ASTM C1789-14(2018)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C1789 − 14 (Reapproved 2018)
Standard Test Method for
Calibration of Hand-Held Moisture Meters on Gypsum
Panels
This standard is issued under the fixed designation C1789; 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 C1278/C1278M Specification for Fiber-Reinforced Gypsum
Panel
1.1 This test method applies to the calibration of handheld
C1396/C1396M Specification for Gypsum Board
moisture meters for gypsum board, glass faced gypsum panels
D4442 Test Methods for Direct Moisture Content Measure-
and fiber-reinforced gypsum panels by means of electrical
ment of Wood and Wood-Based Materials
conductance and dielectric meters. The test uses wetted test
D4444 Test Method for Laboratory Standardization and
specimens which are dried down in at least 5 steps to determine
Calibration of Hand-Held Moisture Meters
the moisture content based on the weight loss in comparison to
2.2 ASHRAE Standard:
the dry weight. The test also supplies the ERH values for each
2009 ASHRAE Handbook – Fundamentals, Chapter 1 –
of the drying steps.
Psychrometrics, American Society of Heating, Refrigerat-
1.2 This test method has not been evaluated for the influ-
ing and Air-conditioning Engineers
ence of paint or wall covering materials on the indicated
moisture content of a gypsum board or panel substrate. 3. Terminology
1.3 This standard does not purport to address all of the
3.1 Definitions of Terms Specific to This Standard:
safety concerns, if any, associated with its use. It is the 3.1.1 absolute humidity, d , n—the ratio of the mass of water
v
responsibility of the user of this standard to establish appro-
vapor to the total volume of the moist air sample.
priate safety, health, and environmental practices and deter-
3.1.2 admittance, n—inverse of impedance, a measure of
mine the applicability of regulatory limitations prior to use.
how easily an electric current can flow through a material.
1.4 This international standard was developed in accor-
3.1.3 conductance meters, n—conductance meters are those
dance with internationally recognized principles on standard-
that measure predominantly ionic conductance between points
ization established in the Decision on Principles for the
of applied voltage, usually dc.
Development of International Standards, Guides and Recom-
3.1.3.1 Discussion—Conductance meters generally have
mendations issued by the World Trade Organization Technical
pins that penetrate into the material being measured. Direct-
Barriers to Trade (TBT) Committee.
current conductance meters are commonly referred to as
"resistance" meters. Most commercial conductance meters are
2. Referenced Documents
12 4
high-input impedance (about 10 Ω), wide-range (10 to
2.1 ASTM Standards:
10 Ω) ohmmeters. Their scales are generally calibrated to
C473 Test Methods for Physical Testing of Gypsum Panel
read directly in moisture content (oven-dry mass basis) for a
Products
particular calibration material and at a specific reference
C1177/C1177M Specification for Glass Mat Gypsum Sub-
temperature.
strate for Use as Sheathing
3.1.4 dew-point temperature, t , n—the temperature at
d
C1178/C1178M Specification for Coated Glass Mat Water-
which a sample of moist air being cooled at constant pressure
Resistant Gypsum Backing Panel
and moisture content reaches 100 % relative humidity.
3.1.4.1 Discussion—The dew-point temperature is the tem-
perature at which water condensation begins to occur on a
This test method is under the jurisdiction of ASTM Committee C11 on Gypsum
and Related Building Materials and Systems and is the direct responsibility of
cooled surface in contact with moist air.
Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products.
3.1.5 dielectric meters, n—meters that measure primarily by
Current edition approved Oct. 1, 2018. Published October 2018. Originally
approved in 2013. Last previous edition approved in 2014 as C1789 – 14. DOI: admittance or power loss.
10.1520/C1789-14R18.
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 Available from American Society of Heating, Refrigerating, and Air-
Standards volume information, refer to the standard’s Document Summary page on Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA
the ASTM website. 30329, http://www.ashrae.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1789 − 14 (2018)
3.1.5.1 Discussion—Dielectric meters generally do not have 4.2 The calibration is based on the MC of the test specimen.
pins that penetrate into the material being measured. There are The corresponding ERH is determined by use of a calibrated
two general types of dielectric meters that may be arbitrarily direct read relative humidity meter.
categorized by their predominant mode of response – admit-
4.3 ERH is essentially equivalent to water activity Aw
tance (or capacitance) and power loss. Both have surface
which is a measure of the amount of moisture in a material that
contact electrodes and readout scales that are usually marked in
is available to impact the performance characteristics of that
arbitrary units. Most dielectric meters operate in the r-f
material.
frequency range, generally between 1 and 10 MHz. Admittance
4.4 Due to the various core and/or facing additives that are
meters respond primarily to the capacitance (dielectric con-
used to modify the moisture absorption characteristics, strength
stant) of the material being measured. Power loss meters react
and/or other properties for specific applications, a separate
primarily to the resistance of the material. Readings of dielec-
calibration is required for each type of gypsum board or panel
tric meters are significantly affected by the relative density
to be measured.
(specific gravity) of the specimen material.
4.5 The test method has the following steps:
3.1.6 equilibrium moisture content, EMC, n—the moisture
content of a material that is in thermodynamic equilibrium with 4.5.1 Measure the dry weights of the test specimens.
the surrounding air at a given temperature and relative humid-
4.5.2 Determine the time step for the drying intervals that
ity.
will provide sufficient data points to develop a calibration
curve.
3.1.7 equilibrium relative humidity, ERH—the relative hu-
4.5.3 Saturate the samples with water.
midity of the air in a sealed chamber that is in thermodynamic
4.5.4 Dry the samples in steps, recording after each interval
equilibrium with a sample of material in that chamber.
the moisture content by weight of each sample and the
3.1.8 humidity ratio, W, n—the ratio of the mass of water
temperature, relative humidity (ERH), and absolute humidity
vapor to the mass of dry air contained in a sample of moist air.
of the atmosphere in moisture equilibrium with each sample.
3.1.9 moisture content, MC, n—the ratio of the mass of
water in a material to the oven-dry mass of the sample
5. Significance and Use
expressed as a decimal fraction or percentage.
5.1 This Standard Test Method is intended for use in
3.1.9.1 Discussion—Oven-dry refers to the removal by heat-
calibrating hand-held meters to accurately read from approxi-
ing of all adsomcrbed and free water in the interstitial pores of
mately 30 to 90 % ERH. Moisture content is related to the ERH
the material. Crystalline water such as contained in gypsum
or water activity of a material.
molecules is not included.
5.2 Hand-held meters provide a rapid means of sampling the
3.1.10 relative humidity, ϕ, n—the ratio of the amount of
moisture content of gypsum boards and panels during manu-
water vapor in air to the amount of water vapor in saturated air
facture and for field inspection during and after building
at the same temperature and pressure.
construction. However, these measurements are inferential,
3.1.10.1 Discussion—Equivalent to the ratio of the partial
that is, electrical parameters are measured and compared
pressure of water vapor in the air to the saturated vapor
against a calibration curve to obtain an indirect measure of
pressure at the same temperature and pressure.
moisture content. The electrical measurements are influenced
3.1.11 test uncertainty ratio, TUR, n—comparison between
by the actual moisture content, a number of other gypsum
the accuracy of the Unit Under Test (UUT) and the estimated
board and panel variables, environmental conditions, the ge-
calibration uncertainty stated with a confidence level of 95 %
ometry of the measuring probe, and the design of the meter.
(K=2).
The maximum accuracy can only be obtained by an awareness
3.1.12 water activity, A , n—the ratio of the water vapor
of the effect of each parameter on the meter output and
w
pressure in a material to the vapor pressure of pure water at the
correction of readings as specified by these test methods.
same temperature.
5.3 Electrical conductance and dielectric meters are not
3.1.12.1 Discussion—Water activity is an intrinsic property
necessarily equivalent in their readings under the same condi-
derived from fundamental principles of thermodynamics and
tions. When this test method is referenced, the type of meter
physical chemistry. It is a measure of the energy status of the
that is being used must be reported with the relevant ranges for
water in a system. Commonly used for food preservation
precision and bias as specified in this standard.
analyses, it can be interpreted here as the amount of water in a
5.4 Both types of meters are to be calibrated with respect to
porous material that is available to impact the performance
ERH as described in this standard.
characteristics of the material or to support mold growth.
6. Apparatus
4. Summary of Test Method
6.1 Laboratory equipment for moisture content determina-
4.1 These test methods provide a method for calibrating the
tion by direct method:
scale on conductance and dielectric meters for various types of
gypsum boards and panels for use in field measurement of 6.1.1 Forced Air Oven—Vented electric furnace capable of
moisture content during storage, construction and use in maintaining a steady-state temperature of 45 6 3°C (113 6
building assemblies. 5°F).
C1789 − 14 (2018)
6.1.2 Environmental Chamber—Chamber capable of main- 8.2 Determine the humidity ratio of the trapped environ-
taining a controlled temperature of 20 6 2ºC (68 6 4ºF) and ment that is in moisture equilibrium with each specimen.
relative humidity within the range 30 to 90 6 5 %.
NOTE 2—Humidity ratio is used as the temperature is likely to vary
6.1.3 Electronic Balance or Scale—Electronic scale capable
during the course of the test and relative humidity will vary with
of weighing each test specimen to within 60.10 g
temperature at constant moisture content. Humidity ratio and dew-point
temperature do not vary with temperature at constant moisture content and
(60.0035 oz).
can be calculated from the temperature and relative humidity values
6.1.4 Relative Humidity Test Meter—The meter shall be
measured by direct read instruments.
capable of reading between 30 and 90 % relative humidity. The
8.2.1 Place the specimen in a zip sealed plastic bag to
calibrated test uncertainty ratio (TUR) of this meter shall not be
contain it in a trapped atmosphere.
less than 4:1 over the range of measure cited.
8.2.2 Insert a temperature/relative humidity probe through
6.1.4.1 Meter shall have removable temperature/humidity
the wall of the bag and seal tightly.
probes that can be sealed into sealed plastic bags.
6.1.5 Humidity Box—Insulated box made of materials im-
NOTE 3—Making a small slit in the side of the bag to stretch around the
pervious to water vapor such as plastic or sheet metal, sealed
relative humidity probe has proven to provide a reliable seal.
with a gasketed lid. Open trays of clean, distilled water are
8.2.3 Record the temperature and relative humidity within
positioned in the box so as to keep the atmosphere within the
the bag at one hour intervals.
box saturated with water vapor. Open mesh shelving or racks
8.2.3.1 Calculate the humidity ratio using a psychrometric
are used to support samples above the water.
chart or a table of thermodynamic properties of moist air.
6.1.6 Zip Sealed Plastic Bags—Commercially available
8.2.3.2 Record the dry specimen temperature, relative hu-
plastic freezer weight plastic food storage bag with a zipper
midity and humidity ratio when three consecutive measure-
type closure that seals and prevents water vapor transmission.
ments show no change in humidity ratio as calculated from the
6.1.7 Psychrometric Chart—Graphical presentation of the
meter readings.
thermodynamic properties of moist air.
9. Saturate the Test Specimens
7. Laboratory Calibration
9.1 As the moisture level for physical damage is an ERH of
7.1 This procedure is designed for full-scale calibration of
80 % (A of 0.8) the test specimens must be saturated above
w
the meter. A minimum of 45 calibration specimens shall be
this point as a starting point for calibration. The target
fabricated with a target of ten (10) calibration steps ranging
saturation level is 95 % relative humidity at 20°C (68°F).
from ERH of 30 to 90 %.
NOTE 1—30 % relative humidity represents a practical lower limit on
9.2 Place specimens in a water vapor saturated atmosphere
moisture content found in buildings and the accuracy of readings above
in an environmental chamber or humidity cabinet with relative
90 % relative humidity is problematic. The calibration should not be
humidity equal to or greater than 95 % at 20°C (68°F).
extrapolated below the lowest value tested or above the highest value
9.2.1 Document the environmental chamber conditions us-
tested. Material of the type to be calibrated shall be prepared and tested in
ing a calibrated relative humidity sensor.
a manner that is consistent with the following calibration procedures.
7.2 Specimens shall be free of visible irregularities. 9.3 Maintain specimens in the water saturated atmosphere
until they reach moisture equilibrium with the atmosphere.
7.3 Select a minimum of 45 specimens, each measuring
9.3.1 Maintain specimens in chamber or cabinet until rela-
100 mm wide by 200 mm long (4 by 8 in.), for each given
tive humidity stabilizes at a reading of 95 % or greater.
sample of board or panel.
9.3.2 Remove each specimen and weigh at eight (8) hour
7.3.1 The specimens shall be divid
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1789 − 14 C1789 − 14 (Reapproved 2018)
Standard Test Method for
Calibration of Hand-Held Moisture Meters on Gypsum
Panels
This standard is issued under the fixed designation C1789; 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 test method applies to the calibration of handheld moisture meters for gypsum board, glass faced gypsum panels and
fiber-reinforced gypsum panels by means of electrical conductance and dielectric meters. The test uses wetted test specimens which
are dried down in at least 5 steps to determine the moisture content based on the weight loss in comparison to the dry weight. The
test also supplies the ERH values for each of the drying steps.
1.2 This test method has not been evaluated for the influence of paint or wall covering materials on the indicated moisture
content of a gypsum board or panel substrate.
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 safety, health, and healthenvironmental 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.
2. Referenced Documents
2.1 ASTM Standards:
C473 Test Methods for Physical Testing of Gypsum Panel Products
C1177C1177/C1177M Specification for Glass Mat Gypsum Substrate for Use as Sheathing
C1178C1178/C1178M Specification for Coated Glass Mat Water-Resistant Gypsum Backing Panel
C1278C1278/C1278M Specification for Fiber-Reinforced Gypsum Panel
C1396C1396/C1396M Specification for Gypsum Board
D4442 Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
D4444 Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
2.2 ASHRAE Standard:
2009 ASHRAE Handbook – Fundamentals, Chapter 1 – Psychrometrics, American Society of Heating, Refrigerating and
Air-conditioning Engineers
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 absolute humidity, d , n—the ratio of the mass of water vapor to the total volume of the moist air sample.
v
3.1.2 admittance, n—inverse of impedance, a measure of how easily an electric current can flow through a material.
3.1.3 conductance meters, n—conductance meters are those that measure predominantly ionic conductance between points of
applied voltage, usually dc.
This test method is under the jurisdiction of ASTM Committee C11 on Gypsum and Related Building Materials and Systems and is the direct responsibility of
Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products.
Current edition approved June 1, 2014Oct. 1, 2018. Published July 2014October 2018. Originally approved in 2013. Last previous edition approved in 20132014 as C1789
– 13.14. DOI: 10.1520/C1789-14.10.1520/C1789-14R18.
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.
Available from American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), 1791 Tullie Circle, NE, Atlanta, GA 30329,
http://www.ashrae.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1789 − 14 (2018)
3.1.3.1 Discussion—
Conductance meters generally have pins that penetrate into the material being measured. Direct-current conductance meters are
commonly referred to as "resistance" meters. Most commercial conductance meters are high-input impedance (about 10 Ω),Ω),
4 12
wide-range (10 to 10 Ω) Ω) ohmmeters. Their scales are generally calibrated to read directly in moisture content (oven-dry mass
basis) for a particular calibration material and at a specific reference temperature.
3.1.4 dew-point temperature, t , n—the temperature at which a sample of moist air being cooled at constant pressure and
d
moisture content reaches 100 percent% relative humidity.
3.1.4.1 Discussion—
The dew-point temperature is the temperature at which water condensation begins to occur on a cooled surface in contact with
moist air.
3.1.5 dielectric meters, n—meters that measure primarily by admittance or power loss.
3.1.5.1 Discussion—
Dielectric meters generally do not have pins that penetrate into the material being measured. There are two general types of
dielectric meters that may be arbitrarily categorized by their predominant mode of response – admittance (or capacitance) and
power loss. Both have surface contact electrodes and readout scales that are usually marked in arbitrary units. Most dielectric
meters operate in the r-f frequency range, generally between 1 and 10 MHz. Admittance meters respond primarily to the
capacitance (dielectric constant) of the material being measured. Power loss meters react primarily to the resistance of the material.
Readings of dielectric meters are significantly affected by the relative density (specific gravity) of the specimen material.
3.1.6 equilibrium moisture content, EMC, n—the moisture content of a material that is in thermodynamic equilibrium with the
surrounding air at a given temperature and relative humidity.
3.1.7 equilibrium relative humidity, ERH—the relative humidity of the air in a sealed chamber that is in thermodynamic
equilibrium with a sample of material in that chamber.
3.1.8 humidity ratio, W, n—the ratio of the mass of water vapor to the mass of dry air contained in a sample of moist air.
3.1.9 moisture content, MC, n—the ratio of the mass of water in a material to the oven-dry mass of the sample expressed as a
decimal fraction or percentage.
3.1.9.1 Discussion—
Oven-dry refers to the removal by heating of all adsomcrbed and free water in the interstitial pores of the material. Crystalline
water such as contained in gypsum molecules is not included.
3.1.10 relative humidity, ϕ, n—the ratio of the amount of water vapor in air to the amount of water vapor in saturated air at the
same temperature and pressure.
3.1.10.1 Discussion—
Equivalent to the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure at the same temperature and
pressure.
3.1.11 test uncertainty ratio, TUR, n—comparison between the accuracy of the Unit Under Test (UUT) and the estimated
calibration uncertainty stated with a confidence level of 95 % (K=2).
3.1.12 water activity, A , n—the ratio of the water vapor pressure in a material to the vapor pressure of pure water at the same
w
temperature.
3.1.12.1 Discussion—
Water activity is an intrinsic property derived from fundamental principles of thermodynamics and physical chemistry. It is a
measure of the energy status of the water in a system. Commonly used for food preservation analyses, it can be interpreted here
as the amount of water in a porous material that is available to impact the performance characteristics of the material or to support
mold growth.
C1789 − 14 (2018)
4. Summary of Test Method
4.1 These test methods provide a method for calibrating the scale on conductance and dielectric meters for various types of
gypsum boards and panels for use in field measurement of moisture content during storage, construction and use in building
assemblies.
4.2 The calibration is based on the MC of the test specimen. The corresponding ERH is determined by use of a calibrated direct
read relative humidity meter.
4.3 ERH is essentially equivalent to water activity Aw which is a measure of the amount of moisture in a material that is
available to impact the performance characteristics of that material.
4.4 Due to the various core and/or facing additives that are used to modify the moisture absorption characteristics, strength
and/or other properties for specific applications, a separate calibration is required for each type of gypsum board or panel to be
measured.
4.5 The test method has the following steps:
4.5.1 Measure the dry weights of the test specimens.
4.5.2 Determine the time step for the drying intervals that will provide sufficient data points to develop a calibration curve.
4.5.3 Saturate the samples with water.
4.5.4 Dry the samples in steps, recording after each interval the moisture content by weight of each sample and the temperature,
relative humidity (ERH), and absolute humidity of the atmosphere in moisture equilibrium with each sample.
5. Significance and Use
5.1 This Standard Test Method is intended for use in calibrating hand-held meters to accurately read from approximately 30 to
90%90 % ERH. Moisture content is related to the ERH or water activity of a material.
5.2 Hand-held meters provide a rapid means of sampling the moisture content of gypsum boards and panels during manufacture
and for field inspection during and after building construction. However, these measurements are inferential, that is, electrical
parameters are measured and compared against a calibration curve to obtain an indirect measure of moisture content. The electrical
measurements are influenced by the actual moisture content, a number of other gypsum board and panel variables, environmental
conditions, the geometry of the measuring probe, and the design of the meter. The maximum accuracy can only be obtained by
an awareness of the effect of each parameter on the meter output and correction of readings as specified by these test methods.
5.3 Electrical conductance and dielectric meters are not necessarily equivalent in their readings under the same conditions.
When this test method is referenced, the type of meter that is being used must be reported with the relevant ranges for precision
and bias as specified in this standard.
5.4 Both types of meters are to be calibrated with respect to ERH as described in this standard.
6. Apparatus
6.1 Laboratory equipment for moisture content determination by direct method:
6.1.1 Forced Air Oven—Vented electric furnace capable of maintaining a steady-state temperature of 45 6 3°C (113 6 5°F).
6.1.2 Environmental Chamber—Chamber capable of maintaining a controlled temperature of 20 6 2ºC (68 6 4ºF) and relative
humidity within the range 30 to 90 % 6 5 %.
6.1.3 Electronic Balance or Scale—Electronic scale capable of weighing each test specimen to within 60.10 g (60.0035
oz).(60.0035 oz).
6.1.4 Relative Humidity Test Meter—The meter shall be capable of reading between 30 and 90 % relative humidity. The
calibrated test uncertainty ratio (TUR) of this meter shall not be less than 4:1 over the range of measure cited.
6.1.4.1 Meter shall have removable temperature/humidity probes that can be sealed into sealed plastic bags.
6.1.5 Humidity Box—Insulated box made of materials impervious to water vapor such as plastic or sheet metal, sealed with a
gasketed lid. Open trays of clean, distilled water are positioned in the box so as to keep the atmosphere within the box saturated
with water vapor. Open mesh shelving or racks are used to support samples above the water.
6.1.6 Zip Sealed Plastic Bags—Commercially available plastic freezer weight plastic food storage bag with a zipper type closure
that seals and prevents water vapor transmission.
6.1.7 Psychrometric Chart—Graphical presentation of the thermodynamic properties of moist air.
7. Laboratory Calibration
7.1 This procedure is designed for full-scale calibration of the meter. A minimum of 45 calibration specimens shall be fabricated
with a target of ten (10) calibration steps ranging from ERH of 30 to 90 %.
NOTE 1—30%30 % relative humidity represents a practical lower limit on moisture content found in buildings and the accuracy of readings above
90%90 % relative humidity is problematic. The calibration should not be extrapolated below the lowest value tested or above the highest value tested.
Material of the type to be calibrated shall be prepared and tested in a manner that is consistent with the following calibration procedures.
7.2 Specimens shall be free of visible irregularities.
C1789 − 14 (2018)
7.3 Select a minimum of 45 specimens, each measuring 100 mm 100 mm wide by 200 mm long (4 in. by 8 in.), for each given
sample of board or panel.
7.3.1 The specimens shall be divided into a minimum of three (3) groups of 15 specimens each.
7.3.2 Each specimen shall be assigned a group designation and a specimen number (for example.,example, A-1, A-2, A-3, B-1,
B-2, B-3, etc.) and and so forth) and labeled with a pencil or waterproof ink.
8. Determine Dry Specimen Weights and Equilibrium Humidity Ratios
8.1 Determine the dry weight of each specimen.
8.1.1 Place the test specimens into forced air oven set at 45 °C (113 °F). 45°C (113°F). Arrange the specimens so that heated
air circulates freely around all sides of the specimens. Use racks or holders to keep the specimens separated sufficiently to allow
air flow between the specimens.
8.1.2 Remove and weigh each test specimen at one hour intervals.
8.1.3 The test specimen is deemed to be dry when three consecutive weighings show no change in weight within 60.10 percent
60.10 % of the dried sample weight.
8.1.4 Record the dry weight of each specimen.
8.2 Determine the humidity ratio of the trapped environment that is in moisture equilibrium with each specimen.
NOTE 2—Humidity ratio is used as the temperature is likely to vary during the course of the test and relative humidity will vary with temperature at
constant moisture content. Humidity ratio and dew-point temperature do not vary with temperature at constant moisture content and can be calculated
from the temperature and relative humidity values measured by direct read instruments.
8.2.1 Place the specimen in a zip sealed plastic bag to contain it in a trapped atmosphere.
8.2.2 Insert a temperature/relative humidity probe through the wall of the bag and seal tightly.
NOTE 3
...