An ASTM International committee is in the process of developing a standard that will provide a visual rating guideline on the degree of water beading in architectural coatings, an alternative method of evaluation to using precise imaging equipment.
Water beading is an aesthetic effect sometimes recognized as a product feature by architectural coatings manufacturers who produce water-repellent wood finishes and deck stains, ASTM said.
While water beading on a coated surface can be measured through the use of a microscopic imaging system (ASTM D7334, Practice for Surface Wettability of Coatings, Substrates and Pigments by Advancing Contact Angle Measurement), the organization says it is not always critical to evaluate bead formation with this level of precision.
As a result, ASTM WK32143, Test Method for Visual Assessment of Water Beading on Horizontal Coatings, is being developed by Subcommittee D01.42 on Architectural Coatings, part of ASTM Committee D01 on Paint and Related Coatings, Materials and Applications.
The test described in ASTM WK32143 can be repeated after coated specimens have been submitted to intervals of aging or weathering, thereby demonstrating the persistence of the coating’s ability to bead water, the organization said.
“The proposed standard will be helpful because it provides coating formulators with a simple and standard tool to compare and optimize water-beading characteristics,” said Neal Rogers, a D01.42 member and group leader, new product development, coatings research and development, Cook Composites and Polymers. Rogers also noted that coating formulators will be the primary users of ASTM WK32143.
“The formulators are likely to represent manufacturers of architectural paints or paint additives,” Rogers said. “Although the proposed standard is being developed from an architectural coating point of view, rating of the visual effect of water beading could also be applied to any horizontal coating system.”
The organization welcomes participation in the standards development process.
“Specific to ASTM WK32143, it would be of interest to add the perspectives of those who manufacture additives to enhance water beading or water repellency characteristics of coatings,” Rogers added.
More information: www.astm.org