In the Slippery Rock Gazette August 2010 issue, Jeff Girard, president and founder of The Concrete Countertop Institute in Phoenix, Arizona, outlined the three methods of manufacturing concrete countertops: pre-manufactured slabs, castin-place and custom precast.
This article details the custom precast methods and explains important considerations for stone fabricators considering adding concrete to their offerings.
There are three types of custom precast countertops: wet cast, hand packed and GFRC (glass fiber reinforced concrete). Each has its own unique mix design, casting method and finished look.
"Wet cast" precast concrete countertops use a traditional concrete mix composed of sand, aggregate, cement, water and speciality admixtures. The concrete is made flowable enough to vibrate and get most of the air bubbles out. Typically, fabricators attempt to create a perfect casting, so that almost no work needs to be done to the concrete once cured, other than sealing. While this seems appealing, in practice it is nearly impossible to create a perfect casting. This technique necessitates making forms that are water tight and perfectly smooth, adding a great deal of time to the process. Three-dimensional shapes require two-sided molds.
"Hand packed" or "hand pressed" concrete countertops are made using an almost clay-like mix that does not use aggregate and is not vibrated. The concrete can be placed into forms to deliberately leave large, patterned voids that are later filled in with contrasting cement grout. Or, the concrete can be packed into forms to form a smooth surface. This technique makes forming quick and easy, but it requires grinding and grouting of the finished concrete to fill in holes. Three-dimensional shapes are easier than with wet cast, requiring only one-sided molds
A relatively new technique using glass fiber reinforced concrete (GFRC) is becoming very popular in the concrete countertop industry. GFRC is a form of concrete that uses fine sand, cement, acrylic polymer, water, other admixtures and alkali-resistant (AR) glass fibers. A thin face coat with no fibers is sprayed on the surface, then a backer coat containing large amounts of AR glass fibers is applied. This results in an extremely strong, relatively flexible, lightweight countertop. GFRC countertops can be made as thin as, with a false edge of 1- or more.
GFRC concrete countertops have many advantages over the other two types of precast concrete countertops:
Large pieces with no seams Lightweight Flexible Require only one-sided molds Easy to create intricate, three-dimensional shapes Require less expensive equipment Faster turnaround time
Any type of precast concrete is a departure for stone fabricators, since the material is made in the shop, not cut from slabs. However, many stone fabricators are finding that GFRC is the easiest way to add concrete to their offerings.
Dustin Braudway, owner of Bluewater Surfaces in Wilmington, NC, has been trained in both hand packed and GFRC techniques. "GFRC is hands down easier for me than hand packed. The equipment is smaller, it's faster, and I can really expand my offerings beyond stone and quartz, with large, complex projects," Braudway reports.
Evan Kruger, owner of SolidTops in Easton, MD, agrees. "I have several years of experience fabricating various recycled glass concrete slabs. I became interested in custom concrete, and then GFRC, because it gives me far greater quality control and design freedom."
Whatever style of working with concrete you choose, it is important to consider startup costs, equipment and space requirements, speed of fabrication, design flexibility and the capabilities of your staff. Many stone fabricators have found that GFRC fits best in their shops, but only by becoming educated about concrete can you make the choice that's right for you and for your customers.