Understanding Materials – Gypsum Board

Introduction –

Today we are going to begin our series about construction materials and their applications in buildings.  There are a vast number of materials that any single construction project will use, and we will examine the most widely used materials.  The information in each of these posts are just the main highlights and your architect and design professionals will need a much deeper knowledge of each material discussed to best understand where in your project that material should or shouldn’t be used.  If you have a question about specific material not discussed or have more in depth questions regarding he materials explained contact us at info@gdsatx.com for one of our professionals to assist you.

Gypsum Board –

Gypsum Board (also known as plasterboard, wallboard or drywall) is a panel made of gypsum plaster pressed between two thick sheets of paper. It is typically used to make interior walls and ceilings. Gypsum Board (Gyp. bd.) construction became a popular alternative to traditional lath and plaster because of speed and efficiency of installation[1].

Gyp. bd. panels are usually manufactured in 48” wide sheets that vary in length based on the need of the project. Typical panel thicknesses are 12” and 58”, with panels also available in other various thicknesses such as 14” and 38”. Both 12” and 58” panels can come in “Type X” (with additives to increase the natural fire resistance), and are used where an increased fire-resistance rating is required. Of the most common sizes, 58” panels are the standard in construction [2]. Gyp. bd. can act as the finished layer of an assembly or as the substrate for another finish material. The finish material can be applied directly to the gyp. bd. or can be installed over the panels, and can vary from paint to tiles to wall panels.

A drawback to gyp. bd. is that it is easily damaged by exposure to water. Gyp. bd. is a porous substance that supports the growth of mold when installed incorrectly and in an environment conducive to mold growth. Moisture will cause gyp. bd. to swell and eventually break down, requiring replacement [3]. However, there are various types of “special” gyp. bd., as well as construction practices, that can be utilized in order to combat the risk of exposure to moisture.

There are numerous different types of gyp. bd. Each type has a different application to ensure that the construction of the assembly is done correctly and is code compliant. These types include regular white board (gyp. bd.), fire-resistant (“Type X”), greenboard (contains an oil-based additive in the green colored paper covering that provides moisture resistance), cement board (a composite of cement and reinforcing fibers [4]), soundboard/sound engineered drywall (made from wood fibers to increase the sound rating-STC), lead-lined gyp. bd. (used around radiological equipment), and impact resistant gyp. bd.  There are other types of gyp. bd. for other more specific situations, however, these will be the most common types in a general application in a wide range of construction projects.

“Type X” –

When used as a component in fire barriers, gyp. bd. is a fire protection item. When exposed to heat or fire, this water in the gypsum boils away limiting the heat transfer from room to room. Therefore, a fire in one room will be contained from an adjacent room by a fire-resistance rated gyp. bd. assembly and will not cause damage to the adjacent room until the water in the gypsum is gone, expressed as a function of time (i.e. 1-hr fire rated assembly). Generally, increasing the number of layers of “Type X” gyp. bd. in a fire rated assembly, increases the fire-resistance rating of the assembly [5]. “Type X” would be used in places where the building code and ordinances require a specific fire rating. 

Greenboard –

Greenboard is water resistant, but not waterproof. It is to be used when the construction assembly occurs in damp environments that are subject to high levels of humidity and infrequent exposure to water. However, greenboard should not be used in wet locations because it is still subject to mold growth and deterioration due to exposure to water [4]. Green board would be installed in areas with hand sinks, food prep areas, areas with instrument sinks, and some restroom applications.

Cement Board

When an environment is continually exposed to water spray cement board is used. Cement Board is a combination of cement and reinforcing fibers formed into sheets. Typically, these sheets are ¼” to ½” thick. As a tile backing board, cement board has better long-term performance than paper-faced gypsum core products because it will not mold, mildew, or physically break down in the continued presence of moisture or leaks. Cement board is not actually waterproof, but it is highly resistant to absorbing moisture and has excellent drying properties [6]. The main drawbacks to cement board are the added weight to material itself (over twice as heavy as regular gyp. bd.), cutting cement board requires carbide-tipped saw blades, and the cost. Cement board would be used in areas such as showers, and wall backing for bathing tubs.

Soundboard/Sound Engineered Drywall (SED)

Sound vibrations can travel through elastic mediums, which include gyp. bd.  Therefore, vibrations can travel through gyp. bd. and special acoustical precautions need to be addressed if sound control is an important issue.

SED is a sounds deadening gyp bd. that absorbs the sound as to not let as much noise transfer from room to room. Sound travels through walls by vibration through the materials. SED is designed to reduce the vibrations by absorbing as opposed to conducting the sound waves [7]. It can be used either as the finished layer or as additional layer of gyp. bd. SED would be used anyplace noise transfer would be a major concern.

Lead Lined Gyp. Bd.

Lead lined gyp. bd. is a specialty type of gyp. bd. supplied with lead lining bonded to the drywall. It is used in very specific situations where radiation is a concern.  In addition, most jurisdictions will require a physicists report of the areas in question and to ensure that the shielding requirements are adequate.  The most common use for lead lining, but not limited to, is to protect adjacent rooms and areas from the radiation emitted in radiology rooms and x-ray machines.

Impact Resistant Gyp. Bd.

In areas where there is heavy traffic and risk for damage to walls, impact resistant gyp. bd. should be installed. Impact resistant gyp. bd. is a version of gyp. bd. that has heavy natural-finish paper on the face, and strong liner paper on the back. The face paper is folded around the long edges to reinforce and protect the core [8]. Impact resistant gyp. bd. should be installed in order to minimize the damage done to the wall where equipment and furnishings are located and can create dents and cracks in walls. Also, areas and rooms where other materials require extra strength for installation should utilize the added strength of impact resistant gyp. bd.

Overall, gyp. bd. will be the most visible material on a construction project. It is imperative to understand the different types of gyp. bd. that are available for each application, how the gyp. bd. affects finish selections for each assembly, and strengths and weakness of the material. Thought, preparation, and consideration will have to be incorporated into every aspect of the design, even with the most basic industry standard – gyp. bd. assemblies.

References

1.     Preservation Brief 21: Repairing Historic Flat Plaster-Walls and Ceilings (http://www.nps.gov/history/hps/TPS/briefs/brief21.htm#Historical%20Background)
2.     Gypsum Association – Fire Resistance Design Manual (GA-600-2009) (http://www.gypsum.org/pdf/GA-600-09_Print_7_Megs.pdf)
3.     http://www.cmhc-schl.gc.ca/en/co/maho/yohoyohe/momo/momo_007.cfm
4.    http://homerenovations.about.com/od/wallsandtrim/a/artgreenboard.htm
5.     http://www.nationalgypsum.com/resources/fire-safety.htm
6.     http://www.usg.com/durock-cement-board.html
7.     http://www.supressproducts.com/soundproofing-articles/Sound-Engineered-Drywall.html
8.     http://www.usg.com/sheetrock-abuse-resistant-gypsum-panels.html

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