- The surface must be dry and in sound condition.
- Remove mildew, oil, dust, dirt, loose rust, peeling paint or other contamination to ensure good adhesion.
- No exterior painting should be done immediately after a rain, during foggy weather, when rain is predicted, or when the temperature is below 50°F – unless the coating indicates it can be used down to 35°F. Most coatings are now formulated for low temperature use.
For proper bonding of concrete overlays and coatings, it’s important to give surface the correct concrete surface profile, or CSP. To help contractors make this assessment, the International Concrete Repair Institute has developed benchmark guidelines for CSP-a measure of the average distance from the peaks of the surface to the valleys. They range from CSP 1 (nearly flat) to CSP 9 (very rough). As a general rule, the thicker the overlay or topping, the more aggressive the profile needs to be. A skim coat, for example, may require a light CSP of 2 to 4. For thicker self-leveling or polymer overlays, acceptable profiles generally range from CSP 4 to 6. Achieving surface profiles in the higher ranges often requires roughening by shotblasting or scarifying.
The following guides will help assure maximum performance of the coating system and satisfactory coating adhesion to concrete:
- Cure – Concrete must be cured prior to coating application. Cured is defined as concrete poured and aged at a material temperature of at least 75°F for at least 30 days. The pH of the surface should be between 6 and 9.
- Moisture – (Reference ASTM D4263) Concrete must be free of moisture as much as possible (moisture seldom drops below 15% in concrete). Test for moisture or dampness by taping the 4 edges of an 18 inch by 18 inch plastic sheet (4 mils thick) on the bare surface (an asphalt tile or other moisture impervious material will also do), sealing all of the edges. After a minimum of 16 hours, inspect for moisture, discoloration, or condensation on the concrete or the underside of the plastic. If moisture is present, the source must be located and the cause corrected prior to painting.
- Temperature – Air, surface and material temperature must be at least 50°F (10°C) during the application and until the coating is cured.
- Contamination – Remove all grease, dirt, loose paint, oil, tar, glaze, laitance, efflorescence, loose mortar, and cement by the recommendations A, B, C, or D, listed below.
- Imperfection may require filling with a material compatible with Sherwin-Williams coatings.
- Concrete Treatment – Hardeners, sealers, form release agents, curing compounds, and other concrete treatments must be compatible with the coatings, or be removed.
Wood – Exterior
- Wood must be clean and dry.
- Prime and paint as soon as possible. Knots and pitch streaks must be scraped, sanded, and spot primed before a full priming coat is applied.
- Patch all nail holes and imperfections with a wood filler or putty and sand smooth.
- Caulk should be applied after priming.
Wood – Interior
- All finishing lumber and flooring must be stored in dry, warm rooms to prevent absorption of moisture, shrinkage, and roughening of the wood.
- All surfaces must be sanded smooth, with the grain, never across it.
- Surface blemishes must be corrected and the area cleaned of dust before coating.
Previously Coated Surfaces
- Maintenance painting will frequently not permit or require complete removal of all old coatings prior to repainting. However, all surface contamination such as oil, grease, loose paint, mill scale, dirt, foreign matter, rust, mold, mildew, mortar, efflorescence, and sealers must be removed to assure sound bonding to the tightly adhering old paint.
- Glossy surfaces of old paint films must be clean and dull before repainting. Thorough washing with an abrasive cleanser will clean and dull in one operation, or, wash thoroughly and dull by sanding.
- Spot prime any bare areas with an appropriate primer.
- Recognize that any surface preparation short of total removal of the old coating may compromise the service length of the system. Check for compatibility by applying a test patch of the recommended coating system, covering at least 2 to 3 square feet. Allow surface to dry one week before testing adhesion per ASTM D3359. If the coating system is incompatible, complete removal is required (per ASTM 4259, see Concrete, S-W 5, “Blast Cleaning” above).