Paint surface preparation

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Treat any rusty metal with a metal conditioner such as "Metalprep," "Deoxidine," etc. Wash with water, dry thoroughly, immediately spot spray bare and feathered areas with primer-surfacer and then sand smooth. Rub edges of patches with rubbing compound to remove scratches in old finish, and overspray.

Then spray over area to be patched one medium coat of Pyra-Prep or equivalent, reduced 1 part Pyra-Prep with up to 1 1/2 parts thinner. Allow to dry at least thirty minutes to secure maximum sealing. If necessary, scuff lightly to remove nibs.

Metal treatment

All metallic surfaces should be carefully cleansed with solvent such as cleaners' naphtha to remove any grease, oil, or other foreign matter that might be present. In some instances, as noted in the following discussion, it is desirable to thoroughly treat the surface with metal conditioner.

1. Uncoated Body Steel.—It is strongly recommended that uncoated body steel be sanded before priming, preferably with a metal conditioner such as "Deoxidine," "Metalprep," etc. When steel is prepared for priming, the primer should be applied at once. Do not let the metal stand without primer, as rusting starts immediately, causing poor adhesion.
   
2. Zinc Coated Metals.—There are numerous zinc coated metals on the market ranging from untreated Spangled Galvanized Iron (hot dipped) to the phosphate coated electrolytically deposited zinc sheets. The adhesion retention and durability of finishing systems over these metals will range from poor to good depending upon the particular metal involved. The following groups or classifications list the precautions, special treatments required, or specific finish systems necessary to give best results.
   
   As a rule, these metals should not be sanded or treated with acid type cleaners since they will remove either the phosphate coating if present or, in the case of electrolytic sheets, the thin coating of zinc.
   
   a. Spangled Galvanized Iron.—Experience shows that this metal is one of the most difficult metals to finish in order to secure satisfactory adhesion. Although sanding with fine sandpaper and cleaners' naphtha sometimes improves adhesion, very inconsistent results may occur.
   
   Finishes of satisfactory adhesion immediately after application may become very brittle after several months' aging. The recommended system for finishing this type of metal is first remove grease, dirt, and other foreign matter with cleaners' naphtha and apply one light coat of 67-747 Spangled Galvanized Iron Primer. Allow to dry at least eighteen hours and follow with surfacing coats of Preparakote.
   
   b. Treated Spangled Galvanized Iron.—Sheets such as "Paint Grip," "Zinc Grip-Paint Grip," etc., are phosphate coated at the time of manufacture. These sheets normally do not require any special treatment other than removal of grease, dirt, or other foreign matter. If the surface is mechanically abraded or the phosphate coating removed by spot welding, etc., it is advisable to treat the sheet with one of the metal conditioners such as "Lithoform No. 2," or "Galvaprep." Apply one light coat of 67-747 Spangled Galvanized Iron Primer. Allow to dry at least 18 hours and follow with surfacing coats of Preparakote.
   
   c. Galvanneal.—This is a specially processed galvanized iron to give improved adhesion. No special treatment is required other than the use of cleaners' naphtha to insure a clean surface. Prime and surface with Preparakote.
   
   d. Non-Spangled Galvanized Iron.—Representative of this group are the electrolytically zinc coated sheets which are generally phosphate treated at the mill, such as "Paint Lok," "Cold-rolled Paint Grip," and "Weirzin." Some variations in adhesion to these surfaces have been noticed and treatment with "Lithoform No. 2" or "Galvaprep" may be used to obtain uniform results. Preparakote is recommended as a primer and surfacer for these metals.
   
3. Aluminium.—Wash with cleaners' naphtha and treat with a metal conditioner such as "Alumi-prep," "Alodine," or "Deoxidine." Do not sand. In building truck bodies of aluminium it has been found desirable to prevent corrosion on the inside of the sheets by spraying a coat of 63-111 Zinc Chromate Primer, permitting hard dry before assembly to prevent a rapid corrosion resulting from electrolysis. Prime and surface outside of sheets with a minimum of two spray coats of Preparakote.
   
4. "Dowmetal."—This metal is a magnesium alloy, manufactured by the Dow Chemical Co. During manufacture it is given a chrome-pickle treatment which is necessary to secure adhesion of the finish. Where the chrome-pickle layer has been removed by sanding or damaged in any way, it is imperative that the metal be sanded and then well brushed with a generous amount of chrome-pickle solution freshly prepared in accordance with the formula given below.
   
   Aluminium, glass, or earthenware containers may be used and the solution may be applied with an old but clean paint brush. It is advisable for the operator to wear rubber gloves. Sodium Bichromate (Na2Cr207.2H20) 1.5 lbs., Concentrated Nitric Acid (Sp Gr 1.42) 1.5 lbs., Water to make 1.0 gal.
   
   The solution should be well worked into the metal and should be allowed to remain in contact for at least 1 minute. The residual solution must be washed off with water. Do not allow solution to become trapped in joints, etc. When the metal is dry, prime and surface with Preparakote.
   
5. Stainless Steel.—Dry sand thoroughly with No. 280 paper and wash with cleaners' naphtha. Prime and surface with Preparakote.