How do I Use Rigid Millboard Insulation?

Millboard is an insulation material made of fibers tightly compressed between paper or other covering.

It is used in walls and ceilings, especially around furnaces, fireplaces or other places subject to high temperatures. In industrial applications, it is used in metal molding, foundries and kilns, glass manufacturing and other situations where resistance to heat is imperative. Once most millboard was made of asbestos fibers, but in 1977 the United States banned asbestos in most construction because of health dangers. Inhaled asbestos fibers can cause serious and usually fatal diseases, including cancers. Now most millboard in America is made of ceramic, clay or cement fibers.

Use millboard any place which will be subject to extreme heat. Most of it is capable of withstanding temperatures of 2,000 degrees Fahrenheit or more. It can block heat, withstand heat of substances such as molten metal, and can seal off extremely hot areas. It is easy to cut, punch with a die cutter or even mold into shapes --- although it is used around furnaces and fireplaces in its rigid form.

Choose a millboard specifically for your project. Some is made with kaolin, a silica material, or similar form of clay. Some types use a form of cellulose, others ceramic materials. Some are composed of cement fibers. The temperature rating will vary with the fiber content and some millboards use a combination of fiber types. The composition also will affect the ease of cutting and installation. Asbestos millboard is still made and used in some parts of the world and has some special industrial applications in America.

Cut your millboard with a saw, although many special situations use a die-cut, in which a shape is stamped out of the millboard; this would be done to line a rotary kiln or industrial boiler or to make gaskets. If you are using a cement-based millboard for exterior wall cladding, you will install it much like wood siding. You can use drywall screws in interior walls or ceilings.

Things You Will Need

  • Saw or other cutter

About the Author

Bob Haring has been a news writer and editor for more than 50 years, mostly with the Associated Press and then as executive editor of the Tulsa, Okla. "World." Since retiring he has written freelance stories and a weekly computer security column. Haring holds a Bachelor of Journalism from the University of Missouri.