Golden rules for preparing the surface before painting

Whether it is a bodywork painting or a building painting, painters know it well: the secret of a successful painting is the preparation of the support. Indeed, even if painting 2 coats of paint is done in less than 5 minutes, it is 10 times more time that will have been spent preparing the bodywork. Following these few rules will save you a lot of worries!

Bodywork preparation is the basis of the rules of the art of painting:

1/ Avoid reactions and paint defects in the bodywork

If you paint on a surface that is not "sound", this will create a visible defect (dots, bubbles, etc.), or a lack of adhesion, or even a "refusal": In order to avoid any surprises, you must not paint or prime on:

• dusty or dirty surface
• a surface where there is presence of humidity, or greasy residue (fingerprints for example), or glue, or silicones
• presence of rust, or unstable bottoms.

The bottom must therefore be dried, degreased using a degreaser, and dusted using sticky pads.

2 / Primers:

First identify and assess the medium:

Is the surface already painted?
> In this case, sanding is mandatory to create the adhesion. It is done dry or wet*, with the grain recommended on the technical sheet of the paint that will be applied. By hand on curved surfaces, with a sanding block on flat surfaces.

For sanding difficult areas, you can use a sanding sponge

* Wet sanding allows for better sanding without heating or clogging

Caution: you will need to make sure that this old painted background is of good quality, that it does not flake, and that it is compatible with the paint that you are going to apply on top. If in doubt, scrape, sand and apply a primer.

Is the support raw/bare*?
a raw substrate is a bare material, for example, a body stripped or sanded down to the base: sheet metal
In general, all raw materials should not be painted without first being primed.
> glass, concrete, iron, aluminum, chrome, glass, plastics

Ensure good adhesion with an adhesion primer:

What is the type of metal, type of plastic, or material?

It is important to apply an adhesion primer that matches the material, to ensure that the paint will not peel off after a month!

You cannot use an anti-corrosion primer for iron and steel on aluminum or other non-ferrous metal.

Applying a primer alone does not guarantee that the paint will stick!

For example, if you apply an adhesion primer for plastic on plastic without having also done any preparation, the adhesion will be close to 0.

On plastics, you must carry out various preparation phases (flammable, sanding with a sponge, removing static electricity, degreasing), on metals you must deoxidize (remove rust by sanding) and degrease, on non-ferrous metals or even concrete, you must sometimes remove the rust with an acid solution.

The bottom must be smooth and perfect, and free from imperfections.

On painted surfaces in good condition, light sanding with a fine-grain abrasive (P800) is sufficient.
On scratched or damaged surfaces, you will need to fill with putty and surface fine defects with a primer (filler or surfacer primer in French), then sand with abrasive paper (P320 or 400)

Checking:
- by eye, to check for any defects
- with the bare hand, to feel if the surface has an imperfection


Degreasing:
Using a degreaser removes glue residues, or invisible greasy traces. This must be done with a damp cloth, and this degreaser must be immediately removed with another dry cloth, before it evaporates, because it contaminates the surface.

Just before painting:

The surface is perfect and clean, primed, sanded...
The final step before starting to paint the bodywork is a final dusting using a sticky pad, without pressing, and a little pressurized air.

Accessories:
The sanding case 

The preparation kit

Complete paint kits
Varnishes and finishes
Complementary products for bodywork paint
Types of bodywork paints
Primers or bodywork primers
Epoxy paint for rims
How to repair scratches on bodywork paint?
How to repaint your bodywork in matt or satin