What is Type X Gybsum Board?

1 what is Type X GYPSUM board ? A Firm Understanding of Type X Gypsum board is a Must as Emphasis on Fire Resistance Efficiency Continues to Grow (NOTE: A frequent question asked of the Gypsum Associa- tion of fire resistant gypsum products. In an effort to assure tion is some variation of the following: what is the dif- that the question is answered thoroughly and well, the Gyp- ference between regular and type X gypsum board , and why sum Association has prepared the following article. It and when should I use the latter? This kind of question discusses how and why type X board was developed and is also asked of the contractor, and how it is answered can what this special product means to the gypsum industry.). make the difference between proper or improper applica- I ncreasing fire resistance efficiency has been the prime concern of gyp- sum manufacturers as this industry has By Don MacQueen Technical Director fire-resistance in assemblies similar to the fire-resistance of gypsum or metal lath and plaster which, for years, was The Gypsum Association grown over the past five decades.

2 Con- considered as the only acceptable one- siderable developmental effort has hour fire-resistive construction. gone into maximizing the inherent fire The primary reason for the success resistant qualities of gypsum board face exposed to the heat, back through of metal lath and gypsum plaster products. A main result of this effort the mass. As the water is driven out, assemblies as a fire proofing, was the has been the introduction of type X the material remains noncombustible ability of the metal lath to reinforce the gypsum board . and offers good insulation to heat calcined material, holding it in place Even in the early years of the in- transfer. But, as the calcination pro- for a long period of time. This rein- dustry, it was apparent that gypsum, ceeds through the gypsum product, forcement prevented cracks from by itself, or in combination with an ag- shrinkage occurs and cracks develop becoming large enough to allow gregate, was a barrier to the passage because of the substantial loss of passage of heat, smoke and flame.

3 In of heat, fire and smoke for long volume. These cracks ultimately per- the late 1930's and early 1940's it was periods of time. This was due to the mit the passage of fire and heat directly the aim of industry chemists to incor- chemical makeup of the material and through the mass. If the material is in porate similar characteristics in gypsum its reaction under heat. Gypsum, (or a ceiling installation, this would allow board that might accomplish the same as it is technically known, dehydrous the material to drop. But with the results at less cost. calcium sulphate ), is about 50% development of type X gypsum board , This research led to experiments in water by volume and about 20% water this problem was greatly reduced. adding various noncombustible fibers by weight. When subjected to heat, The major factor contributing to the to the gypsum core, including wood gypsum board goes through a process rapid increase in the use of gypsum fibers, mineral wool, glass wool, and called calcination during which some board interiors in recent decades has fiberglass strands.

4 Unexpanded ver- of the water separates from the been the development of a product miculite particles, well distributed in calcium sulphate, changes into steam, with a core having greater fire- the core, expand when heat is applied, and is driven from the material. This resistance than conventional gypsum counter-balancing the shrinkage of the requires heat at the surface and pro- board . In simple comparison, a 5/8" gypsum which occurs as it loses its gressive action working from the sur- thick extra fire-resistant board gives water. This provides a core more ther- Construction Dimensions/May 1984 19. After a significant number of gypsum manufacturers had the extra fire-resistive board on the market , with proven performance in several standard assemblies, the Gypsum Association began to push for industry standards that would be acceptable to building code officials, testing organizations, and the manufacturers. This was essentially accomplished in 1955 .. for type X.. mally stable under exposure to fire.

5 Glass fibers, well dispersed throughout the core, serve as a reinforcing material holding the board core together. The patent issued October 17, 1950. to Michael Croce of Bestwall was based on material filed originally in 1943. Fire tests on full scale wall panels at Underwriters' Laboratories resulted in the first listing of special fire- resistant gypsum board in 1946. This was originally listed as Design #1-45. minutes, and currently is shown by UL. as Design Number U 317. Further lab- oratory work improved the product, resulting in a board which, when used as the ceiling of a floor/ceiling assembly, gave fire protection equal to the standard lath and plaster assembly. Experimentation involved addition to the core of various materials which expanded when exposed to heat. It was found that vermiculite of the proper Many hours of research and development are invested .. grade appeared to be most suitable. The purpose of the vermiculite was to compensate for shrinkage in the core under heat.

6 Fire tests of a floor/ceil- ing assembly with board , incor- porating the unexpanded vermiculite and the noncombustible fibers, devel- oped a 45 minute fire-resistance rating equal to that developed in the wall. A Major Advance .. This was a major step forward. Un- til this time, a partition surfaced on both sides with " regular gypsum board could provide up to 40 minutes fire-resistance with a wood joist and floor assembly with " regular gyp- sum board as the ceiling, only 25. minutes. A wood floor-and-ceiling assembly with no fire protection, tested by the National Bureau of Standards .. before a product such as type X gypsum board reaches the market . (NBS), withheld the passage of fire and 20 Construction Dimensions/May 1984. heat and sustained the required load wood framing members, when tested cepted and approved under the Uni- for 15 minutes. With " regular in accordance with the requirements of form Building Code in 1951 (first board added as a ceiling protection to methods E 119.)

7 Research Report No. 296, September, this assembly, the fire-resistance in- The gypsum industry was not en- 1951). By 1955, there was acceptance creased to 25 minutes-an additional tirely convinced of the usefulness of by over 250 major cities throughout ten minutes of fire endurance. The " the type X product when it was first the United States. As the importance extra fire-resistant board developed by introduced. Some gypsum manufac- of the type X product developed, other Bestwall produced 45 minutes of fire turers wanted to do their own ex- gypsum manufacturers began to mar- resistance, or added 30 minutes of pro- perimenting and testing and did not, ket competitive materials. However, in tection to the assembly, or three times at that time, take advantage of in- view of the acceptance of Bestwall's the protection offered by the " novative development work done by Firestop, these manufacturers found regular gypsum board . the Certain-teed Products Corporation it advisable to have their products also The Bestwall chemists continued to in the early 1940's.

8 However, architects officially fire tested at Underwriters'. improve the core formulation to in- welcomed the type X product as it Laboratories. Through the early years, crease the performance of the board . enabled them to meet the one-hour other test facilities included Ohio This led to additional patents being fire-resistance requirements with a State University, University of Cali- granted to Michael Croce and Clarence wider choice of assemblies. The fornia (Berkeley), and the Fire Preven- G. Shuttleworth in June of 1954. The manufacture of type X board under tion Research Center (Gardena, patent was based on original applica- the UL reexamination service, was ac- California). tions made in July of 1951 and repre- sented the primary development incor- porating glass fibers in gypsum. It had been found from experiments that while several other fibers could per- form satisfactorily to attain fire resistance products, all but one resulted in some sort of difficulty. Many types of glass fibers were checked before the chemists found a satisfactory one.

9 The most successful consisted of drawn, textile glass fibers formed into strands with a water- soluable binder. The binder was strong enough to hold the fibers together in the glass fiber manufacturing process during which the filaments were gathered into strands and rovings. When the strands were cut into short pieces and agitated in a wet plaster slurry the binder softened and permit- ted the individual filaments to separate and disperse rapidly throughout the mix. At about the same time, Commit- tee C-11 on Gypsum of the American Society for Testing and Materials (ASTM) finalized a standard definition for this new extra fire-resistant gypsum wallboard. The ASTM Standard, C. 36, includes the definition of a product designated as type X gypsum wall- board . It reads: Type X (Special Fire- Retardant) designates gypsum wall- board complying with this specification that provides at least one-hour fire retardant rating for boards 5/8" (16 mm). thick, or -hour fire retardant rating for boards " (13 mm) thick, applied to a partition in single-layer nail ap- plication on each face of load-bearing Construction Dimensions/May 1984 21.

10 In 1956, the Bestwall Gypsum Com- pany was formed to take over the gyp- sum operations of Certain-teed. Bestwall continued to test additional assemblies with their 5/8" type X prod- uct. These tests proved 2- and 3-hour fire resistive partition assemblies. Later, up to 2-hour fire-resistive floor and ceiling assemblies with single layer applications, 2- and 3-hour column fire proofing, and other assemblies with metal framing, were tested successfully. After a significant number of gyp- sum manufacturers had the extra fire- resistive board on the market , with proven performance in several stan- dard assemblies, the Gypsum Associa- tion began to push for industry stan- dards that would be acceptable to building code officials, testing organizations, and the manufacturers. This was essentially accomplished in 1955 with the addition of the defini- tion for type X to the ASTM Standard C 36 on Gypsum board . This was a major development in the history of this remarkable building material.