Why must I sand down the car to bare metal before painting?


Paint is perhaps one of the most difficult DIY projects for the typical enthusiast who isn’t afraid to get their hands filthy when working on their own automobile. You either do it well or it looks bad, which is why so few people want to be hands-on and instead take their job to a shop. Yet with a little time, a lot of patience, and a few techniques of the trade, even a beginner can prep and paint an automobile like an expert.

Things You’ll Need to Prep and Paint Your Car:

  • Air compressor
  • Paint sprayer (HVLP, LVLP, or airless)
  • Orbital sander with multiple-grade sanding pads
  • Hand sandpaper with grades ranging from 120 to 800 for prep and finishing sanding
  • Surface cleaning solvents (acetone/Eastwood Pre)
  • Masking tape and paper
  • Body filler for repairs
  • Primer
  • Basecoat paint
  • Clearcoat
  • Paint thinner and catalyst or hardener
  • Respirator, eye protection

How to Prep Your Car to be Painted

  1. Sand the paint down to bare metal, the original primer, or just enough to let the fresh paint to adhere. Dry sand using 180-grit sandpaper to remove rust or surface damage before moving on to a 320-grit paper to remove your previous 180-grit scratches. Whichever method that you decide, follow it up using 400- to 600-grit sandpaper to sand the paint to prep the existing paint surface for the new coatings to be applied.
  2. It is up to you how much you sand, but for the best results, remove the paint down to bare metal, re-prime the surface with an automotive primer, and then apply your final paint.
  3. When painting an automobile or components, always sand the edges exceptionally carefully. If paint is going to lose adhesion and start peeling, it will probably start from an edge of a panel that was not sanded properly.

How to do Dent Repair Your Car Prior to Painting

Minor dents and patches may be easily filled with body filler. Body filler is a plastic resin that is sandable, adheres well to metal, and lasts a long time, but more importantly can make a dent completely invisible. Eastwood’s Contour Premium Body Filler was utilized. The Contour “all-in-one” filler actually inhibits rust long after painting and offers unique self-etching properties that bite into the surface for maximum adhesion.

It just requires a tiny quantity of hardener combined with filler material. A little ribbon-sized line across your filler is recommended (size of a pea). Never beat or aerate the mixture while adding the two agents. This will cause bubbles or pinholes to appear when applied.

Wait for it to harden, and then sand it smooth. Remember that appropriate prep work is essential for a successful paintjob.

Before to applying primer, use Bondo glazing and spot putty to fill any pinholes or tiny defects.

To remove silicone, wax, shine, grease, and grime that might otherwise contaminate the painted surface, Eastwood’s PRE Paint Prep cleaner was employed.

Our primer, basecoat, and clearcoat were applied using an Eastwood Concours HVLP paint gun. Eastwood sells paint guns made by Eastwood, DeVilbiss, Binks, and others. Prior to painting, an Eastwood electronic air pressure regulator and moisture filter were added.

How to Properly Prime Your Car Before Painting

Prime any surface where you used body filler to fill scratches or pits left in the preparation process. The primer can fill up sand scratches from 180 to 320 grit.

Always stir your paint, never shake it. Notice the pinholes caused from bubbling primer on the test below, which came from a can that was shaken.

Smooth paint lines or drips smooth to the surface using 600-grit wet/dry paper, taking careful not to sand too much and expose the metal again.

How to Properly Apply Paint to Your Car

Spray the paint according per the manufacturer’s instructions. With a hardener or catalyst, automotive enamels and certain polyurethanes perform better. Make sure the paint is thinned correctly for the equipment you are using, but avoid over-thinning, which will decrease the gloss of the finished surface and can cause runs.

While pouring paint, always use a screen to prevent pollutants from entering the paint gun.

To minimize clutter and speed up cleaning, we used DeVilbliss DeKups disposable cups which only require pouring into a disposable cup, placing into a container, capping off, and attaching directly to the gun. Before to applying the basecoat, a tack cloth was utilized once again.

You may want extra tips and nozzle caps for the gun depending on the kind of paint you intend to spray. Some paint guns come with hefty priming tips and nozzle caps, while others are better suited for spraying lighter-bodied paints and clears. You’ll need a spray gun with a 1.3 to 1.5mm fluid tip for lacquers, enamels, urethanes, basecoats, and clearcoats. A spray pistol with a 1.0mm fluid tip is required for spraying water-based automobile paints. A spray cannon with a 1.8 to 2.2mm fluid tip is appropriate for heavier paints and primers. Prior to applying the final paint, we sprayed onto a sample sheet to compare colors.

On the initial application, use a flash coat. Allow the last layer of basecoat color application to properly dry before moving to the final clearcoat stage. In between applications of touch-up paint or clearcoat, do not wet sand or use prep solvent. Apply two to three coats of clearcoat using a smooth left-to-right motion while allowing 5 to 10 minutes in-between each coat, depending on the weather and activator used.

There are several varieties of clearcoats on the market now, as illustrated from right to left: U-Pol 1K single stage aerosol; Acme two-stage 2K we purchased from Automotive Paint, which requires a catalyst mixture; and Eastwood two-stage 2K aerosol clear. Because of their longevity and chemical resistance, we suggest 2K-type clearcoats.

Eastwood’s 2K Clear aerosols allow you to paint with the durability and precision of a two-component coating without the paint gun. When you click the bottom button to activate the mixing, the revolutionary nozzle and valve technology, paired with its two internal chambers, assures the proper ratio.

Clearcoat may be sanded with 1,500-grit wet sandpaper to remove small runs, dirt, and other minor imperfections. After completely dried, use Rubbing Compound to get the desired amount of shine.

We didn’t have to wet sand our clearcoat since it applied like glass. Learning to paint an automobile takes time and should not be hurried. Paint carefully and meticulously, and you’ll be rewarded with a fantastic result.

Related Questions

  • What happens if you don’t sand your car before painting?

    A flat surface will not readily accept new paint. Thus, if you don’t sand the paint job (at least a little bit), your paint will begin to flake and peel in no time at all. A little surface roughness will give the traction required to keep the paint in place.

  • Should I take the car to bare metal before painting?

    If you want to remove paint from the car’s bodywork, use 1,200-grit paper or sanding pads to remove the clearcoat and paint rapidly. To avoid the headache of trying to match the paint you want to apply to the existing paint on the car, you’ll need to remove the primer and expose the bare metal.

  • Should I sand my car to bare metal?

    Sand the paint down to bare metal, the original primer, or just enough to let the fresh paint to adhere. Dry sand using 180-grit sandpaper to remove rust or surface damage before moving on to a 320-grit paper to remove your previous 180-grit scratches.

  • Should I sand my car down to bare metal?

    For example, before you begin painting, you should repair any damage to the car’s body. This includes corrosion, dents, and other spots that need repair. Then, sand away the old paint until just the bare metal is visible.


  • https://www.motortrend.com/how-to/1307-prepping-and-painting-your-car-part-2/

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