After supplier quotes for the 1,000 ornamental balusters in a
planned luxury home’s porch railings (1) came in at $150
apiece, BOJ Construction of Boston decided to look elsewhere
— namely in-house. With the help of outside mentoring and
some hands-on training in how to work with molded high-density
polyurethane foam, the company’s craftsmen launched their
From a casting of a lathe-turned baluster prototype (2) they
created a two-part silicone mold. The mold is filled with
liquid urethane (3), closed, and set in a sturdy LVL press (4).
The press resists the considerable pressure exerted as the
closed-cell foam expands inside the mold; with nowhere to
expand to, the foam cures at a density close to that of
mahogany. Complete curing takes about 15 minutes.
One-inch-diameter aluminum tubes cast in the core give the
cured balusters lateral stiffness (5).
The final cost per baluster worked out to about 50 percent of
that quoted, with equipment and setup costs running around
$4,000. BOJ has since used the technology to reproduce
carvings, corbels, and moldings for its historic restoration
work and now accepts custom commissions from other builders.
— Dave Holbrook