Calcium Silicate Block Insulation — Asbestos Exposure Crosswalk

What This Equipment Is

Calcium silicate block insulation is a rigid, white-to-light-gray, lightweight insulation manufactured by reacting lime, silica, and water at elevated temperature. The early formulations — sold from the late 1940s through the early 1970s — included chrysotile asbestos fiber (typically 5–15% by weight) as a structural reinforcement to control cracking during heating, cooling, and handling.

Calcium silicate progressively replaced 85% magnesia as the standard for high-temperature industrial insulation. Its service temperature range extends to 1,200°F or higher, making it the preferred insulation for boiler casings, steam-drum exteriors, turbine cylinders, superheater piping, reformer process equipment in refineries, and any other equipment running too hot for magnesia.

Major asbestos-bearing brand families included:

  • Kaylo — Owens-Illinois, then Owens-Corning Fiberglas, then Fibreboard
  • Unibestos — Pittsburgh Corning
  • Thermo-12 — Johns-Manville
  • Calsilite — generic / multiple producers

Calcium silicate was supplied as block (for boilers, vessels, ducts), pipe covering (sized to pipe ODs), and specialty shapes.

Why Calcium Silicate Block Work Was a High-Exposure Activity

Fresh calcium silicate is firm but workable — insulators cut it to fit with hand saws or power cutoff saws. Cutting released cut-edge fiber into the worker’s breathing zone. Joints were finished with insulating cement, mixed dry on-site.

In service, calcium silicate is more dimensionally stable than magnesia, but thermal cycling and aging still embrittles it over decades. Stripping aged calcium silicate from a boiler casing during an outage generates dense fiber concentrations from the broken sections and the powdery joint cement.

The legacy of asbestos-containing calcium silicate is large: most U.S. power plants and refineries built between roughly 1950 and 1975 are insulated with it, and substantial quantities remain in service today even where surface conditions look intact.

Manufacturers Named in Calcium Silicate Litigation

  • Owens-Corning / Fibreboard — Kaylo brand
  • Owens-Illinois — original Kaylo manufacturer (pre-1958)
  • Johns-Manville — Thermo-12 and other calcium silicate products
  • Pittsburgh Corning — Unibestos brand
  • Armstrong World Industries — Armstrong calcium silicate
  • Eagle-Picher — calcium silicate products
  • Combustion Engineering — insulation products

Documented Product References

Images sourced from publicly available product-identification reference materials. Inclusion does not constitute a finding of liability against any company.

Trust Funds That May Apply

  • Owens-Corning / Fibreboard Asbestos PI Trust (Kaylo)
  • Manville Personal Injury Settlement Trust (Thermo-12)
  • Pittsburgh Corning Corporation Asbestos PI Trust (Unibestos)
  • Armstrong World Industries Asbestos PI Settlement Trust
  • Eagle-Picher Industries PI Settlement Trust
  • Combustion Engineering 524(g) Asbestos PI Trust

Trades Most Exposed at Calcium Silicate Block Work

Insulators (Heat & Frost Insulators), pipefitters and boilermakers working alongside insulators, laborers doing tear-out, maintenance mechanics, and bystander trades in shared work areas.

Jobsites in the Network Documenting Calcium Silicate Use

Compiled from publicly filed asbestos litigation, EPA / state-DNR records, and industry-publication histories. Product and company references reflect what has been alleged or documented in publicly filed litigation. This page does not constitute a finding of liability against any company. Not legal advice; consult a licensed attorney about your specific situation.