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The recommendations given
here are based on experience of the du Pont organization in the
fifties. Trade names used refer mostly to du Pont products. Other
organizations, naturally, offer materials to do the same job under
different names. Your nearest
automotive jobber can acquaint you with the various kinds of refinishing
material on the market.
One word of caution, however : In general
don't mix brands. Though two brands of material may be of comparable
quality they may not "get along" with each other. This
is especially true of the finishes and their thinners.
Before any sanding is done in connection
with touching up of passenger cars, wipe surface to be painted with
a clean cloth soaked with benzene or commercial solvent to remove
all traces of wax, polish, and grease. Cut down the edges of broken
spots with coarse sandpaper or with lacquer-removing solvent if
the old finish is lacquer, and feather the edges with 400 paper.
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.
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.
- 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.
- 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.
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.
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
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
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.
- Stainless Steel.—Dry
sand thoroughly with No. 280 paper and wash with cleaners' naphtha.
Prime and surface with Preparakote.