ASTM D5795-95(2008)
(Test Method)Standard Test Method for Determination of Liquid Water Absorption of Coated Hardboard and Other Composite Wood Products Via
“Cobb Ring” Apparatus
Standard Test Method for Determination of Liquid Water Absorption of Coated Hardboard and Other Composite Wood Products Via<br> <span class='unicode'>“</span>Cobb Ring<span class='unicode'>”</span> Apparatus
SIGNIFICANCE AND USE
This test method provides a simple quantitative measure of water absorption by coated composite wood products. Although primarily used to evaluate factory-primed composite wood products, this test method may be of service for other wood substrates and coating systems.
This test method has demonstrated utility for composite wood siding products ranging in thickness from approximately 6.35 to 25.4 mm (¼ to 1 in.). Extension of this test method to wood substrates of other types and thickness may be useful.
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.
Such measurements are used as indicators or predictors of the anticipated performance of coated composite wood 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 composite wood 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 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D5795 − 95 (Reapproved2008)
Standard Test Method for
Determination of Liquid Water Absorption of Coated
Hardboard and Other Composite Wood 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 3.1.2 Cobb unit (C.U.) factor, n—a dimensionless math-
ematical term which, for a given ring size, may be multiplied
1.1 This test method is intended to serve as a means for
times the weight change after 24 h to calculate the Cobb unit
measurement of liquid water that passes through a wetted paint
value.
film, and which is subsequently absorbed and retained by the
3.1.2.1 Discussion—The C.U. factor is calculated as fol-
underlying wood substrate. Alternative techniques for the use
lows:
of the “Cobb Ring” apparatus are described.
100 100
1.2 The values stated in SI units are to be regarded as the
C.U. Factor 5 5 (1)
Area ring πr
~ !
standard. The values given in parentheses are for information
only. where:
r = radius
1.3 This standard does not purport to address all of the
For example, for 101.6-mm (4-in.) inside diameter ring.
safety concerns, if any, associated with its use. It is the
or
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 100 100
C.U. Factor 5 5 5 7.96 (2)
3.14 2 12.56
bility of regulatory limitations prior to use. ~ !
3.1.3 composite wood products, n—boards or other struc-
2. Referenced Documents
tured or decorative materials manufactured from wood fibers,
flakes or strands and various resin binders.
2.1 ASTM Standards:
3.1.3.1 Discussion—One example is hardboard.
D1193 Specification for Reagent Water
E177 Practice for Use of the Terms Precision and Bias in 3.1.4 hardboard—a generic term for a panel manufactured
ASTM Test Methods primarily from interfelted lignocellulose fibers consolidated
E691 Practice for Conducting an Interlaboratory Study to under heat and pressures in a hot press to density of at least 31
Determine the Precision of a Test Method lbs (13.95 kg) per cubic foot (cubic metre).
4. Summary of Test Method
3. Terminology
4.1 Suitable size rings of metal or plastic are adhered or
3.1 Definitions of Terms Specific to This Standard:
clampedtotheflat,coatedsurfaceofcompositewoodpanelsto
3.1.1 Cobb unit (C.U.), n—The weight of distilled water
be tested.
absorbed by the underlying wood substrate in grams per 645
2 2
4.2 The assembly is equilibrated at a constant temperature
cm (100 in. ) of surface area (discounting additional areas
and humidity and weighed.
contributed by texturing or grooves) per 24-h time period.
4.3 The weighed assembly is placed on horizontal surface
in a controlled temperature and humidity room or environmen-
tal chamber. Water is placed in the ring and left in contact with
This test method is under the jurisdiction of ASTM Committee D01 on Paint
and Related Coatings, Materials, andApplications and is the direct responsibility of
the board face for 24 h.
Subcommittee D01.52 on Factory Coated Wood Products.
Current edition approved June 1, 2008. Published June 2008. Originally
approved in 1995. Last previous edition approved in 2000 as D5795 - 95 (2000). “Today’s Hardboard,” American Hardboard Association, 1210 W. Northwest
DOI: 10.1520/D5795-95R08. Highway, Palatine, IL 60067.
2 4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or The specification of a solid, continuous horizontal surface or a discontinuous
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM (wire rack, expanded metal, etc.) is required. Surface must be consistent from
Standards volume information, refer to the standard’s Document Summary page on laboratory to laboratory since this can influence the rate of evaporation of moisture
the ASTM website. and, thus, retention of moisture and Cobb values.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5795 − 95 (2008)
4.4 After24htheremainingwaterisremovedfromthering, 7.4 Control Samples, coated or uncoated without rings will
the assembly blotted dry and reweighed. also be required. These will be used to assess the degree of
equilibration that is achieved.
4.5 The increase in weight of the assembly due to water
uptake is calculated by simple subtraction and then converted
8. Hazards
to Cobb units through the use of the C.U. factor (see 3.1.2).
8.1 Use saws with goggles, dust mask, and proper machine
5. Significance and Use safeguards to prevent injury.
5.1 This test method provides a simple quantitative measure 8.2 Caulking compounds may be flammable and contain
of water absorption by coated composite wood products. toxic solvents. See manufacturer’s instructions for proper use
Although primarily used to evaluate factory-primed composite and disposal.
wood products, this test method may be of service for other
9. Procedure
wood substrates and coating systems.
9.1 Sealing of Rings to the Coated Face of the Samples:
5.2 This test method has demonstrated utility for composite
9.1.1 A continuous bead of caulk is applied to one edge of
wood siding products ranging in thickness from approximately
1 the ring. The caulked side of the ring is then attached to the
6.35 to 25.4 mm ( ⁄4 to 1 in.). Extension of this test method to
sample with gentle pressure and a slight twisting motion; to
wood substrates of other types and thickness may be useful.
maintain an accurate and uniform test area, only minor caulk
5.3 Conditioning of substrate, coated sample preparation,
“squeeze-out” should occur inside of the ring. Carefully wipe
application method, dry film thickness, cure conditions, and
out this minor caulk“ squeeze-out” to prevent errors in later
number of replicate specimens should be agreed upon between
calculations.
the purchaser and the supplier of the coating material.
9.1.2 Alternatively, the assembly may be produced with a
5.4 Such measurements are used as indicators or predictors
clamp and gasket device. Satisfactory results can also be
of the anticipated performance of coated composite wood
obtained from clamp and gasket devices that are of self design
products during exterior exposure. They may be used for
and locally produced by any machine shop.
developmentalevaluationofcoatings,substrates,orboth.They
9.1.3 To enhance reproducibility, do not generate data by a
may also be useful for quality control or monitoring of the
combination of the caulk procedure and the clamp and gasket
production of coated composite wood products. procedure.
9.1.4 Also,forimprovedreproducibility,allringsmustbeof
6. Apparatus
the same nominal internal diameter.
6.1 Rings, may be cut from stainless steel, aluminu
...
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