As a countertop fabricator, you are familiar with the model of buying slabs or sheet goods and fabricating them to fit a space based on a template.

Concrete is different. As a material, it is highly malleable, both in concept and in practice. It is usually made from scratch with raw, elemental materials. Rock, sand, cement and pigments are combined to create the fluid mixture that is cast and shaped into the final product.

Concrete countertops are manufactured in two very different ways: cast in place and precast. Cast in place is similar to the types of concrete most of us are familiar with, such as sidewalks and foundations. With this method, fresh concrete is poured into forms built on site. For countertops, this means the forms are built on the cabinets, and the concrete is trowelled and finished in place.
 
Cast in place concrete is often used to create large pieces that are heavy, awkward or impossible to transport or install if they were precast. While cast in place allows for large, complex shapes, achieving a high quality product can be difficult. If an awareness and understanding of the client’s needs and expectations are not met, the resulting product can more closely resemble a sidewalk rather than a high quality countertop. And even if the countertop manufacturer has the skill and professionalism required, the constraints of working on a busy job site rather than in a controlled shop can make quality control difficult. One of the characteristics of cast in place concrete is that you don’t really know what you’ll get until it’s done, and then it’s often too difficult or expensive to change or fix it if the need arises.

Trowelling a cast in place concrete countertop.

Precast concrete countertops make up the bulk of the concrete countertops. Typically, precast concrete is formed, cast and finished in a shop, and then transported and installed on site. Templating is performed just like other countertop surfaces.

This concrete countertop production method allows for a much wider range of looks, design features and more often results in a higher quality product that is more in line with other countertop materials. Perhaps the only limitation to precast is the need to transport and install the pieces. As long as there are means to lift, move and handle the pieces, then they can be precast.
 

Summary of Manufacturing Methods

Precast

Cast in Place

Pros: Clients better understand this way of purchasing countertops. The process is “just like granite”, as far as they’re concerned. Easier quality control, plus the client doesn’t see the countertop until it’s done. Less mess in the client’s home or place of business. Wider range of looks, including embedded decorative aggregates. Cons: Requires a shop and more equipment. More seams required because you have to be able to transport the slabs.

Pros: Does not require a shop. Fewer seams. Cons: More difficult to obtain flat, straight, high-quality finish Less ability for quality control because the job site is not secured. Risk of damaging client’s home or place of business. Can’t make looks that require grinding, such as embedded decorative aggregates More challenging to make fancier effects such as integral sinks and edge returns.

 

Precast concrete has many different looks, and sometimes it’s not easy to identify that a particular countertop is actually concrete. There are three forms of precast concrete countertops: custom formed and poured (precast), custom formed and sprayed (GFRC), and purchased in slabs and fabricated (premade slabs).

The first two methods are what most people mean when they say “concrete countertop”. With these methods, no cutting is required, since each piece is formed to fit exactly where it will go. Because of the nature of concrete and the forming techniques, a wide variety of shapes, looks, colors, embedments, thicknesses and other features are possible. If a client wants a four inch thick, monolithic countertop, it can be made without the need for edge lamination.

Precast concrete vanities.

     
Precast concrete countertops are usually made thicker than other countertop materials. Often the concrete is 1.5” to 2” thick, and visually thicker pieces are manufactured with integrally cast drop down edges. This technique reduces weight, but very large pieces can still weigh several hundred pounds. One significant advantage that concrete offers is that it is a structural material. When properly designed, concrete can bear loads that other materials cannot.

8’ x 6” x 1.5” beam loaded with 500 lbs.	12” cantilever loaded with 960 lbs.

A relatively new precast technique for making concrete countertops is called GFRC, or glass fiber reinforced concrete. This technique uses a specialized concrete formula that is sprayed into forms. The manufacturing process is similar to fiberglass. GFRC provides structurally robust shells. GFRC’s strength is best realized with complex three-dimensional shapes that don’t need high structural capacity. Also, long or large slabs become more practical, since GFRC is made thinner and thus lighter than traditional precast concrete.

GFRC monolith

The third form of precast concrete countertops is premanufactured countertop sheets. While often marketed as recycled glass countertops, URBANSLABS™, IceStone®, Vetrazzo®, EnviroSLAB and other recycled glass countertop materials are really precast concrete. While the aggregates may be recycled glass, the material is concrete. Thus the performance and maintenance requirements are similar to other forms of concrete countertops.

These are specialized forms of concrete premade into finished sheets and are fabricated just like granite countertops. While branded as unique materials, the look and ecofriendliness can often be replicated with traditional precast concrete.

Summary of Types of Precast Concrete Countertops

1.    Precast

a.    Custom formed and poured.
b.    What people typically mean by “concrete countertop”

2.    GFRC:

a.    Custom formed and sprayed.
b.    A relatively new custom precast method.

3.    Premade slabs:

a.    Purchased in slabs and fabricated.
b.    Most similar to granite and solid surface fabricators’ processes.

About the Author:  Jeffrey Girard, P.E., is president and founder of The Concrete Countertop Institute, which provides training, information, advocacy and outreach for the concrete countertop industry. Visit www.ConcreteCountertopInstitute.com, www.ConcreteCountertops.net and www.ConcreteCountertopConference.com for more information about all of The Concrete Countertop Institute's programs.

The Concrete Countertop Institute
Training: www.ConcreteCountertopInstitute.com
Information: www.ConcreteCountertops.net
Networking: www.ConcreteCountertopConference.com
888-386-7711 phone
919-270-7693 direct
919-882-9700 fax