Narco Gunning Mixes CM-343 / CR-346 / MCD-344 / P-340 / MC-339 (1964–1977)

Product Description

Between 1964 and 1977, North American Refractories Company — commonly known as Narco — manufactured and sold a line of asbestos-containing refractory gunning mixes under the product designations CM-343, CR-346, MCD-344, P-340, and MC-339. These products were engineered for use in high-temperature industrial environments, where they were applied by pneumatic spray — or “gunning” — equipment to line, patch, and repair furnaces, kilns, boilers, ladles, and other refractory structures.

Refractory gunning mixes serve a specialized purpose in heavy industry. Unlike preformed refractory brick, gunning mixes are dry or semi-dry blended materials that are conveyed through a hose and nozzle under pressure, then deposited onto a target surface where they bond and cure to form a heat-resistant lining. The gunning process allows refractory materials to be applied quickly in difficult-to-reach areas, around curved surfaces, and during partial shutdowns when equipment cannot be fully cooled. This made Narco’s CM-343, CR-346, MCD-344, P-340, and MC-339 products practical choices for maintenance crews and construction contractors working in steel mills, foundries, cement plants, glass manufacturing facilities, chemical processing plants, and other industries that relied on high-temperature process equipment.

Narco was a prominent supplier in the North American refractory market during this era, and its gunning mix product line was distributed broadly across industrial sectors throughout the United States.

Asbestos Content

Trust fund documentation associated with the North American Refractories Company Asbestos PI Trust confirms that the CM-343, CR-346, MCD-344, P-340, and MC-339 gunning mixes contained asbestos as a formulated component. Asbestos was incorporated into refractory gunning mixes during this period for several functional reasons: it improved the tensile strength of the cured lining, reduced cracking and spalling under thermal cycling, enhanced adhesion to vertical and overhead surfaces during application, and contributed to the overall insulating performance of the finished product.

The precise fiber type and percentage by weight present in each specific Narco gunning mix designation may vary and is best confirmed through trust fund claims documentation, Material Safety Data Sheet records from the production period, or product specification sheets maintained in litigation discovery archives. What is confirmed across trust fund records is that these five product lines, as manufactured by Narco during the 1964–1977 production window, are recognized asbestos-containing products eligible for claims against the North American Refractories Company Asbestos PI Trust.

How Workers Were Exposed

Workers who handled, applied, or worked in proximity to Narco’s CM-343, CR-346, MCD-344, P-340, and MC-339 gunning mixes faced significant potential for asbestos fiber exposure across multiple stages of product use.

Mixing and Loading Before application, gunning mixes were measured out, blended, or loaded into hopper equipment. Pouring, scooping, or opening bags of dry refractory gunning material released airborne dust that could contain respirable asbestos fibers. Workers who handled the bagged product or prepared the mix for the gunning machine were directly in the dust cloud generated during these steps.

Gunning Application The pneumatic application process itself was a primary route of exposure. As the mix was propelled through the hose and nozzle under compressed air, fine particulate matter — including asbestos fibers — became airborne in the work area. Nozzle operators and assistants working in close proximity to the application point faced direct inhalation exposure. In enclosed or partially enclosed spaces such as furnace interiors, ladle linings, or boiler fireboxes, airborne fiber concentrations could build to elevated levels without adequate ventilation.

Rebound and Overspray A characteristic of the gunning process is “rebound” — material that does not adhere to the target surface and falls or bounces back into the work area. Rebound from asbestos-containing gunning mixes created a secondary source of airborne dust and surface contamination that affected not only the nozzle operator but also crew members nearby.

Demolition, Repair, and Relining When furnace or kiln linings applied with Narco gunning mixes required repair or replacement, workers engaged in scarfing, chipping, jack-hammering, or otherwise breaking out the hardened refractory material. Disturbing cured asbestos-containing refractory produced substantial quantities of fibrous dust. Maintenance crews, refractory bricklayers, boilermakers, and ironworkers who performed tearout work on previously gunned linings were exposed even if they had never handled the original product themselves.

Bystander and General Industrial Exposure Industrial workers generally — including pipefitters, electricians, millwrights, and other tradespeople who shared work areas where Narco gunning products were being applied or demolished — could be exposed as bystanders without being directly involved in the refractory work. In active steel mill or foundry environments, gunning operations were often performed concurrent with other maintenance activities, making bystander exposure a documented concern across multiple trades.

Asbestos fibers inhaled or ingested during occupational exposure can remain in lung tissue and the lining of the chest and abdominal cavity for decades. Diseases associated with asbestos exposure — including mesothelioma, asbestos-related lung cancer, asbestosis, and pleural disease — typically carry latency periods of 20 to 50 years between initial exposure and clinical diagnosis.

This article is provided for informational and reference purposes. It does not constitute legal advice. Individuals seeking compensation for asbestos-related illness should consult a qualified asbestos attorney.

Documented Product Identification

The following details are drawn from public asbestos litigation records, manufacturer catalog pages, technical manuals, and corporate history materials. Each item reflects the product as documented in those sources.

Corporate context: Formed in 1929 through the merger of several refractory companies including Queen’s Run, Crescent, and Eltra, among others. Owned by Eltra until 1979, then by Allied Signal (Allied) from 1979 to 1986, after which ownership transferred to banks and investors. Headquartered in Cleveland, Ohio.

Brand identification: Narco

Industries served: steel, iron.

North American Refractories Company (Narco) manufactured refractory materials used primarily in high-temperature industrial applications such as steel and iron processing. The company operated approximately eleven manufacturing facilities and a research center in Curwensville, Pennsylvania.