GFRC COUNTERTOP CONSTRUCTION

Date posted: 29/08/2017

Glass-fiber reinforced concrete (GFRC) isn't new to the concrete industry but its use in concrete countertops is a recent phenomenon. GFRC provides increased tensile and flexural strength, reducing the possibility of cracking, even at the narrow inside corner openings for a sink.

As a decorative precast contractor, TRENDCONCRETE switched to GFRC six years ago for constructing countertops, specialty floor tiles, and architectural pieces, because of its benefits:

 

GFRC castings weigh less because they are made thinner.

Only a mold surface for one side of a casting is needed.

Steel reinforcement isn't necessary, which eliminates the time-consuming process of constructing reinforcement cages.

Mechanical vibration is not required, even for complex shapes, and there are virtually no bug holes.

Transporting work costs less with little risk of cracking.

 

 

Chopped glass fiber is introduced after concrete ingredients are mixed.

Most importantly, switching to GFRC offered Gore the opportunity to expand his business to an international market.

 

Types of glass fiber

 

Fiberglass is sensitive to the high alkalinity of concrete so the manufacturer coats the glass fiber to prevent them from coming in contact with cement paste. Typically referred to as alkaline resistant (AR) fibers, these should be used for GFRC work. Do not use type A or E fibers.

Glass fibers are sold as individual fibers, as fibers bundled in multifilament strands, or as mats that are placed in a mix and covered with wet concrete. Individual “chopped” fibers can be purchased in lengths up to 1 1/2 inches long, however, Gore prefers 1/2-inch lengths for his projects. When contractors buy bales of multifilament strand, they can chop them into desired lengths with a glass fiber chopper gun mounted at the end of a shotcrete spray nozzle. As the concrete mix is pumped through the nozzle, it is accelerated by compressed air and mixed with the GFRC fibers as it travels toward a mold.

 

 

In order to prevent AR glass fibers from showing on the surface, workers use a hopper gun to spray a slurry coat against form surfaces before placing GFRC.


Casting a countertop

 

The first step is to place a slurry coat without glass fibers directly onto the mold surfaces. This prevents the glass fibers from being visible on the surface of the finished product. The thickness of this application is usually 1/8 to 1/4 inch thick and can be sprayed on with a hopper gun or other spraying equipment. TC waits for the water sheen of the mix to disappear before placing the GFRC application. You also can lightly push your finger into the mix; if nothing sticks to your finger it is ready.