ASTM D5795-16(2024)

Standard Test Method for Determination of Liquid Water Absorption of Coated Wood and Wood Based Products Via “Cobb Ring” Apparatus

SIGNIFICANCE AND USE
5.1 This test method provides a simple quantitative measure of water absorption by coated wood or wood based products.  
5.2 This test method has demonstrated utility for wood or wood based products ranging in thickness from approximately 6 mm to 25 mm (1/4 in. to 1 in.).  
5.3 Conditioning of substrate, coated sample preparation, application method, dry film thickness, cure conditions, and number of replicate specimens should be agreed upon between the purchaser and the supplier of the coating material.  
5.4 Such measurements are used as indicators or predictors of the anticipated performance of coated wood or wood based products during exterior exposure. They may be used for developmental evaluation of coatings, substrates, or both. They may also be useful for quality control or monitoring of the production of coated wood and wood based products.
SCOPE
1.1 This test method is intended to serve as a means for measurement of liquid water that passes through a wetted paint film, and which is subsequently absorbed and retained by the underlying wood or wood-based substrate. Alternative techniques for the use of the “Cobb Ring” apparatus are described.  
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.3 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.  
1.4 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.

General Information

• Status: Published
• Publication Date: 31-Jan-2024
• ICS: 79.060.01 - Wood-based panels in general
• Technical Committee: D01 - Paint and Related Coatings, Materials, and Applications
• Drafting Committee: D01.52 - Factory Coated Wood Products

Relations

• Replaces: ASTM D5795-16 - Standard Test Method for Determination of Liquid Water Absorption of Coated Wood and Wood Based Products Via “Cobb Ring” Apparatus
• Effective Date: 01-Feb-2024
• Refers: ASTM D5235-18(2024) - Standard Test Method for Microscopic Measurement of Dry Film Thickness of Coatings on Wood Products
• Effective Date: 01-Feb-2024
• Refers: ASTM D5235-18 - Standard Test Method for Microscopic Measurement of Dry Film Thickness of Coatings on Wood Products
• Effective Date: 15-Jan-2018
• Referred By: ASTM D7433-19 - Standard Test Method for Measuring Surface Water Absorption of Overlaid Wood-Based Panels
• Effective Date: 01-Feb-2024

Overview

ASTM D5795-16(2024) is an international standard developed by ASTM International that establishes a test method for determining the liquid water absorption of coated wood and wood-based products using the “Cobb Ring” apparatus. This test method offers a practical, quantitative approach to understanding water permeability through coatings and into wood substrates. The standard applies to products with thicknesses between approximately 6 mm and 25 mm, covering a wide range of wood and engineered wood panels used in construction and manufacturing.

By quantifying water absorption, organizations can better evaluate the protective quality of coatings on wood products, informing decision-making for product development, quality control, and performance prediction during exterior exposure.

Key Topics

• Water Absorption Measurement: The main focus is to measure the quantity of liquid water that passes through a painted or coated surface and is absorbed by the underlying wood using the Cobb Ring method.
• Cobb Ring Apparatus: This apparatus allows for a standardized test area and water depth, ensuring comparable results across laboratories and products.
• Conditioning and Sample Preparation: The standard outlines the importance of consistent sample conditioning, preparation methods, and agreement between suppliers and purchasers regarding variables like coating application, curing, and film thickness.
• Quantitative Results: Water absorption is reported in "Cobb units," providing objective data that facilitates product comparison and process optimization.
• Test Reliability: The standard references procedures to improve accuracy, including minimum numbers of replicates and environmental controls for repeatable and reproducible results.

Applications

The ASTM D5795-16(2024) standard is valuable in a variety of contexts involving coated wood and engineered wood products:

• Product Development: Manufacturers use this method to evaluate coatings and substrates in research and development, comparing resistance to liquid water penetration among different formulations.
• Quality Control: Routine use of the Cobb Ring test helps monitor and maintain the consistency of coated wood production, identifying potential issues before large-scale deployment.
• Performance Prediction: Results from this method serve as indicators for how coated wood products are likely to perform during outdoor or exterior exposure, informing maintenance schedules and warranty periods.
• Supplier-Purchaser Agreement: The standard provides a basis for negotiating test conditions and acceptance criteria in supply agreements, enhancing communication and mutual understanding regarding product performance.
• Regulatory Compliance: Following ASTM standards assists companies in demonstrating due diligence and product reliability, potentially supporting claims in environmentally sensitive or safety-focused markets.

Related Standards

This standard references several related ASTM documents crucial for implementing consistent and reliable testing:

• ASTM D9: Terminology relating to wood and wood-based products
• ASTM D16: Terminology for paint, related coatings, materials, and applications
• ASTM D1193: Specification for reagent water
• ASTM D5235: Test method for microscopic measurement of dry film thickness of coatings on wood products
• ASTM D6132: Test method for nondestructive measurement of dry film thickness of applied organic coatings using ultrasonic gauges
• ASTM E177 and ASTM E691: Practices governing precision, bias, and interlaboratory studies

Keywords

absorption, Cobb ring, water absorption, coated wood, composite wood, wood-based products, test method, ASTM D5795, coatings, quality control, performance test, standardization

By utilizing ASTM D5795-16(2024), stakeholders in the wood and coatings industries can ensure reliable, comparable data on water resistance, supporting product innovation, regulatory compliance, and customer satisfaction.

Standards Content (Sample)

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.
Designation: D5795 − 16 (Reapproved 2024)
Standard Test Method for
Determination of Liquid Water Absorption of Coated Wood
and Wood Based Products Via “Cobb Ring” Apparatus
This standard is issued under the fixed designation D5795; 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 Ultrasonic Coating Thickness Gage
E177 Practice for Use of the Terms Precision and Bias in
1.1 This test method is intended to serve as a means for
ASTM Test Methods
measurement of liquid water that passes through a wetted paint
E691 Practice for Conducting an Interlaboratory Study to
film, and which is subsequently absorbed and retained by the
Determine the Precision of a Test Method
underlying wood or wood-based substrate. Alternative tech-
niques for the use of the “Cobb Ring” apparatus are described.
3. Terminology
1.2 The values stated in SI units are to be regarded as the
3.1 Definitions of Terms Specific to This Standard:
standard. The values given in parentheses are for information
3.1.1 Cobb unit (C.U.), n—the weight of distilled water
only.
absorbed by the underlying wood substrate in grams per 645
1.3 This standard does not purport to address all of the 2 2
cm (100 in. ) of surface area (discounting additional areas
safety concerns, if any, associated with its use. It is the
contributed by texturing or grooves) per 24-h time period.
responsibility of the user of this standard to establish appro-
3.1.2 Cobb unit (C.U.) factor, n—a dimensionless math-
priate safety, health, and environmental practices and deter-
ematical term which, for a given ring size, may be multiplied
mine the applicability of regulatory limitations prior to use.
times the weight change after 24 h to calculate the Cobb unit
1.4 This international standard was developed in accor-
value.
dance with internationally recognized principles on standard-
3.1.2.1 Discussion—The C.U. factor is calculated as fol-
ization established in the Decision on Principles for the
lows:
Development of International Standards, Guides and Recom-
SI Units
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 64516 64516
C.U.Factor 5 5 (1)
2 2
RingArea mm πr
~ !
2. Referenced Documents Imperial Units
2.1 ASTM Standards: 100 100
C.U.Factor 5 5 (2)
2 2
D9 Terminology Relating to Wood and Wood-Based Prod- RingArea~in. ! πr
ucts
where:
D16 Terminology for Paint, Related Coatings, Materials, and
r = radius, mm (in.)
Applications
For example, for 100 mm (4 in.) inside diameter or 50 mm
D1193 Specification for Reagent Water
(2 in.) internal radius ring:
D5235 Test Method for Microscopic Measurement of Dry
Film Thickness of Coatings on Wood Products
64516 64516
C.U. Factor 5 2 2 8.22 (3)
D6132 Test Method for Nondestructive Measurement of Dry 2
3.14 50! 7850
~
Film Thickness of Applied Organic Coatings Using an
3.1.3 wood based products, n—boards or other form of
structured or decorative materials manufactured from wood
fibers, flakes or strands or veneers and various resin binders
This test method is under the jurisdiction of ASTM Committee D01 on Paint
otherwise known as engineered wood products or wood
and Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.52 on Factory Coated Wood Products.
composite.
Current edition approved Feb. 1, 2024. Published February 2024. Originally
approved in 1995. Last previous edition approved in 2016 as D5795 – 16. DOI:
4. Summary of Test Method
10.1520/D5795-16R24.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4.1 Suitable size rings of metal or plastic are adhered or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
clamped to the flat, coated surface of composite wood panels to
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. be tested.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5795 − 16 (2024)
4.2 The assembly is equilibrated at a constant temperature 6.5 Balance, with sufficient capacity (typically 400 g) and
and humidity and weighed. 0.01 g accuracy.
4.3 The weighed assembly is placed on horizontal surface
7. Materials
in a controlled temperature and humidity room or environmen-
7.1 Butyl or Silicone Caulk, which has been determined not
tal chamber. Water is placed in the ring and left in contact with
to contribute to assembly weight change through absorption of
the board face for 24 h.
water or interaction with the coating.
4.4 After 24 h the remaining water is removed from the ring,
7.2 Distilled Water, (see Specification D1193).
the assembly blotted dry and reweighed.
7.3 Test Boards, appropriately identified, coated or
4.5 The increase in weight of the assembly due to water
uncoated, cut to a square size that is 25.4 mm (1 in.) greater
uptake is calculated by simple subtraction and then converted
than the ring diameter. A minimum of three replicates is
to Cobb units through the use of the C.U. factor (see 3.1.2).
recommended.
5. Significance and Use
7.4 Control Samples, coated or uncoated without rings will
also be required. These will be used to assess the degree of
5.1 This test method provides a simple quantitative measure
equilibration that is achieved.
of water absorption by coated wood or wood based products.
8. Hazards
5.2 This test method has demonstrated utility for wood or
wood based products ranging in thickness from approximately
8.1 Use saws with goggles, dust mask, and proper machine
6 mm to 25 mm ( ⁄4 in. to 1 in.).
safeguards to prevent injury.
5.3 Conditioning of substrate, coated sample preparation,
8.2 Caulking compounds may be flammable and contain
application method, dry film thickness, cure conditions, and
toxic solvents. See manufacturer’s instructions for proper use
number of replicate specimens should be agreed upon between
and disposal.
the purchaser and the supplier of the coating material.
9. Procedure
5.4 Such measurements are used as indicators or predictors
9.1 Measure and record the coating thickness on the
of the anticipated performance of coated wood or wood based
samples designated for testing, including thickness of indi-
products during exterior exposure. They may be used for
vidual coats (if distinguishable). Follow procedures described
developmental evaluation of coatings, substrates, or both. They
in Test Methods D5235 or D6132 (if applicable).
may also be useful for quality control or monitoring of the
production of coated wood and wood based products.
9.2 Sealing of Rings to the Coated Face of the Samples:
9.2.1 A continuous bead of caulk is applied to one edge of
6. Apparatus
the ring. The caulked side of the ring is then attached to the
6.1 Rings, may be cut from stainless steel, aluminum or sample with gentle pressure and a slight twisting motion; to
plastic pipes. To avoid damage to the test assembly caused by maintain an accurate and uniform test area, only minor caulk
warping of the wooden substrate due to water absorption on “squeeze-out” should occur inside of the ring. Carefully
one side only, it is recommended to use flexible rings. Measure remove this minor caulk “squeeze-out” to prevent errors in
the rings diameter to the nearest 1 mm (0.040 in.). later calculations. Care must be taken not to smear caulk over
NOTE 1—The ring diameter can be any size, but useful results have been
the coating surface to avoid invalidating results. Consider the
obtained with rings of 102 mm (4 in.) or larger inside diameter, wall
use of caulks with contrasting colors to aid in verification of
thickness of 10 mm ( ⁄8 in.) and height of 25 mm (1 in.). Rings of 100 mm
removal. If flexible rings are used, they should be supported
to 254 mm (4 in. to 10 in.) are commonly used. If suitable flexible rings
from the inside by a segment of rigid pipe with the appropriate
cannot be
...