Track 7: FIRE, Presentation 1
A Stitch in Time: How Fire-Retardant-Treated Wood Helped Save the Washington Monument
Mike Eckhoff, PhD
Hoover Treated Wood Products, Inc.
meckhoff@frtw.com
Fire-retardant-treated wood (FRTW) products are any wood products that exhibit reduced surface-burning characteristics and resist the propagation of fire when impregnated with chemicals. Fire-retardant treatment of wood improves fire performance by greatly reducing the amount of flammable gases released, thus reducing the rate at which flames spread over the surface. Treatments reduce the amount of heat available or released by the volatiles during the initial stages of fire and result in the wood self-extinguishing once the primary source of external fuel is exhausted. FRTW’s effectiveness has been demonstrated through various military and civilian projects over the past century, including as the decking material for the U.S.S. Nashville (PG-7) and the U.S.S. Maine (ACR-1) in the late 1800s, the scaffolding and formwork for concrete buildings constructed for the 1939 New York World’s Fair, and for 17 dirigible hangars built in the U.S. during World War II. Perhaps the most unrealized but most recognizable example of how FRTW has been used is the Public Works Administration’s Project Number 365—the emergency repair of the Washington Monument in Washington, D.C., in 1934.
Construction on the Monument began when its cornerstone, a donated 24,500-pound block of coarse-grained Texas marble from a quarry located near Texas, Maryland, was laid on July 4, 1848. Controversy in the mid-1850s and the outbreak of the Civil War caused construction to stall until the nation’s Centennial, when Congress charged the U.S. Army Corps of Engineers (ACE) with finishing the Monument, albeit with a simpler single-obelisk design. However, the original quarry had closed, leaving the ACE scrambling for a replacement. The ACE chose to initially clad using dolomitic Stockbridge marble from a quarry in Sheffield, Massachusetts. Problems with stone quality and delivery delays led the ACE to switch to a fine-grained Cockeysville marble from a quarry near Baltimore, Maryland, in 1880, which was used to finish the obelisk’s exterior in 1884. To this day, all three types of marble can be seen by their different colors on the Monument’s exterior.
By the time the National Park Service (NPS) was given jurisdiction over the Monument from the ACE in 1933, the agency had to address a half-century’s worth of neglect. The different types of marble and construction techniques used over the prior century meant the Monument’s mortar was more prone to spalling. For years, this spalling allowed rainwater to seep into the Monument’s walls, through the outer marble layer and into the inner granite layer, putting its structural integrity into jeopardy.
The NPS responded with a $100,000 appropriation via the Depression Era’s Public Works Administration (Project No. 365), which would pay for cleaning and repairing the Monument and for the necessary scaffolding. The scaffolding would be constructed of steel pipe with vertical panel joints spaced to allow for placing the wood plank platforms sufficiently close enough to the Monument to complete the work. The wood planks were required by the NPS to be “thoroughly preserved against fire by impregnation with chemicals.” In other words, only FRTW would work. At the time, a Class D fire-retardant treatment is what was recommended for scaffolding. However, engineers in the NPS concluded that a stronger Class C fire-retardant treatment, which is designed more for “structural timber” applications and would “not appreciably weaken the wood or cause staining on the marble” due to leaching from rain or the cleaning operations, would be needed. Approximately 60,000 board feet of Class C Douglas fir FRTW dimensional lumber were used in 13 platforms to repair the Monument. Thanks to the use of and the inherent safety of the FRTW, the Washington Monument was repaired in just five months, remained open to visitors while being repaired, and remains standing today.
Mike Eckhoff is a public policy expert with nearly 20 years of experience in the forest products industry. Since 2017, he has been a Codes and Education Specialist for Hoover Treated Wood Products, Inc., providing technical expertise on fire-retardant-treated wood (FRTW) to architects (AIA-accredited seminars; HSW credit), building/fire officials (ICC Preferred Education Provider), designers, engineers, foresters, students, and wildland firefighters. He has written over a dozen peer-reviewed articles and has given hundreds of invited presentations to firms, agencies, and other audiences throughout the U.S., all with a focus on sustainable wood products, including FRTW, and how they improve forest health and reduce wildfire risks simultaneously.
