What's in Homasote® Board in Addition to Post-Consumer Paper?

by Doug Woerner
Homasote Company Product Development Engineer

We're often asked about the materials we use to manufacture Homasote &endash; what they are and their purpose.

Paper comprises more than 98 percent of Homasote board and is its structural component, with nearly all board strength derived from bonding of cellulose fibers to each other.

The wax we use in manufacturing, a liquid emulsion of wax and water, provides water resistance to the final product. In manufacturing, the wax is separated from the water by alum and then deposited onto the cellulose fibers. During drying, the wax melts and is absorbed by the cellulose fibers.

Another water emulsion, retention-aid polymer, improves water drainage and retention of solids. It does this mainly by chemically coagulating or flocculating the fibers and the fine particles.

Talc is primarily a process aid. It helps to keep the mold screens clean by attaching to "stickies," such as glue, oil, asphalt, etc.

Rosin has both product and process functions. It adds board strength and helps to keep the mold screens clean by attaching to fine and sticky particles.

Aluminum sulfate (alum) has one simple but critical function, separating wax from the emulsion, making it available to deposit on the cellulose fibers.

Hydrated alumina (aluminum trihydrate), is used only in 550, N.C.F.R., as a fire retardant. It decreases the flammability and smoke emission dramatically.

Starch, used only on 460 board, is a binder or adhesive that increases board strength by forming a stronger bond with the cellulose fibers.