By Peter V. Burns, NWCB Director of Technical Services
An ongoing challenge for gypsum wallboard (GWB) installing and finishing contractors are the ever-changing interior environmental conditions they work in. The concern stems from the experience and knowledge of the potential for performance issues such as the appearance of joint ridging, screw depressions a.k.a. delayed shrinkage, starved joints and joint cracking that are symptoms of interior environmental jobsite conditions not being compliance with the provisions of ASTM C840, the Gypsum Association, the IBC or manufacturers recommendations.
One of history’s great scientist, William Thompson known as Lord Kelvin after being Knighted by the Queen of England for his formulation of the absolute temperature scale or the 'Kelvin' scale and his contributions to the 1st and 2nd Laws of Thermodynamics, stated his belief on the importance of measurements:
“When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science " [1]
By developing and implementing a formal procedure for informing the project team of your environmental condition requirements at a pre -construction meeting and discussing how you will be measuring and documenting jobsite interior ambient temperature, relative humidity, and dewpoint temperatures, contractors will have the confidence, knowledge and documentation that the environmental parameters during construction and finishing met industry standards.
The NWCB recognizes the following industry standards and guidance documents, along with manufacturers installation instructions and guidance documents for installing, finishing, judging, and repairing gypsum board assemblies:
Industry Standards and Guidance Documents
ASTM C840 Standard Specification for Application and Finishing of Gypsum Board Gypsum Association
GA-216 Application and Finishing of Gypsum Panel Products
Gypsum Association GA-214 Levels of Finish for Gypsum Board Panels
Gypsum Association GA-236-2017 Joint Treatment Under Extreme Weather Conditions
Gypsum Association GA- 221 Repair of Joint Ridging
Gypsum Association GA -222 Repairing Screw or Nail Pops
United States Gypsum (USG)- Evaluating Jobsite Environmental Conditions
ICC IBC- Chapter 25 Gypsum Board, Gypsum Panel Products and Plaster
ASTM C840- Standard Specification for Application and Finishing of Gypsum Board
4. Environmental Conditions
“When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science " [1]
By developing and implementing a formal procedure for informing the project team of your environmental condition requirements at a pre -construction meeting and discussing how you will be measuring and documenting jobsite interior ambient temperature, relative humidity, and dewpoint temperatures, contractors will have the confidence, knowledge and documentation that the environmental parameters during construction and finishing met industry standards.
The NWCB recognizes the following industry standards and guidance documents, along with manufacturers installation instructions and guidance documents for installing, finishing, judging, and repairing gypsum board assemblies:
Industry Standards and Guidance Documents
ASTM C840 Standard Specification for Application and Finishing of Gypsum Board Gypsum Association
GA-216 Application and Finishing of Gypsum Panel Products
Gypsum Association GA-214 Levels of Finish for Gypsum Board Panels
Gypsum Association GA-236-2017 Joint Treatment Under Extreme Weather Conditions
Gypsum Association GA- 221 Repair of Joint Ridging
Gypsum Association GA -222 Repairing Screw or Nail Pops
United States Gypsum (USG)- Evaluating Jobsite Environmental Conditions
ICC IBC- Chapter 25 Gypsum Board, Gypsum Panel Products and Plaster
ASTM C840- Standard Specification for Application and Finishing of Gypsum Board
4. Environmental Conditions
- Application of Gypsum Board, Joint Treatment Materials, and Adhesives--Room temperature shall be maintained at not less than 40°F (4°C) during application of gypsum board except when adhesive is used for the attachment of gypsum board. For the bonding of adhesive, joint treatment, texturing, and decoration, the room temperature shall be maintained at not less than 50°F (10°C) for 48 h prior to application and continuously thereafter until completely dry. See X7.7 for additional detail regarding environmental control during the installation and finishing process.
- When a temporary heat source is used, the temperature shall not exceed 95°F (35°C) in any given room or area.
- Adequate ventilation shall be maintained in the working area during installation and curing period.
GA-214- Levels of Finish for Gypsum Board Panels
Environmental Control
The potential for finishing and decorating problems are minimized when temperature, humidity, and airflow remain constant and as close to occupancy environmental conditions as possible. A minimum temperature of 50°F (10°C) shall be maintained continuously for 48 hours prior to and throughout the finishing process until the project is completed/occupied.
United States Gypsum Corp. (USG)- Evaluating Jobsite Environmental Conditions
The ideal conditions for the installation, finishing and decorating of GWB are those that closely match the intended occupancy environment. This level of temperature, humidity, ventilation, and free moisture should be maintained continuously before stocking, during installation and after the completion of the finishing and decorating processes. Sharp swings in temperature, ventilation, and/or humidity, like those that occur when environmental control systems are turned off at night or on weekends, should be avoided.
Rapid changes in environmental conditions cause thermal and hygrometric movement which is likely to cause cracking, bond loss or other problems.
Manufacturers’ specific recommendations should always be followed, so contractors should be aware of and follow those recommendations. If a temporary heat source is used, the temperature should not exceed 95°F in any room or area. Adequate ventilation must be supplied to ensure that drying conditions are met and maintained. Contractors need to be aware that some temporary heat sources do not have provisions for venting combustion products to the outside of the building or workspace and can significantly increase humidity in the work area.
Environmental Control
The potential for finishing and decorating problems are minimized when temperature, humidity, and airflow remain constant and as close to occupancy environmental conditions as possible. A minimum temperature of 50°F (10°C) shall be maintained continuously for 48 hours prior to and throughout the finishing process until the project is completed/occupied.
United States Gypsum Corp. (USG)- Evaluating Jobsite Environmental Conditions
The ideal conditions for the installation, finishing and decorating of GWB are those that closely match the intended occupancy environment. This level of temperature, humidity, ventilation, and free moisture should be maintained continuously before stocking, during installation and after the completion of the finishing and decorating processes. Sharp swings in temperature, ventilation, and/or humidity, like those that occur when environmental control systems are turned off at night or on weekends, should be avoided.
Rapid changes in environmental conditions cause thermal and hygrometric movement which is likely to cause cracking, bond loss or other problems.
- Thermal movement is created by expansion and contraction of construction materials due to changes in temperature.
- Hygrometric movement occurs due to the absorption or evaporation of water into or out of construction materials.
Manufacturers’ specific recommendations should always be followed, so contractors should be aware of and follow those recommendations. If a temporary heat source is used, the temperature should not exceed 95°F in any room or area. Adequate ventilation must be supplied to ensure that drying conditions are met and maintained. Contractors need to be aware that some temporary heat sources do not have provisions for venting combustion products to the outside of the building or workspace and can significantly increase humidity in the work area.
Un-vented space heater
GA-216-20016
4.3.4.2 When portable gas or kerosene heaters are used, the extra humidity that they produce shall be removed.
4.3.4.3 Adequate and continuous ventilation shall be provided in the working area during the installation and the drying or setting period.
Relative Humidity
Relative humidity (RH) is the amount of water vapor in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature. There are no references or requirements for a specific interior jobsite RH for the finishing trades in any of the guidance documents or standards. RH along with temperature, is however a key metric that affects drying time of joint compounds. The chart below illustrates the important relationship between RH, temperature and drying time. For projects to remain on schedule, crews need to know what the interior conditions are by taking measurements and adjusting as needed.
4.3.4.2 When portable gas or kerosene heaters are used, the extra humidity that they produce shall be removed.
4.3.4.3 Adequate and continuous ventilation shall be provided in the working area during the installation and the drying or setting period.
Relative Humidity
Relative humidity (RH) is the amount of water vapor in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature. There are no references or requirements for a specific interior jobsite RH for the finishing trades in any of the guidance documents or standards. RH along with temperature, is however a key metric that affects drying time of joint compounds. The chart below illustrates the important relationship between RH, temperature and drying time. For projects to remain on schedule, crews need to know what the interior conditions are by taking measurements and adjusting as needed.
USG recommends:
“Temperature, humidity and airflow should remain constant and as close to occupancy conditions as possible. The potential for finishing and decorating problems is minimal when job environmental conditions match occupancy environmental conditions. Controlling and maintaining environmental conditions is key. Changes and/or fluctuations in temperature, humidity and airflow can have a profound adverse effect on finishing. Temperatures within the building should be maintained within the range of 55°F to 70°F. Adequate ventilation should be provided.”[2]
The hygroscopic nature of drywall and the understanding that it is “very quick to absorb moisture but very slow to dry out” [3] leads to the recommendation that contractors need to be in control of indoor environmental conditions and avoid large and rapid changes or fluctuations in temperature and humidity. Failure to follow these recommendations can lead to joint bond failure, delayed shrinkage, ridging, nail pops, joint flashing, and board sagging.
Thermo-hygrometers measure both ambient air temperature and relative humidity, some will even calculate and display dew point temperatures. We have found products ranging from $10-$25 dollars that will record high and readings over a 24-hour period or data loggers that will record for months.
“Temperature, humidity and airflow should remain constant and as close to occupancy conditions as possible. The potential for finishing and decorating problems is minimal when job environmental conditions match occupancy environmental conditions. Controlling and maintaining environmental conditions is key. Changes and/or fluctuations in temperature, humidity and airflow can have a profound adverse effect on finishing. Temperatures within the building should be maintained within the range of 55°F to 70°F. Adequate ventilation should be provided.”[2]
The hygroscopic nature of drywall and the understanding that it is “very quick to absorb moisture but very slow to dry out” [3] leads to the recommendation that contractors need to be in control of indoor environmental conditions and avoid large and rapid changes or fluctuations in temperature and humidity. Failure to follow these recommendations can lead to joint bond failure, delayed shrinkage, ridging, nail pops, joint flashing, and board sagging.
Thermo-hygrometers measure both ambient air temperature and relative humidity, some will even calculate and display dew point temperatures. We have found products ranging from $10-$25 dollars that will record high and readings over a 24-hour period or data loggers that will record for months.
 24-hour high/low thermo-hygrometer |  Data-logging thermo-hygrometer |
By deploying data logging thermo-hygrometers throughout the interior space of a project, you will have a record of hourly temperatures, relative humidity, and dewpoint temperatures for the duration of a project. Data can be downloaded to smart phones via Bluetooth on a daily or weekly basis. These tools never miss a reading and will catch data overnight and from weekends that might otherwise be missed. Below is an example of logger data pinpointing the time that temporary heat was added to the interior space.
Condensation on GWB that has a surface temperature below the dewpoint
Dewpoint
Dewpoint is the temperature at which moisture will begin to condense out of the air. Think of the classic example of a glass of lemonade on a hot humid day. When moisture laden air meets the cool surface of an ice filled glass, condensation will form on the glass because the air has hit its dewpoint. This same phenomenon can occur on construction sites. USG has taken the position that “no compounds or coatings should be applied unless the surface temperature is at least 5°F above the dew point temperature of the room air and any ventilation air flowing over the surface.”
You will need to measure the interior ambient air temperature and relative humidity along with the surface temperature of the wall. You will also need an Infra-Red spot thermometer to measure the wall temperature.
Dewpoint is the temperature at which moisture will begin to condense out of the air. Think of the classic example of a glass of lemonade on a hot humid day. When moisture laden air meets the cool surface of an ice filled glass, condensation will form on the glass because the air has hit its dewpoint. This same phenomenon can occur on construction sites. USG has taken the position that “no compounds or coatings should be applied unless the surface temperature is at least 5°F above the dew point temperature of the room air and any ventilation air flowing over the surface.”
You will need to measure the interior ambient air temperature and relative humidity along with the surface temperature of the wall. You will also need an Infra-Red spot thermometer to measure the wall temperature.
 |  |
- Interior air temp. measured at 50°F
- Interior RH measured at 80%
- Gypsum board surface measured 42°F
Using the chart below or you can find the dew point for a given temperature and relative humidity.
Example: Temperature of 50°F and relative humidity of 80% results in a dew point of 44°F.
No compounds or coatings should be applied in this case unless the surface temperature is at least 49°F. [4]
At a minimum of 48 hours prior to the beginning of the finishing process, GWB finishing contractors need to begin to measure, monitor and record interior environmental conditions in order to ensure that environmental conditions they are given to work in meet industry standards. Doing so sends a powerful message of the importance to the end results of the project that these conditions mean.
- Lord Kelvin, Popular Lectures and Addresses, Volume 1,” 1891. 1883-05-03, "Electrical Units of Measurement",”
- The USG Gypsum Construction Handbook Sixth Edition, 2009, p.174
- Moisture parameters and fungal communities associated with gypsum drywall in buildings, Sandra Dedesko and Jeffrey A. Siegel, Microbiome 2015
- Evaluating Jobsite Environmental Conditions, United States Gypsum Company 2012
RSS Feed
