How to Buy Concrete Surface Preparation Equipment - Buyer's GuideWhether you need to grind, scarify, mill or blast your way to a properly prepared surface, here's advice on finding a machine that can do the job efficiently and with less messPreparing concrete surfaces for coatings, overlays, stains or repair materials is a time-consuming task that many contractors perform begrudgingly or are tempted to overlook altogether. But if you've ever skipped this essential first step in the process, you undoubtedly learned the hard way how critical it is to the success of the job. Achieving a beautiful, smooth surface requires the right surface prepartion equipment. Advanced Concrete Enhancement in Sun Valley, CA "Lack of surface preparation causes 90% or more of overlay failures," says technical expert Chris Sullivan of Sullivan's Corner. "The surface needs sufficient 'bite' for the overlay to bond, otherwise delaminating failure can result." Sullivan contends that for most decorative overlay projects, contractors should devote more time to surface prep than to the actual overlay installation itself. Fortunately, an arsenal of high-performance equipment is available that can help you make the most efficient use of this time, enabling you to achieve the exact surface profile you need with less effort and mess than ever before possible. The most effective weapons for getting your concrete floors into shape are shotblasters, concrete grinders and scarifiers. Within these equipment categories, you'll find a wide array of models with applications as diverse as the products themselves, from compact handheld units for small jobs or working in tight spots to high-productivity ride-on machines for covering large expanses quickly. Many of these machines also come with an assortment of attachments, allowing you to remove a variety of different coatings and perform profiling tasks ranging from light roughening to aggressive milling. And in many cases, there's no need to worry about dust and debris. Machines that use dry-cutting methods usually have dust-collection capabilities, minimizing the cleanup work necessary before you apply a decorative treatment to the surface. To help you explore all these options, here's a guide to some of the latest surface prep powerhouses on the market, along with a few tips from manufacturers for achieving the best results when using their equipment. MATCHING THE MACHINE TO THE JOB Let's address the most important question first: Do you really need an expensive piece of equipment to strip off old coatings and prepare concrete surfaces for coatings and toppings? Actually, you may be able to get by without one. In some cases, acid etching or chemical strippers will do the job (see What About Acid Etching for Surface Preparation?). However, in most situations the best way to remove contaminants and unsound concrete is by mechanical means. A good surface prep machine will break up existing sealers, coatings or adhesives with no chemicals involved. It will also lightly pulverize the surface, leaving a roughened profile for overlays and toppings to grab on to. And unlike acid etching, mechanical abrasion can level uneven joints or high spots, polish rough or worn floors, smooth out trowel marks, and remove spalling or delamination.
Obtaining the right concrete surface profile, or CSP, is especially important when applying a new coating or overlay (see What's a Concrete Surface Profile, or CSP?). You have to achieve a profile deep enough to lock in the coating and ensure a good bond without going so deep that the coating won't be thick enough to hide your profiling work. The key to achieving good results is to match the equipment (and attachment) to the job at hand. But the decision isn't always clear-cut. For some jobs, there may be a number of viable solutions or you may need to use a combination of methods, such as shotblasting in open areas and hand grinding along edges and in corners. Because each type of machine takes a different approach to surface preparation, some units are better suited than others for certain tasks. Although this guide gives you a general overview of how the various machines operate and what they can accomplish, always consult with the equipment manufacturer, who can help you determine the best fit for a particular project (see Ten Factors to Consider When Selecting Equipment). Many rental companies and dealers also have specialists available to answer your questions or arrange for an equipment demonstration. If possible, test out various types of equipment in a small area of your slab to determine which machine obtains the desired results. SHOTBLASTERS How they work Shotblasting is a one-step method for stripping, cleaning and profiling surfaces in preparation for coatings and overlays. Not only do shotblasting systems produce a roughened texture that improves adhesion of decorative toppings, they also leave surfaces dry and immediately ready for recoating or resurfacing. Concrete shot blasting machine from Blastrac. Most shotblasters use a wheel with paddle-type blades that propel steel shot at the surface at a high velocity using centrifugal force, fracturing off the surface layer of the concrete along with any dirt, coatings, paint or other contaminants. The entire process is confined in an enclosed blast chamber that recovers and separates the dust from the spent steel shot. The removed debris is sent to a separate dust collector while the reusable abrasive is recirculated. The depth of surface removal is controlled by a combination of factors, including the size of the shot and concentration used, the rate of machine travel, shot impact force and whether you need to strip away an existing coating. Shotblasters are typically walk-behind or ride-on units, with blasting paths ranging from 4 to 32 inches and removal rates from about 200 to over 3,000 square feet per hour. Smaller models are good for working in tight areas, such as around equipment and obstructions and next to walls, and for preparing residential garage floors or balconies for decorative coatings. The most common power options are electric, diesel and gasoline. Typical applications Shotblasters can perform surface preparation tasks ranging from very light etching to more aggressive removal of surface mortar down to coarse aggregate. They also are a cost-effective method for removing dirt, grime and chemical contaminants from large areas and for prepping substrates for self-leveling or polymer overlays, epoxy toppings and most coatings. Another big advantage of shotblasting is that it produces very little airborne dust or debris, making the method a good choice for floors in sensitive areas, such as food preparation facilities or manufacturing plants. What shotblasters can't do effectively is remove rubbery mastics or heavy elastomeric coatings, because the steel shot will just bounce off the surface. Tips for best results
GRINDERS How they work Grinders use horizontally rotating discs to perform a multitude of tasks, from light texturing to open the pores of the surface to removal of paints and thin coatings. The key to their versatility are the grinding attachments, which are available in a variety of types and grits to suit different applications. Because grinders use rotary action rather than impact to remove material, the depth of material removal is limited to about 1/8 inch, depending on the type of attachment used. They generally leave behind a smoother profile than scarifying or shotblasting, and when working on hard, dense concrete they may polish rather than abrade the surface. Surface Pro® 650 Heavy Duty Grinders from GranQuartz in Atlanta, GA For floor and slab surfaces, you can find walk-behind grinders ranging in size from single-disc units for working in small or restricted areas to dual-, triple- or even four-disc machines for high-production grinding of large slabs. A single-disc grinder has a working width of 10 to 12 inches while a dual-disc unit covers 20 or more inches in one pass. Disc rotation speeds range from about 250 to over 3,000 rpm. On multiple-disc units, the discs usually are counter-rotating to provide balanced torque so the grinder won't pull from side to side. For more even grinding, some machines are also equipped with floating heads that will follow the contour of the floor and adjustable rear wheels to keep the grinding discs level. Many manufacturers offer a choice of power options, including electric, gasoline and propane. Most machines are equipped with vacuum ports for dust-free dry grinding. Some models also include water mist systems so they can be used with wet- or dry-cutting attachments. Gear driven grinder from Levetec in Redmond, WA Although walk-behind machines are well suited for profiling large slab surfaces, you can also buy handheld grinders for working in tight areas where larger units can't maneuver, such as in corners and close to walls. These smaller workhorsesare available with grinding diameters ranging from 5 to 12 inches and can also be used to remove bumps, form marks, and graffiti from vertical surfaces or to grind concrete countertops (see A Definitive Polisher for Concrete). Like their larger cousins, handheld units come with a selection of grinding accessories and can be hooked up to an industrial vac for dust control. Typical applications Many of today's grinders can serve multiple functions and are generally more adaptable than other types of surface prep equipment, especially when it comes to decorative work. They are a good solution for profiling floors before application of thin coatings or paints because they won't create ridges in the surface, as can scarifiers. Other applications include breaking up deposits of grease, dirt and industrial contaminants and leveling uneven joints or high spots. Many contractors also use grinders with finer-grit abrasives to polish concrete surfaces. Attachment options Investing in an assortment of attachments for your grinder will maximize its versatility and allow you to perform a broader range of tasks with one machine. The three most common types of grinding attachments are silicon-carbide-impregnated grinding stones, tungsten-carbide inserts, and diamond-segmented grinding tools. Some grinders are also available with scarifying attachments for removing thicker coatings and mastics. Available in various grits for coarse or fine polishing, silicon-carbide stones are an economical choice for such applications as smoothing trowel marks or rough finishes and leveling high spots less than 1/16 inch. However, these stones can clog easily, which can make them inefficient at removing most coatings. Tungsten-carbide inserts and diamond grinding accessories remove surface coatings with greater speed and efficiency. Tungsten-carbide inserts are carbide-tipped blocks with beveled edges that can strip heavier buildups or coatings without digging into the concrete. Their removal action, which is similar to using a scraper, works best in materials thicker than 1/16 inch. Applications include removing adhesives, thick paints, resins, tar, industrial buildups and rubber deposits. Diamond disc attachments from GranQuartz in Atlanta, GA For profiling work and removal of thin-film coatings or coatings with high hardness values, such as urethanes and epoxies, diamond-segmented abrasives are generally the best solution. Other applications include polishing and removing minor surface imperfections. The diamond segments, which are bonded to a backing plate or to removable block inserts or plugs, sit on the surface and are embedded in a metal or resin matrix. During grinding, the matrix wears away gradually to expose new diamonds. You can choose diamond tooling in various grit levels, ranging from fine to coarse, and with different bond hardnesses, shapes and diamond concentrations, allowing you to match the tool to your project requirements. Regardless of the attachment you use, look for inserts or grinding discs that are easily replaceable. This will allow you to move more easily from coarser to finer grit levels. Tips for best results
SCARIFIERS How they work Scarifiers, also called surface planers or milling machines, remove concrete faster and more aggressively than grinders. That's because they use the pummeling action of multi-tipped cutting wheels, or flails, that rotate at high speeds to chip away at the concrete surface. You can choose from many different styles of interchangeable cutter assemblies to achieve the profile you need for each job. Roto-Star scarifier from GrindAll Surfaces in Cleveland, OH Equipment choices range from small handheld units with 2- to 3-inch cutting widths to manual push or self-propelled walk-behind machines with working paths of 4 to16 inches. Production rates for walk-behind models range from 350 to 1,500 square feet per hour, depending on machine size and horsepower, material to be removed, hardness of the concrete and type of cutter used. Cutting depths are adjustable on most machines, with some models achieving up to 1/4 inch of material removal in one pass. More sophisticated models have self-leveling scarifying heads that automatically adjust to contours in the floor. As with grinders, scarifiers are available with a choice of power options (including gas, electric, diesel and air) and with hookups for attaching a vacuum to collect dust and debris. The cutting wheels themselves are mounted on shafts on a removable drum. The number of cutter shafts per drum varies by model, but generally machines with more shafts can hold more cutters per loading for increased scarifying action and faster production rates. Look for machines with quick-change drum designs that allow you to switch or replace cutters in minutes. Typical applications A variety of interchangeable cutting wheels and drum setups allow scarifiers to perform a broad range of profiling tasks. Applications include removing coatings (even heavy floor tile mastics and rubbery elastomeric or epoxy materials), light or heavy milling, grooving walkways to make them slip resistant, removing trip hazards in sidewalks, and leveling misaligned concrete joints and uneven surfaces. Attachment options Most cutters are made of tungsten carbide or hardened steel and come in a myriad of styles to suit different applications. You can choose from different diameters and widths, number of cutting teeth, and tip styles (blunt or flat for aggressive removal, sharp for gentler scarifying action, or angled for scraping). Different grades of cutters are also available, with ultra-premium grades providing a much longer service life and more predictable finish. Manufacturers can recommend the cutter style and grade best suited for your needs. Tips for best results
RENTING VS. BUYING The price tag for high-performance surface prep equipment can be pretty steep. Expect to pay about $2,000 to $4,000 for a single-head floor grinder to over $6,000 for a four-head machine. A walk-behind shotblaster with a 13-inch blast path can set you back more than $20,000 while a ride-on scarifier with a 12-inch cutting swath can top $30,000. And these prices don't account for attachments, accessories or separate dust-control equipment. If you do a lot of surface prep work, you can often justify the cost of purchasing your own equipment. But if you expect to use the machinery only about four or five times a year, you may be better off renting the equipment or subcontracting the work. For example, you can rent a 10-inch walk-behind floor grinder from GrindAll—a distributor of concrete surface preparation equipment—for about $250 a day vs. shelling out nearly $4,000 to buy the machine new. You'll also save on maintenance expenses and depreciation costs. If you do decide to buy, get the most from your investment by purchasing a machine that can perform multiple functions. It's also good to start out small, because regardless of the size of the slab, you'll always need a machine that can work in corners, next to walls and other tight spots. TEN FACTORS TO CONSIDER WHEN SELECTING EQUIPMENT
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