ASTM D5795-95(2000)
(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 "Cobb Ring" 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 is subsequently absorbed and retained by the underlying wood substrate. Alternative techniques in the use of the "Cobb Ring" apparatus are described.
1.2 The values stated in inch-pound 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(Reapproved2000)
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 D 5795; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.2.1 Discussion—The C.U. factor is calculated as fol-
lows:
1.1 This test method is intended to serve as a means for
measurement of liquid water that passes through a wetted paint 100 100
C.U. Factor 5 5 (1)
film, and which is subsequently absorbed and retained by the Area ~ring!
pr
underlying wood substrate. Alternative techniques for the use
where:
of the “Cobb Ring” apparatus are described.
r = radius
1.2 The values stated in SI units are to be regarded as the
For example, for 101.6-mm (4-in.) inside diameter ring.
standard. The values given in parentheses are for information
or
only.
100 100
1.3 This standard does not purport to address all of the
C.U. Factor 5 5 5 7.96 (2)
12.56
3.14~2!
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.1.3 composite wood products—boards or other structured
priate safety and health practices and determine the applica-
or decorative materials manufactured from wood fibers, flakes
bility of regulatory limitations prior to use.
or strands and various resin binders.
3.1.3.1 Discussion—One example is hardboard.
2. Referenced Documents
3.1.4 hardboard—a generic term for a panel manufactured
2.1 ASTM Standards:
primarily from interfelted lignocellulose fibers consolidated
D 1193 Specification for Reagent Water
under heat and pressures in a hot press to density of at least 31
E 177 Practice for the Use of the Terms Precision and Bias
lbs (13.95 kg) per cubic foot (cubic meter).
in ASTM Test Methods
4. Summary of Test Method
E 691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
4.1 Suitable size rings of metal or plastic are adhered or
clampedtotheflat,coatedsurfaceofcompositewoodpanelsto
3. Terminology
be tested.
3.1 Definitions of Terms Specific to This Standard:
4.2 The assembly is equilibrated at a constant temperature
3.1.1 Cobb unit (C.U.), n—The weight of distilled water
and humidity and weighed.
absorbed by the underlying wood substrate in grams per 645
4.3 The weighed assembly is placed on horizontal surface
2 2
cm (100 in. ) of surface area (discounting additional areas
in a controlled temperature and humidity room or environmen-
contributed by texturing or grooves) per 24-h time period.
tal chamber. Water is placed in the ring and left in contact with
3.1.2 Cobb unit (C.U.) factor, n—a dimensionless math-
the board face for 24 h.
ematical term which, for a given ring size, may be multiplied
4.4 After24htheremainingwaterisremovedfromthering,
times the weight change after 24 h to calculate the Cobb unit
the assembly blotted dry and reweighed.
value.
1 4
This test method is under the jurisdiction of ASTM Committee D-1 on Paint “Today’s Hardboard”, American Hardboard Association, 1210 W. Northwest
and Related Coatings, Materials, andApplications and is the direct responsibility of Highway, Palatine, IL 60067.
Subcommittee D01.52 on Factory-Coated Wood Products. The specification of a solid, continuous horizontal surface or a discontinuous
Current edition approved Oct. 10, 1995. Published December 1995. (wire rack, expanded metal, etc.) is required. Surface must be consistent from
Annual Book of ASTM Standards, Vol 11.01. laboratory to laboratory since this can influence the rate of evaporation of moisture
Annual Book of ASTM Standards, Vol 14.02. 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 (2000)
4.5 The increase in weight of the assembly due to water 8.2 Caulking compounds may be flammable and contain
uptake is calculated by simple subtraction and then converted toxic solvents. See manufacturer’s instructions for proper use
to Cobb units through the use of the C.U. factor (see 3.1.2 ). and disposal.
5. Significance and Use
9. Procedure
5.1 This test method provides a simple quantitative measure
9.1 Sealing of Rings to the Coated Face of the Samples:
of water absorption by coated composite wood products.
9.1.1 A continuous bead of caulk is applied to one edge of
Although primarily used to evaluate factory-primed composite
the ring. The caulked side of the ring is then attached to the
wood products, this test method may be of service for other
sample with gentle pressure and a slight twisting motion; to
wood substrates and coating systems.
maintain an accurate and uniform test area, only minor caulk
5.2 This test method has demonstrated utility for composite
“squeeze-out” should occur inside of the ring. Carefully wipe
wood siding products ranging in thickness from approximately
out this minor caulk“ squeeze-out” to prevent errors in later
6.35 to 25.4 mm ( ⁄4 to 1 in.). Extension of this test method to
calculations.
wood substrates of other types and thickness may be useful.
9.1.2 Alternatively, the assembly may be produced with a
5.3 Conditioning of substrate, coated sample preparation,
clamp and gasket device. Satisfactory results can also be
application method, dry film thickness, cure conditions, and
obtained from clamp and gasket devices that are of self design
number of replicate specimens should be agreed upon between
and locally produced by any machine shop.
the purchaser and the supplier of the coating material.
9.1.3 To inhance reproducibility, do not generate data by a
5.4 Such measurements are used as indicators or predictors
combination of the caulk procedure and the clamp and gasket
of the anticipated performance of coated composite wood
procedure.
products during exterior exposure. They may be used for
9.1.4 Also,forimprovedreproducibility,allringsmustbeof
developmentalevaluationofcoatings,substrates,orboth.They
the same nominal internal diameter.
may also be useful for quality control or monitoring of the
9.2 Equilibration:
production of coated composite wood products.
9.2.1 Allow the samples with rings and controls without
rings to equilibrate for seven days at 23 6 2°C (73 6 4°F) and
6. Apparatus
50 6 5 % relative humidity.
6.1 Rings, may be cut from stainless steel, aluminum or
9.3 Initial Weighing:
PVC pipe.The ring diameter can be any size, but useful results
6 9.3.1 Weigh (grams) the controls and s
...
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