 2486	A fairly severe test and consequently it does not usually take very long for the coating to wear through.	Requires the most operator attention during the course of the test.

 

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 these tests.

 

Please contact Peter Collins for further details.

 

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