USG Casting Fireplace Surrounds - Manual (Page 14)

Fiber reinforcement should always be used when manufacturing
fireplace surrounds. Glass fiber matting and/or chopped glass fiber
strands can be used for hand-layup and spray processes. The
recommended proportion of fibers is 5% - 6% of the weight of the
mix. (See Manufacturing.) This proportion provides increased
impact strength, flexural strength, and resistance to breakage during
shipping, handling, and installation. Using glass fiber will also
minimize the potential for cracking during normal use.
A Surround without Fiber Reinforcement Exhibits Cracking During Thermal Testing
There are several different types of glass fibers. Use fibers that are compatible with the gypsum cements you are
using, as some alkaline gypsum cement formulations can have a detrimental effect on fibers. To maximize the ben-
efits of fiber reinforcement, review fiber thickness and chopped lengths. The type of fabrication process you use will
also determine the type of fibers you need. Your USG sales representative can help with selection of the best fibers
for your specific products.
Production
Fiber Reinforcement
14 Casting Fireplace Surrounds