January 9, 2008
Article misleading on MgO fire-resistanceEditor:
While the November 2007 article, “MgO Board: A Primer on the Next Generation of Sheathing,” was quite interesting, it became less appealing when the author used open-ended comparative statements such as “much-improved characteristics” without substantiation. This was particularly the case when he referred to the “fire-resistance” abilities of MgO board as compared to gypsum board.
Conventional building codes do not require an analysis of the fire-resistive characteristics of individual building materials when those materials are used in a wall or ceiling system. While individual materials may be evaluated for specific characteristics such as flame-spread, systems are compared through the use of an ASTM E 119 test.
Given that gypsum board almost always has to be installed to framing members–it can’t magically float in the air–it is tested for fire-resistance as a part of a system. The same would be the case for an MgO board or panel product when it is installed as a part of a wall or ceiling system.
As a consequence, saying that one material is “more fire-resistant” than another when both of the materials are required to be installed as a part of a system to function properly distorts the real meaning of a fire-resistance rating. No manner exists, other than possibly extrapolating some conclusion from a series of E 119 tests, to establish the claim.
In addition, all systems that achieve the same, specific hourly fire-rating–whether they are constructed primarily from gypsum, masonry, or MgO board–are viewed as having equivalent fire resistance by model building codes. It doesn’t matter how thick or thin the systems are, or what the characteristics of the individual materials in the system are; what matters, in the end, is the assigned fire rating. If two dissimilar systems achieve the same hourly fire rating, neither is more fire-resistant than the other.
Few materials have as strong a record as a fire-resistant material as does gypsum board. Making an unsubstantiated comparative remark as was done in the article was inappropriate.
Michael A. Gardner
Your article on MgO board presents claims about the product that I believe warrant further examination. The author’s assertions that MgO represents a “much-improved” alternative to gypsum wallboard or cement board, and that it is “green/eco-friendly” are difficult to believe when one looks closely at the actual product information and technical data.
Taking the latter claim first, manufacturers actively involved in “green” manufacturing and building practices are aware that the USGBC’s LEED certification system is based not only on using recycled content in the product, but on reducing transportation-related energy consumption by sourcing building materials as close to the project site as possible. This aspect of being “green” is impossible in the case of MgO. As the author states, most production of MgO board takes place near the site of large deposits of magnesium oxide – primarily China and the Mideast. Thus, using the board for projects here in the U.S. entails transporting it across great distances via the world container shipping fleet, which itself has come under scrutiny recently for its contribution to air pollution.
By contrast, domestically-produced gypsum wallboard is often produced and shipped close to the end user. In addition, all of the face and back paper on gypsum wallboard is made from 100 percent recycled paper. Currently, approximately 25 percent of all domestically-produced gypsum wallboard is manufactured from synthetic gypsum, a by-product collected from the smokestack scrubbers of power plants located close to the wallboard plant that would otherwise go to a landfill.
Readers should more closely examine the claim that MgO is “sort of like drywall or cement board – but with much-improved characteristics, such as fire resistance, weatherability, strength, resistance to mold and mildew, and so on.” The fire-rated assemblies available for these products often require details that aren’t used in a gypsum assembly, such as gasket tape or an added batten strip of MgO board over the stud to prevent thermal transfer. As for mold and mildew, many gypsum wallboard products and cement boards score the maximum rating as non-nutrients for mold growth in testing using ASTM G21 or G22 standards. If the gypsum wallboard and the cement board to which MgO board is being compared score the maximum, how can MgO be “much improved”?
In addition, MgO panels are extremely rigid and dense, and unlike wallboard and cement board, cannot be single-scored and snapped with a standard utility knife. In reality, installation often requires the use of carbon-tipped tools, power tools and non-traditional finish methods. Add to this the fact that some MgO websites specify that fasteners should be located at least 2 inches from corners and no closer than ¾ of an inch from edges, which is difficult to do with standard studs being only 1-1/2 inches wide.
Finally, we are told that MgO panels are more flexible than cement boards. Again, generalizations can be misleading. Some cement board products, including National Gypsum’s PermaBase Flex Brand Cement Boards can bend to a 90-degree radius in as little as 6 inches; something MgO boards cannot do. And ¼-inch High Flex wallboard can produce curves in both directions in a single sheet, something MgO would have difficulty doing as well.
There may be applications where MgO board makes sense, but to position it as a “green/eco-friendly” product that is a “much-improved” alternative to gypsum wallboard or cement board is inaccurate and provides a disservice to your readers.
Product Manager, Cement Board
National Gypsum Company
W & C Responds:Throughout all of its 70-year history, Walls & Ceilings has kept readers informed of the newest products that hit, or “may” hit, the market place. We believe MgO board fits in the latter category.
We understand, and are fairly certain our readers also understand, that gypsum and cement board are, and will likely remain, the mainstay products of the industry for the foreseeable future. Nevertheless, if a new product such as MgO board can live up to the claims by the manufacturers, we consider it important that gypsum manufacturers and users of these items be aware of the new product. We readily acknowledge that many manufacturers are prone to expound on the benefits of their products and may neglect the possible drawbacks. In the event that something does slip by in any particular article in our magazine, we think that over time, our readers get an accurate understanding of products in our industry.
MgO board is very, very new in the United States, and we intend to be a source of accurate information about it in the future. We are grateful to our letter-writers for bringing this important insight about the product to our attention.
Walls & Ceilings Magazine