The Trade That Lined America's Furnaces — With Asbestos-Bearing Refractory

Asbestos-bearing refractory, cut and mixed by hand

Through the asbestos era, much of the refractory brick, castable, gunning mix, and mortar used to line high-temperature equipment contained asbestos. Refractory masons cut and dressed refractory brick with saws and hammers, mixed dry castable and gunning material by hand and in mixers, and troweled asbestos-bearing mortar — releasing fiber directly into the breathing zone as they worked.

Tear-out and relining shutdowns

The periodic furnace, kiln, and boiler relining shutdown was the trade's highest-exposure work. Breaking out the old, degraded, friable refractory lining — often asbestos-bearing and baked hard — inside a hot, enclosed furnace with little ventilation produced some of the heaviest fiber releases of any construction trade.

Ceramic fiber and block insulation

Refractory linings were frequently backed by asbestos block insulation and, later, ceramic-fiber insulation, which the refractory mason installed and cut behind the brick and castable — another direct source of fiber.

Confined spaces and inadequate ventilation

The inside of a furnace, kiln, or boiler being relined is a hot, dusty, confined space. Fiber released during refractory tear-out and installation had nowhere to go, and the refractory mason breathed it for the length of the shutdown.

Respiratory protection came too late

OSHA's first asbestos exposure regulations were promulgated in 1971 — after decades of refractory masons handling asbestos-bearing refractory. Even after 1971, enforcement was uneven; respirators were available but their use was not consistently required or even encouraged on industrial worksites. Most refractory masons who entered the trade between 1940 and 1975 — now in their 70s and 80s — completed their careers with very little respiratory protection at all.

The occupational-health record

Dr. Irving Selikoff's Mount Sinai research documented elevated mesothelioma incidence across the trades that handled asbestos-bearing materials in confined industrial spaces. The disease pipeline, driven by mesothelioma's 20-to-50-year latency between exposure and diagnosis, continues today — the cohort that worked the asbestos-refractory era is being diagnosed now, and will be for the next two decades.

1865 — The founding

The Bricklayers' International Union — today the International Union of Bricklayers and Allied Craftworkers (BAC) — was chartered in 1865, making it one of the oldest trade unions in North America. The craft grew alongside the buildout of the country's first generation of blast furnaces, open-hearth steel plants, cement kilns, glass melter tanks, coke batteries, and industrial boilers.

1900s–1940s — Growth with high-temperature industry

Every furnace, kiln, and boiler that ran hot required a refractory interior lining to survive operating temperatures from 1,800°F in kilns to over 3,000°F in steel and glass service. The refractory-mason branch of the trade built and relined those linings — and manufacturers formulated much of the era's refractory brick, castable, and gunning mix with asbestos for its heat and thermal-shock resistance.

1940s–1970s — Peak membership and peak exposure

The postwar industrial buildout — expanding steel mills, cement plants, glass plants, and power stations — put refractory masons on constant furnace-relining and coke-oven work with asbestos-bearing refractory. The trade's exposure was at its highest concentration during exactly the era now showing the highest mesothelioma incidence rates among retirees.

1970s — Federal recognition

OSHA's 1971 asbestos exposure regulations followed the Mount Sinai cohort studies documenting elevated mesothelioma rates across the industrial trades. Through the 1970s and 1980s, non-asbestos refractory and insulation formulations replaced the asbestos products in new work.

1980s–today — Post-asbestos era

By the 1980s, asbestos was substantially phased out of refractory and insulation products. Refractory masons who entered the trade after that worked under a substantially safer regime — but the disease pipeline from the 1940s-1970s cohort continues, and relining shutdowns that removed legacy asbestos refractory from older furnaces extended exposure for some into later decades. The next two decades will continue to draw heavily from the asbestos-era cohort.