How to Work With Automotive Spray Primer

There are a couple of types of commonly used automotive spray primers which may be applied during body work and finishing process.

There is "Finish or Final" primer and also a "High Build" formula. The finish primer is generally used for metal that already has a smooth finish or it may be applied over the high build primer for a smoother finish.

The High Build primer is generally used when the metal is a bit rough and you need a slight building to help cover scratches or pinholes.

Application is the same with the exception of the High Build needing more drying time between coats and before sanding.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Spray Primer in the can, (High Build or Finish Formula)
• Various grades of sandpaper ( 60-120-320-and 600 will cover all possible needs)
• Clean cotton cloth or painters tack rag
• Paper face mask or respirator
• Hand sanding block
• Common hair dryer (Optional, to speed up drying time)

1. 
   Various Grades Of Sandpaper

   Sand off surface waxes and sand down surface paint along with any bumps using 60 grit or 120 grit sand paper. If you use 60 grit which will get you deeper under existing paint and remove debris and bumps you should follow up with 120 grit to sand down scratches left by the harsh 60 grit paper with your goal being to end up with a dull smooth surface oil and wax free with the paint being dulled.

2. Use your cloth or tack rag to remove all sanding dust and be sure any corners or crevices are dust free or when you begin to spray particles may blow up into your finish. If you happen to have a compressor with an air blower attachment, this is ideal. Wash off the work with clean water and be sure the surface is completely dry.

3. Be sure you have proper lighting set up and you are in a properly ventilated area with no direct drafts aimed at your work area.

4. 
   Finishing and High Build Primer

   Shake the can allowing the rattler to mix the paint thoroughly, put on your face mask and with the nozzle of the can approx. 8 inches from the surface to be sprayed begin spraying a light surface coat. There are two common methods of spraying. One is holding the nozzle down at all times keeping the can moving and the other is to shoot calculated shots of primer onto the surface. I prefer to shoot calculated shots since the primer is less likely to run as it may when holding the nozzle down at all times releasing a constant greater volume of product.

5. 
   Face Mask on whenever spraying!

   Allow the first coat to dry before applying another. If you are using the finish primer you could usually spray again within a minute or two but if you are using the high build you should wait approx. 5 to 10 minutes between coats, possibly longer depending on the thickness of application along with humidity and heat levels. You may also use a hair dryer to speed up drying time, holding it approx. 8 to 10 inches from the wet primer keeping it moving at all times.

6. 
   High Build Primer Applied!

   You goal is to apply 2 to 3 coats of primer which needs to dry thoroughly, ideally some hours or even overnight, before the final step of fine sanding the primer.

7. 
   Typical Hand Sanding Blocks

   Using your 320 to 600 grit paper on your hand held block sander "lightly" sand the primer with your goal being to smooth down any runs and flatten out the primer finish. Use the 320 or even 120 grit for runs and bumps and 600 grit for final smoothness.
   If you sand down too far and create a bald spot a simple quick shot of fresh primer over the spot is all you will need to do followed by a very light 600 grit sanding.

8. 
   Glazing Spot Putty Compound to fill in flaws and to help feather edge..

   If there are any evident flaws, such as pinholes, at this point you can either spray over with the high build primer or work with a Glazing Spot Putty which will serve to fill in any pinholes or scratches.
   Sand the glaze down with 120-320 grit and prime the area again.

Tips & Warnings

• Be sure the surface to be primed is oil, chemical and wax free or the primer will not adhere properly.
• Don't be afraid to re sand an area if oil pops up or remaining wax is not allowing the primer to stick.
• Apply in temperature of over 50 degrees and never in direct sunlight.
• Wait until the primer is completely dry before final sanding or you may scuff and peel up the primer.
• Spray in a dust free environment, sweep up and wet down the floor first if you are working in a garage for instance.
• Always wear your face mask so as not to breathe in the primer vapors.
• Work in a ventilated area with no direct drafts aimed at your work area or yourself. An exhaust fan is always a good idea!
• Never spray primer within your home, the harmful vapors will linger for quite a while.