Procedure No. AT 101 – MP Original Issue Date: September 7, 1990 PROCEDURE – METAL PREPARATION The adherence of any coating to a metal substrate is primarily a function of surface preparation. If the surface is properly prepared and free from contaminants one can apply a coating with the confidence that it will adhere and give many years of service life. Paying very close attention to preparation is an absolute must. ALUMINIUM SURFACES (Bare, either stripped or new) 1. The bare surface must be thoroughly cleaned and any corrosion removed. First the surface can be cleaned with naptha, acetone or MEK. If stripped metal, all stripper must be removed. 2.
Wet abrade aluminum surface with a commercial phosphoric acid etch/brightener i.e. Air Tech Alumiprep keeping surface wet 3 – 5 minutes. Rinse with clean water; water must sheet over the entire surface, a water break free surface must be had. Abrasives containing iron i.e., steel wool are prohibited for cleaning operations as particles may become imbedded in aluminum and be the beginning of corrosion. 3. Apply a chromic acid conversation coating (Alodine) to the surface. Keep surface wet for 5 minutes. Reapply several times to obtain a pale gold or tan color. Rinse thoroughly and air dry. The next primer coat must be then applied within 24 hours!. 4.
For severe service such as water immersion or use in situations where high chemical resistance is required the use of a phosphoric acid wash primer is recommended. The next primer coat must be applied within 24 hours!. 5. After the conversion coating and /or wash primer application the surface must be coated with Air Tech’s two component epoxy primer. STEEL: 1. Surfaces must be cleaned with naptha, acetone, or MEK to remove oil or other contaminants. 2. Any rust or corrosion must be removed by sanding, steel wool or steel wire brush. 3. Surface must be cleaned by wet abrading it with a phosphoric acid etch solution. Surface must be kept wet for 5 minutes minimum. 4.
Within 5 hours after surface has been cleaned it must be coated with an Air Tech two component epoxy primer. Note: Wash or self etching primer is an optional treatment for steel surfaces after acid etch. It must be used on surfaces which will be placed in extreme service ie. long term water immersion etc. It is very good for zinc coated surfaces (galvanized).