Determination of Spreading Rate

BS 3900-A16 : ISO 7254

 Spreading Rate

Scope and Field of Application

BS 3900-A16 and ISO 7254 are alternative names for the same method which is designed to measure the natural spreading rate of application of a liquid paint or coating when applied to a surface using a brush.

The standard defines "natural spreading rate" as the area covered by a given weight (or volume) of coating when applied uniformly by a skilled operator to give a film free of runs, sags and tears. The value (which is expressed as square metres per kilo or square metres per litre) is often quoted on the product label since it is a useful indication of how much coating needs to be purchased for a given project.

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.

BS 3900-A17 / ISO 7877 is a related standard. It does not involve the measurement of any coating properties but describes how to coat test panels at a specified spreading rate.

Summary of Method

A quantity of the coating is transferred to a suitable container and then weighed, together with a brush, to the nearest 10 mg. An experienced painter then applies the coating to a 300 x 600 mm test panel. The brush plus the container are then re-weighed. Since the weight of the coating used and the area covered are both known, the spreading rate can be expressed in square metres per kilo. A density determination on the paint will enable the spreading rate to be calculated in square metres per litre.

There are a number of factors that can affect the spreading rate including temperature, relative humidity, the nature the test panel, its porosity, whether or not it has been primed and whether it is vertical or horizontal when coated. All of these are subject to agreement between interested parties and should be recorded.

Any solvent that evaporates from the coating in the container during the test will result in an erroneously low value for the spreading rate. Consequently the method is not suitable for coatings which contain highly volatile solvents.

Sample Requirements

We require 1 litre of coating.

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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