What is shotblasting and how it works.
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.
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.
Surface preparation is considered to be the most
important step of any resinous flooring application. Improper surface
preparation could turn what seems to be a simple process into a lengthy,
difficult repair. The following conditions will dictate the type of surface
Proper jointing will minimize cracking which could transmit through the
resinous flooring system.2. Elevated Slabs
a. Pan construction should be vented.
b. Metal deck construction should be properly jointed to minimize cracking.B.
Curing and Finishing Techniques1. Curing compounds, if used, must be mechanically removed prior to resinous flooring installation.C. Age of Concrete
Concrete must be a minimum of 30 days old for resinous flooring applications. Primers are now available which can be used on fresh (green) concrete on some installations.D. Previous Contamination can affect the bond of the resinous flooring and must be removed. Types of contamination are:1. Oil, grease, or food fats can usually be burned off with a flame gun or removed with a commercial degreasing compound. 2. Curing compounds, sealers, and other laitance are best removed mechanically with:
- vacuum shot-blasting
- Diamond grinding
E. Present Condition1. Test for moisture: Coating system bond failures on slabs on grade and elevated/lightweight concrete caused by moisture vapor transmission are the industry's largest single problem and result in extreme frustration from owners, clients, and contractors. Floorshield will test for moisture vapor transmission upon request from owner. The recognized methods are:
2. Moisture related failures can be prevented through:
- ASTM-F-1869 Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride: The maximum allowed water/vapor transmission rate is 3 pounds per 1,000 square feet per 24 hours.
- ASTM F-2170 Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes: This test measures the relative humidity in the slab below the surface. If taken over a period of time, it will show the rate of drying in the slab. The maximum relative humidity should be below 80%.
3. A clean surface is necessary to establish a strong bond between the resinous flooring and concrete.4. Resinous flooring systems are only as sound as the concrete they are applied to. All unsound concrete should be repaired or replaced prior to resinous flooring applications. 5. Resinous flooring materials should be applied to level concrete substrates. Grind or fill high and low spots prior to application.6. Repair cracks prior to resinous flooring applications.F. Mechanical Prep vs. Acid Etching
- A. Placing new concrete over an efficient vapor barrier.
- B. Testing for moisture vapor transmission as prescribed above prior to resinous flooring application.
- C. Applying a moisture vapor transmission reduction system where moisture content is too high for successful resinous flooring applications.
Resinous flooring materials ideally bond to concrete with a rough, sand-paper finish. This finish can be achieved by either acid etching or mechanical methods. The choice of preparation is dictated by the factors above. Floorshield prefers to mechanically prep our floors prior to any resinous flooring installation.H. Mechanical Preparation
Contamination and other foreign materials must be mechanically removed to ensure a satisfactory bond. All dust and debris must be thoroughly removed.II. OLD CONCRETE
Old concrete surfaces must be structurally sound. Any unsound areas must be repaired prior to proceeding with the resinous installation. Remove existing paint, scale and loose concrete by rough sanding, sandblasting, shot blasting, or grinding. Structurally sound concrete should be mechanically prepared to remove any contamination. Vacuum shot blasting is the best method for achieving a good profile for bonding and should be used where possible. Upon request, Floorshield can provide the following test to check moisture.
ASTM-F-1869 Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.
III. NEW CONCRETE
New concrete must be well cured and dry prior to coating. Allow to cure a minimum of 28 days unless using green concrete primer. No curing agents or sealing compounds should be used at any time prior to coating. A light steel trowel finish is recommended when finishing the concrete surface.
Any oil, grease, laitance, or other foreign material must be removed. Steam clean with a strong degreaser such as tri-sodium phosphate. Laitance and other foreign material are best removed by mechanical methods such as vacuum blasting, scarification, or grinding.
All new concrete can be acid etched or mechanically prepared by vacuum shotblasting, sand blasting, scarifying, or grinding. Vacuum shot-blasting provides the cleanest environmentally safe area during cleaning. It also provides a mechanically rough surface to achieve a good bond.