Preparing contaminated concrete for further treatment or coating is a critical step in ensuring the durability and effectiveness of the applied materials. Various mechanical methods are employed to achieve the necessary surface cleanliness and profile, each suited to different types and extents of contamination. This blog post explores six primary techniques: shot blasting, grinding, abrasive blasting, scarifying, scabbling, and waterjetting. By understanding the specific applications and advantages of each method, professionals can select the most appropriate approach for their concrete preparation needs, ensuring optimal results for subsequent coatings and treatments.
- Shot Blasting
Shot blasting propels steel onto a surface to roughen it and remove coating and contaminants. Whether handheld or walk-behind, the blasting equipment includes an enclosed blast chamber that recovers and separates dust and reusable steel shot. Because the abrasive and pulverized concrete are recovered, the system creates only very low levels of airborne dust and debris. Shot blasting can remove embedded dirt, laitance, curing compounds, sealers, and conventional coatings up to 10 mils thick, tile mastics, and brittle coatings up to 1/16 in. thick. Shot blasting is the preferred method for preparing concrete decks.
- Grinding
Grinding is performed with hand-held or walk-behind machines that rotate abrading stones or discs under pressure at right angles to the concrete surface. The purpose of grinding is typically to remove coatings less than 6 mils in thickness, mineral deposits, and slight protrusions on a concrete surface. Excessive grinding can smooth out a surface. If the needed surface profile is lost, other preparation methods must be used along with grinding Portable, hand-held grinders can be used on horizontal as well as vertical surfaces. Larger, walk-behind grinders are best suited to horizontal surfaces.
- Abrasive Blasting
Air abrasive blasting with conventional media such as silica sand or slag is used to create a light profile on concrete or, when used more aggressively, to perform deep cleaning and profiling. Rigid coatings that are 4 to 10 mils thick and some surface contaminants can also be removed by abrasive blasting. Air abrasive blasting is conducted with hoses and nozzles attached to blast pots, air compressors, and oil and moisture separators. Abrasive blasting can produce profiles suitable for applying protective sealers, coatings and concrete or epoxy toppings ranging from 20 mils to 250 mils. Abrasive blasting on concrete typically produces a large amount of airborne dust from the fractured abrasive and fractured concrete.
- Scarifying
Scarifying is performed with a rotary impact tool made of cutters (toothed washers) assembled on tempered steel rods. The rods are attached to a drum. The tool is held at a right angle to the concrete surface. When the drum rotates, the cutters strike the surface, fracturing or pulverizing the concrete. Units range from small, hand-held tools suitable for vertical and overhead application to larger, walk-behind units for horizontal surfaces. The method can be used to remove brittle coatings up to 1/8 in. (3 mm) thick, deteriorated or contaminated concrete from 1/8 to 3/4 in. (3 to 19 mm), high spots to smooth out surfaces, and adhesives. The method can also be used to profile concrete surfaces so that they can receive coatings above 40 mils in thickness, selfleveling systems, broadcast systems, or thin overlays. Surfaces grinding or the installation of an epoxy or concrete overlay would be necessary prior to application of the Pecora Deck Coating.
- Scabbling
Scabblers are used to remove coatings or contaminated concrete by chipping the concrete with piston-driven cutting heads placed at a right angle to the surface. Compressed air drives the heads. Large walk-behind scabblers are used for decks and other horizontal surfaces. Brittle coatings up to 1/4 in. thick and concrete up to 3/4 in. thick be removed by scabbling. Scabbling can also be used to create deep profiles on concrete surfaces, such as would be required to apply concrete or epoxy overlays of 1/8 in. or greater thickness. Scabbling is not appropriate for removing gummy or rubbery materials, such as elastomeric coatings, and this method is likely to produce microcracking in the concrete. The installation of a concrete or epoxy topping would be necessary prior to applying the Pecora Deck Coating System.
- Waterjetting
Waterjetting can be used in pressures varying from 5,000 to 45, 000 psi to remove water soluble contaminants, laitance, efflorescence, weak or deteriorated concrete down to 3/4 in. in depth and coatings up to 10 mils in thickness. Waterjetting is generally used outside and in areas that can tolerate mists, loud noise, and deep puddling. Surfaces which are cleaned by waterjetting will need the application of an extra base coat prior to the application of Pecora Deck Coating System.
In conclusion, selecting the right mechanical method for preparing contaminated concrete is essential for achieving the desired surface profile and ensuring the longevity of subsequent treatments. Shot blasting, grinding, abrasive blasting, scarifying, scabbling, and waterjetting each offer unique benefits tailored to specific types of contaminants and surface conditions. By carefully evaluating the requirements of the project and the characteristics of each method, professionals can effectively prepare concrete surfaces, leading to enhanced performance and durability of the applied coatings and treatments. Proper surface preparation not only extends the life of the coatings but also contributes to the overall success and reliability of the construction or renovation project. For more information, please visit our website at www.pecora.com
