Will GFRC Make Conventional Concrete Obsolete?

Question:
The use of GFRC (glass-fiber-reinforced concrete) to make countertops seems to be growing. Will it eventually replace all forms of concrete countertops?

Answer:
There are two basic methods for casting concrete: pouring in place and precasting. Within the precasting method there are three basic variations: wet casting, hand packing and spraying. GFRC can be sprayed, just like shotcrete, or wet cast (called premix in the GFRC industry) exactly the same as conventional concrete.

Sprayed GFRC, or spray-up in industry lingo, is the preferred method for placing large expanses of GFRC material in short amounts of time because it’s efficient and speedy. Both the veneer coat (called a mist or face coat) and the backer coat are sprayed through a specialized gun. The speed and efficiency are realized in large part because of the machinery employed, not necessarily because of the material used.

GFRC in the concrete countertop industry is generally not placed using the same large, expensive machinery used in conventional spray-up. Rather it is a hybrid of spray-up, hand packing and sometimes wet casting. The mist coat is often sprayed using an inexpensive hopper gun, and the backer is either hand packed for vertical edges or wet cast using a more fluid version of the GFRC mix on horizontal surfaces. This difference seems insignificant, but it does affect the structural properties and the economy of using GFRC. Time is money, after all.

GFRC’s advantages are that it is fairly easy to execute, it produces robust pieces, and because it’s only a shell, it’s lighter. It can be used to cast any shape piece and is perhaps the best way to cast complex, three-dimensional pieces. But these features, though very attractive, do not make GFRC the best choice for all applications.

The flatter and more two-dimensional the piece (like a simple countertop), the less advantageous GFRC becomes. This has more to do with the time it takes to mix and place the material than the material itself. Plus, GFRC costs about three times the price of a from-scratch conventional concrete mix for equal volumes of material.

For some simple applications, especially smaller pieces like bathroom vanities, it can be cheaper and faster to wet cast conventional concrete rather than use GFRC, and the savings in weight of a few dozen pounds may not make much difference.

Visually, GFRC can have many looks, but it’s predominantly monolithic and monotextural in appearance. Some have criticized it for being too perfect, but certain techniques can be used to give it variation and mottling similar to that seen in wet casting. Troweling is one of the few techniques that I’ve not seen reproduced well in GFRC.

Concrete is an emotionally involving material for clients. Its customization, character and sheer essence draw them to it. Its look, variety and tactile qualities are unique, and something as simple as the sound a concrete countertop makes when a cup, glass or plate are placed on it or when knuckles are rapped against it has a profound influence on how some people react to the material. Solid concrete has a different feel and a different sound from GFRC, and that can make a difference to a client.

Each type of concrete and each casting technique has strengths and weaknesses, and some are more versatile than others. GFRC is a versatile tool. It can be used for a wide variety of applications, but choosing it for all applications may not be the best choice. Other factors such as time, cost, appearance and tactile sensation all play a part in which casting method is right for a particular project. Will GFRC replace all other forms of concrete? I doubt it, but it does remain to be seen how widespread its use will become.

For more details on basic GFRC casting techniques, read my article “Introduction to GFRC,” on the Concrete Connections website.