Shot Blasters and Surface Preparation

A shot blaster fire scores of tiny BB’s at the ground over and over again. It duplicates a simple mechanical action — a metal object hitting a crushable piece of material — and duplicates it very, very quickly. If you want to tear a layer off a slab of concrete, these machines will certainly do the job.

But shot blasters have the same downside as shotguns: The end result is not exactly tidy.

That’s not a problem if you’re prepping a new warehouse floor for a thick layer of epoxy. But for decorative concrete contractors who shot blast, the questions “why,” “when,” and “how” are much more crucial.

A shot blaster is the tool of choice for concrete contractors when prepping a surface, says Greg Ferchaud, national sales manager for SASE Co. Inc., which distributes Italian-made Trimmer shot blasters. Shot blasting gives the surface a rough profile so coatings and sealers will bond snugly with a floor. “You scarify, diamond grind or shot blast — that’s how you prep a floor,” he says. “Shot blasting requires the most attention of the three. It can be the most productive, but it requires the most parts to be replaced.”

Shot blasters were developed to scour nonskid coatings off the steel decks of aircraft carriers. When it comes to concrete, most shot blasters are used on large industrial and commercial jobs, from cleaning parking lots to scouring line stripes off highways. “To come into a residential home and use a shot blaster is pretty rare,” Ferchaud says.

But small-job contractors use them too. The rough profile guarantees a good bond, and the work can be done in a fraction of the time it can take with other equipment.

Shot blasters can be used to blast decorative garage floors before coating. On new construction sites, they can scrape the dusty top surface off rained-on concrete. They have even been used to stencil patterns, from company logos to leaves and seashells, on concrete.

Shot blasting is essential before applying an overlay, says Dave Pettigrew of Diamond D Concrete. “Some manufacturers won’t even warranty their product without blasting,” Pettigrew says. “You have to give the existing concrete a tooth so you can attach to it.”

Give it a shot
Trevor Risher’s Seattle-based outfit, Washington Shotblasting, shoots five million square feet a year, much of it as a sub for small or mid-size contractors. “I have different shot blasters for different types of jobs,” he says.

A good machine costs $30,000, he says, so if a contractor only blasts one job a year, it may be more cost-effective to hire a specialist like himself. But he acknowledges he occasionally loses good clients when they finally decide to buy their own machines.

Let’s say you’ve reached that point — you expect to use a shot blaster on at least four or five jobs a year, so buying one makes sense. How do you go about shopping for one?

Bruce Williams, owner of B W Manufacturing Inc., based in Grand Rapids, Mich., says shoppers should look at reliability, production rate, and ease of maintenance and servicing. “A lot of times what I do is refer people to owners of the equipment,” he says.

Allen Slater, product specialist with Blastrac, a leading manufacturer of shot blasters, says five variables impact each blasting project: the travel speed of the propulsion device; the quantity and size of the abrasive; the tenacity of the coating to be removed; the desired end result; and the size of the machine.

However, he says, the most important question is a basic one: How many square feet of production do you need per hour?

Machines with blast widths between 10 inches to 30 inches will cost roughly the same, he says, but below 10 inches, the price drips drastically.