Proper surface preparation is critical for a successful floor coating system. The concrete must be clean, sound and free of any contaminants that may interfere with the adhesion of the coating. The level of surface preparation is dependent upon the substrate condition, service expectations, environmental conditions and coating type.
Clean and Screen Previously Painted Floors
Clean the surface with a degreasing cleaner such as Krud Kutter Heavy Duty Cleaner. Mix according to label directions and allow the cleaner to dwell for 5-10 minutes. Pressure wash the floor with a minimum of 3000 PSI to remove all dirt, grease, grit, grime and any loose or peeling paint. Flood rinse the floor to remove all of the cleaner. Let the floor dry and thoroughly screen the floor with a mechanical floor buffer with a 50-60 grit screen. Sweep or vacuum the dust & debris from the floor. The profile of the floor must be equal to or rougher than 120 grit sandpaper prior to applying any coating.
Concrete Surface Profile
International Concrete Repair Institute (ICRI) created the concrete surface profiles (CSP) classifications provide visual standards for the purpose of specification, application and verification of surface preparation. There are ten classifications (CSP 1-10) of surface textures based on the average distance from the peaks of the surface to the valleys. They are accepted industry standards to help guide the installer achieve the proper texture for successful bonding of the overlay or coating. The lower number profiles are smoother (CSP 1 is nearly flat), and the higher numbers have more “tooth” and get progressively rougher. The CSP is determined by the project requirements and type of coating system.
Eye protection, gloves and a respirator will be required for this procedure. Apply muriatic acid diluted 4-1 with water; ALWAYS ADD ACID TO WATER. Allow the acid to bubble and fizz, occasionally “stirring” with a whisk push broom. Allow to dwell up to 15 minutes while it continues to bubble and fizz. Do not allow the floor to dry, add more acid solution if necessary to keep wet. Neutralize with baking soda mixed 1 cup to 1 Gal of water, sprinkle evenly across floor and allow to dwell for a minimum of 10 minutes. Thoroughly rinse the area with clean water with a garden hose at low pressure. Remove any contaminates from surface to be coated with pressure washing, minimum 2400 PSI. When the preparation is complete, the profile of the floor must be equal to or rougher than 120 grit sandpaper. The pH of the concrete must be in the 6-9 range before any coating is to be applied. Only for uncoated and unsealed concrete. Acid Etching can reach a CSP of 1.
Diamond grinding is a concrete surface preparation technique that corrects irregularities such as minor pits and divots, faulting and roughness on concrete pavements. This is achieved by using diamond bits to grind the surface. This also leaves a very smooth profile-ideal for thin-mil coating or sealer applications. Diamond grinding also profiles the concrete and can remove existing coatings and contaminants from the surface. Grinding can reach a CSP of 1-2 and can leave circular patterns or gouges in the concrete.
Shot blasting is a preferred method for preparing concrete for coating. A shot blaster propels steel shot at the ground over and over again at high speed. The impacts of the shot pulverize concrete and previous non-elastomeric coatings and roughen the surface. The recommended blast profile will depend upon the coating system specification, but generally will range from 2.0 – 10 mils in depth (CSP 2-3). After track blasting, sweep / vacuum all dust, dirt and debris from the area to be painted.
A scarifier consists of rows of toothed washers assembled on steel rods that are mounted to a rotating steel drum. As the drum spins, the washers strike the surface, fracturing and pulverizing concrete, and producing a striated pattern. Scarifying only works on horizontal surfaces. Scarifying will create a CSP of 4 to 7 and will require a high build coating system or concrete overlay system.
ASTM D4263 – Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method – This qualitative method will indicate the presence of moisture movement, but it will not quantify the amount of moisture movement, and is only useful in determining that additional testing is required.
ASTM F1869 – Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Sub-floor Using Anhydrous Calcium Chloride. To determine the amount of moisture movement, the floor and surrounding environment must be in the anticipated service condition. The test must be conducted over raw exposed concrete, which has been exposed to the environment for at least 24 hours. A quantitative evaluation is conducted wherein the anhydrous calcium chloride container & contents are pre-weighed on a gram scale, allowed to remain in it’s container with the lid removed, and the container placed under a sealed dome to prevent loss of moisture for a period of 60 to 72 hours. Three tests are required for the first 1000 S.F., with one additional test for every 1000 S.F., or fraction thereafter. The container is removed and again weighed on a gram scale to determine the weight gain of the anhydrous calcium chloride. A calculation is performed to determine the amount of moisture absorbed. These results are quantified as the rate of moisture vapor transmission expressed as pounds per 1000 square feet of surface area per 24 hours. General Polymers has adopted a commonly accepted value for application of polymer coatings or toppings to be not more than 3 pounds of moisture per 1,000 square feet per 24 hrs.
Upon completion of the surface preparation, any undesirable surface imperfections: cracks, chips, divots, bug-holes, protrusions, ridges, penetrations, mortar splatter or sharp projections must be repaired. Any protrusions shall be ground down or knocked off with a chisel or other tool.
Cracks: All cracks should be v-cut to remove all loose or deteriorated concrete and provide a uniform substrate to caulk or patch.
Divots, bug-holes and non-moving cracks: greater in depth than the coating system and less than 1/4” should be filled with Florida Paints DuraDek FP6060 Concrete Overlay, Florida Paints DuraDek FP6062 Stamp Mix or an epoxy slurry; allowed to dry and cure and sanded/ground to desired smoothness. For depths greater than 1/4” apply multiple applications of the DuraDek products or hydraulic cement in accordance with the manufacturer’s instructions. Control & Expansion Joints: any joint that will experience movement of any kind from heavy equipment must be repaired with an approved flexible joint sealant to prevent damage to the joint and the floor coating.
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