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Surface Preparation & Application Guide
Next to the proper selection of a coating system, surface preparation is the most important procedure in the use of industrial coatings. Although, many of the coatings listed on this site are “surface tolerant, moisture insensitive or underwater coatings”, the overriding factor is that the better the surface preparation, the better and longer lasting the performance.
The following methods have been established by the Steel Structures Painting Council, and others, as levels of cleanliness prior to coating:
- SSPC-SP 1. Solvent Cleaning — Removal of oil, grease, dirt, soil, salts, and contaminants by cleaning with solvent, vapor, alkali emulsion or steam.
- SSPC-SP 2. Hand Tool Cleaning — Removal of loose rust, loose mill scale, and loose paint to degree specified, by hand chipping, scraping, sanding, and wire brushing.
- SSPC-SP 3. Power Tool Cleaning — Removal of loose rust, loose mill scale, and loose paint to degree specified, by power tool chipping, descaling, sanding, wire brushing and grinding.
- SSPC-SP 5. White Metal Blast (NACE 1,SA 3) — removal of all visible rust, mill scale, paint, and foreign matter by blast cleaning with sand, grit or shot.
- SSPC-SP 6. Commercial Blast (NACE 3, SA 2) — Grit blasting to a high, but not perfect degree of cleanliness. Blast cleaning until two-thirds of the surface area is free of all visible residue.
- SSPC-SP 7. Brush Off Blast (NACE 4) — Blast cleaning of all except tightly adhering residues of mill scale, rust and coatings, exposing numerous evenly distributed flecks of underlying material.
- SSPC-SP 8. Pickling (Acid Etching) — Complete removal of rust and mill scale using sulfuric, hydrochloric or phosphoric acids, followed by a water wash to remove any residue. Can also be used in diluted form for preparing concrete.
- SSPC-SP 10. Near White Blast (NACE 2, SA 21/2) — Blast cleaning to White Metal Cleanliness, until 95% of the surface is free of all visible residues.
- SSPC-SP 11. Power Tool Cleaning to Bare Metal — Power tool cleaning to obtain bare metal surface and to produce or retain a profile. This procedure goes beyond SSPC-SP 3 in that it requires complete removal of all visible traces of oil, dirt, grease, rust, mill scale, paint or other corrosion products and foreign matter. If the original surface is pitted, slight residues of rust and paint may be left in lower portions of the pits. If the surface needs to be roughened, the profile produced shall not be less than one mil in depth and suitable for the material selected
In conjunction with surface cleanliness is surface profile, which is defined as the measurement of roughness which results from blast cleaning. The profile depth is a measurement from the lowest valleys to the tops of the highest peaks. The profile depth is dependent on the size, type and hardness of the blast media selected, as well as the velocity, pressure and hardness of the surface. In general, for thin film coatings up to 30 mils/coat, a profile depth of at least 3 mils is required. For thicker trowel grade materials a profile depth of at least 4 mils is required.
Proper mixing is essential for achieving a consistent and uniform coating. The following procedures will help insure proper mixing:
- Pour the two components into a clean container of ample size to properly mix the materials without spilling. Use care to insure that all of the material is removed from each container.
- Mix the materials until a consistent, uniform and streak free consistency is obtained by the use of a paddle, spatula or power mixer.
- Pour this mix into another clean or original container (if applicable), scraping all of the mixed material into this container and re-mix.
- Repeat the above procedure 2-3 times before using.
In general, once the surface has been properly prepared, it should be checked to insure that it is free from moisture, above the minimum application temperature for the material and that the surface is at least 5°F (3°C) above the dew point. Coating can then proceed by airless spray, rolling, brushing, or trowel as specified for the product
When applying more than one coat, it is extremely important that overcoat windows are followed. In addition, the surface should also be checked for moisture, dust, dirt or other contamination as well as for amine blush.
Although most Duromar® materials are resistant to amine blush, anytime you have high humidity or low temperatures, this phenomena may occur. Amine blush is evidenced by a glossy and somewhat greasy exudate on the surface, which may dry to a chalky white color. It is easily removed by using a 2% solution of hydrochloric acid or MEK.
Force cures are recommended for severe service conditions as both physical and chemical properties are enhanced. It can also be used to reduce the time to “full cure.” A general guideline of 4 hours at 180°F (80°C) will completely cure any of the Duromar® products. Force cure should not start until material has firmly set.
For a complete guide to the use and application of our 100% solids, zero VOC materials, please contact us.