Concrete, as most folks know, is strong under compression but weak under tension, and is commonly strengthened by casting it around, e.g. a grid of steel reinforcing bar (“re-bar”). Glass Fiber Reinforced Concrete is, well, pretty much exactly what it sounds like: concrete reinforced with glass fibers. As in most composite materials, the fiber elements in GFRC can be carefully oriented, or randomly distributed, in the solid matrix. The nice thing about the latter method is that you can just mix the reinforcing fibers into the bulk concrete and don’t have to pre-position them in the mold. GFRC concrete panels can be much thinner and lighter than metal-reinforced slabs, and the glass fibers are not subject to corrosion.

If you’re interested in experimenting with GFRC, however, you may have noticed that practical how-to information is a bit scarce online. The notable exception, IMHO, is this pair of hands-on tutorials from Brandon Gore (who produced the cool concrete coffee table with cast-in saucers we hit last Friday), first published in Concrete Decor magazine in the summer of 2008 and now freely available on their website.

In the first, Brandon details three different concrete mix recipes used in the casting of a GFRC bathroom counter with integral sink. These are the “face coat,” which is sprayed in to line the mold and does not contain fibers, the “vertical backing coat,” which is applied behind the face coat to the panel’s upright surfaces, and the “self-consolidating backing coat,” which fills in the rest. In the second article, Brandon covers the process of actually applying the mixtures to the mold. [Thanks, Brandon!]

Concrete Decor – GFRC Mix Design
Concrete Decor – GFRC Application