ASTM D7868-21

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Designation: D7868 − 13 (Reapproved 2017) D7868 − 21
Standard Practice for
Determining the Dry Fall (Fog) Properties of Protective
Coatings
This standard is issued under the fixed designation D7868; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers a procedure for qualitatively evaluating the dry fall properties of coatings. The establishment of the test
environment and the evaluation procedures are described.
1.2 This practice uses panels containing an automotive finish since these types of surfaces are often the primary concern relating
to overspray damage. Panels coated with other systems may be used as collection surfaces when they are deemed to be more
representative.
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D610 Practice for Evaluating Degree of Rusting on Painted Steel Surfaces
D5402 Practice for Assessing the Solvent Resistance of Organic Coatings Using Solvent Rubs
3. Terminology
3.1 Definitions:
3.1.1 dry/fall/fog dry fall/fog coating, n—an interior or exterior coating specially formulated so that the fine particles of overspray
dry to a dust or powder during a free fall of a certain distance at specific temperature and humidity ranges, and will not adhere
to surfaces on which the overspray is subsequently deposited.
This practice is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.46 on Industrial Protective Coatings.
Current edition approved Dec. 1, 2017Nov. 1, 2021. Published December 2017November 2021. Originally approved in 2013. Last previous edition approved in 20132017
as D7868 – 13. 13 (2017). DOI: 10.1520D7868-13R17.10.1520D7868-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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D7868 − 21
4. Summary of Practice
4.1 A structural frame is erected and enclosed. enclosed unless a dry fall/fog test chamber or laboratory space is pre-designated.
Spray targets are placed at the top, inside the enclosure. Four steel panels coated with an automotive basecoat/clear coat system
are placed on the enclosure floor to collect the dry fall. (Panels coated with other systems or uncoated panels, or both, can be used
when they are deemed to be more representative.) A duplicate panel set is maintained at the prevailing air temperature, while the
other duplicate panel set is heated in oven and placed inside the enclosure immediately prior to atomizing the coating. The coating
is atomized against the targets at each of two distances and the panels are removed for evaluation. Two of the coated steel panels
remain at laboratory ambient conditions, while the “pre-heated” panels are returned to a laboratory oven. The heated and ambient
coated panels are cleaned and evaluated after 24-h for dry fall attachment.
5. Significance and Use
5.1 Attachment of overspray particles to vehicles and other surfaces not intended to be coated can result in property damage and
insurance claims. Dry fall coatings are formulated such that overspray particles dry as they move through the air, and before they
land on horizontal surfaces. These particles can then be brushed off, vacuumed or washed from the surfaces with no damage. This
practice can be used to evaluate the dry fall properties of coatings prior to large scale use. The practice can also be used to evaluate
whether the coating(s) possess the same dry fall properties when the fallout collects on surfaces with an elevated temperature.
FIG. 1 Dry Fall Evaluation
Enclosure with Plastic Sheeting
(Note—Base is heightened using 1.5 in. wooden blocks.)
D7868 − 21
6. Reagents
6.1 Commercially available Car Washing Concentrate.
6.2 Mineral Spirits.
7. Procedure
7.1 Construct a frame (enclosure) using steel conduit and couplings or other materials of construction. The interior of the enclosure
measures approximately 3 ft wide by 4 ft deep and is 19 approximately 20 ft high in order to permit a dry fall test distance of 18
ft. Enclose the frame with plastic sheeting or tarpaulins and secure, making sure there is access at the base of the enclosure to
add and remove the collection surfaces (coated panels). A base constructed of plywood and protected with paper or plastic sheeting
(that can be pushed in/pulled out to load/unload the panels) may be used. This requires the frame to be heightened approximately
2 in. from the floor surface using wooden blocks or other methods (see Fig. 1).
7.2 Fabricate and suspend (vertically) a spray target constructed of ⁄8 in. by 3 by 3 ft wood or other rigid material onto two
hanging rods inside the enclosure. Mount troughs along the bottom edge of the target (optional) or position the collection surfaces
to prevent dripping coating on the dry fall collection surfaces at the base of the enclosure. The spray targets are positioned at the
top of the enclosure to allow a dry fall distance of 18 ft, and are positioned 48 ftin. and 24 ftin. from the spray gun tip (see 7.7
and 7.9). The spray targets shall be replaced for each test to prevent build-up of wet coating on the targets and potential dripping
onto the dry fall collection surfaces at the base of the enclosure (See(see Fig. 2).
7.3 Mix and reduce (thin) the coating material according to the manufacturer’s instructions, by the maximum amount permitted.
Record the material temperature. Atomize the coating by airless spray (unless another spray method is mutually selected), using
the pump pressure, hose diameter and tip size recommended by the manufacturer. If the coating manufacturer recommends a range
of pump pressures and tip sizes, use the lowest pump pressure and the largest tip size (of the ranges recommended) to create a
worse case scenario. Record the actual
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