Grinders, scabblers and scarifiers

When concrete has to be resurfaced, the first steps in the process are often the most critical. For long-lasting repairs, the underlying concrete must be prepared properly to enable overlays or coatings to bond securely.

There are several tools and pieces of equipment that can prepare a concrete floor for a new finish or surface. Some of these machines and accessories overlap in function and can even be used in combination with each other. Many times the machine called for will be determined by the new material to be put on the prepared concrete.

Here's an overview of the different types of concrete resurfacing equipment available.

Grinders. There are two types of grinders: planetary and rotary. Planetary grinders typically use diamond-, ceramic- or silica-based abrasives to abrade surfaces such as concrete, stone, terrazzo and wood. They are used for many different applications like profiling concrete in preparation for a coating such as an epoxy or urethane.

"These grinders provide a very uniform surface free from gouging which makes them very easy to use without damaging the surface," says Travis McCutchen with Kut-Rite Mfg. "They're a perfect choice for rental.

"For example," he explains. "Concrete garage floors are being coated with epoxies at a rate of $4 per square foot. This is an awesome DIY project if the homeowner can rent a grinder that is easy to operate and will not damage the surface."

Polishing concrete is another popular application that is easily achieved with a light weight planetary grinder. John Abrahamson, president of HTC Inc., cautions that concrete polishing should be left to the professionals, however. "It takes a lot of training to properly polish a concrete floor," he explains. "A home-owner can't learn the skills in a quick lesson at the rental store."

On the other hand, re-sealing wood floors is a project that most homeowners would consider. The same grinder used on concrete with different abrasives can do the job. Lightweight planetary grinders are also ideal for removing lippage from wood decks, cleaning old and worn wood decks and general cleaning of concrete floors.

Like lightweight planetary grinders, rotary grinders typically use diamond-, ceramic- or silica-based abrasives to abrade surfaces such as concrete, stone, terrazzo. They are often used for creating a more aggressive profile or removing material. Some machines are equipped with a VFD (variable frequency drive) are can be used for high speed polishing.

"The rotary machines are heavier and operate at much higher rpm," says McCutchen. "Polishing concrete, stone and terrazzo with a high speed tool is a different approach that's much faster and provides a superior finish."

The 10- and 20-inch rotary machines are ideal for residential and light commercial surface preparation applications. They also perform well removing materials such as carpet glue, mastics and epoxies.

Scabblers use compressed air to hammer piston-mounted bits into the concrete surface. They tend to roughen the concrete surface more than grinding or scarifying. Some machines, like EDCO's Chip-Dek scabbler, can remove up to 1/4 inch of concrete in a single pass. The actual production rate depends on the strength of the concrete. A typical removal rate for a machine with a 12-inch working width is 200 to 250 square feet per hour at a 1/8-inch depth.

Scarifiers. Scarifying machines apply a cutting wheel to the concrete surface, leaving a clean, textured or roughed finish. Scarifiers are also referred to as planers, milling machines, rotary cutters or simply surface preparation machines.

These machines usually have various styles of interchangeable cutter assemblies that can be used for cleaning, grinding and light or heavy milling. Production rates range from 350 to 1,500 square feet per hour (depending on machine size and horsepower) for a 1/8-inch removal depth of 3,500-psi concrete.