Applying paints with spray guns

Spraying paint with a pneumatic gun consists of atomizing a mixture of air and paint using a nozzle which is the main component of guns.

The advantage of spray painting is a uniform application of the paint with a jet of air without ever touching the surface of the support, which avoids marks and speeds up drying.

All current paint guns are dual action: this means that you can use the trigger to spray air only (trigger pressure at around 10-20%) or air + paint. You can feel a click and a difference in the resistance of the trigger, between air spray and air + paint spray.

The trigger then allows you to dose the paint supply, depending on the pressure on the trigger.

Practiced both in bodywork and in construction for painting ceilings with “airless” sprayers, spraying is also used for structures, frames for example. It is a much more efficient and faster method than painting with a roller or brush and it gives an incomparably better result and finish.

The basic rules and principles of spray painting

Horizontal spraying without crossing
Unlike other methods of painting, spray painting should be done only with a movement from left to right, then from right to left. We never cross the layer horizontally and vertically with a paint gun.

The round trip gesture
Generally, to apply a layer, you go back and forth.
On the other hand, when painting a paint or varnish with a spray gun, we overlap the next coat half, when applying the coats in the direction of the bottom or the top.

► Rule No. 1: the secret of pistol practice is to have a wrist “mounted on a ball joint” which is flexible and capable of following the contours of the surface: the pistol must always be perpendicular to the surface.

► Rule #2: The gun must always be moving when spraying.

► Rule n°3: respect the 4 parameters which are speed / distance / angle / air pressure. This determines the quantity of paint or varnish that will be deposited on the support.

► Rule n°4: arriving at the end of the stroke at the edge of the part, the gun changes direction to carry out the return layer. At this point, the painter must let the air out and must stop spraying the paint for a brief moment.

The importance of rule number 4: the position of the paint gun.

The air flow or pressure

To obtain a dry film of the right thickness, with the correct color, it is necessary to have a good air/paint ratio. The technical gesture is not everything!

Air flow is related to the air pressure (bars or psi) in the pipe.
It is important to monitor the air flow (m3/h) available when painting large surfaces (such as a complete vehicle for example) and in this case, you must have a compressor of sufficient size, in order to have stable air flow and stable pressure.

It is possible to simply follow the recommendations in the technical sheet of the product you are using.
Example: 2.5-3 bars / nozzle: 1.4mm

It is recommended to use a certain nozzle size, which naturally corresponds to the viscosity and thickness of the product, and to use a certain air pressure, which is adjusted with the pressure gauge at the outlet of the compressor. 'air.
It is rather a suggestion, because the appreciation is free for the painter.

We therefore recommend using common sense and carrying out a few spray tests just before work. Depending on the size of the nozzle, the dilution of the product and also the size of the room, the painter can adjust his gun and the air pressure, in order to adjust his spray jet:

→ If the air pressure is insufficient, the deposited layer will be too thin. This can result in a paint that is too transparent or a varnish that lacks shine.

→ If the air pressure is too strong, the product will be projected too forcefully onto the surface, this increases paint loss by creating aerosols and this can create defects in the wet paint film deposited on the surface (marbling, powdering ...).

Paint the different products with a spray gun

In the field of bodywork, the art of spray painting reaches its highest level of mastery during the varnishing phases. Achieving a shiny, flawless varnish is always a delicate exercise, even for an experienced painter.

At the intermediate level, the application of paints is noticeably easier and is within the reach of almost anyone, by applying thin, repeated coats to just complete base coverage.

And finally, primer type products are not difficult to apply, because they are quite coarse filler products.

Painting water-based or solvent-based paints

Solvent paints are easier to apply than water-based paint. They are noticeably more fluid and dry more quickly.

Water-based paints are a little thicker and it is not allowed to dilute it freely, as it is possible to do with solvent-based paints. Water-based paints are sprayed with more air and as their evaporation is slower, it is necessary to increase the waiting times between coats and also to help this evaporation, in particular with air.

HVLP guns for bodywork painting

There are 2 types of guns mainly used in bodywork : these are the HPLV and HVLP guns (the latter offer an optimal ratio of transfer to the support: less consumption and loss of paint during spraying).
Today, a body gun is necessarily an HVLP. It includes a cup, a handle, a trigger, a nozzle, a needle, two to three adjustment wheels which are used to adjust the air pressure, the shape of the jet and the locking of the needle.
You are starting in painting and want to know which HVLP body paint gun to choose ? Just know that a bad painter with a high-precision spray gun will paint badly, while a good painter will do a perfect job with a first-price spray gun !

Various pneumatic guns

There are guns without cups, which do not work by gravity flow of the paint, but by "suction" : the paint inlet is located at the bottom. Variants of this gun feature pressure bowls which are very handy for applications in difficult conditions : they allow the gun to be turned in any direction without even "upside down". There are other miscellaneous pneumatic guns, such as the very special "double-nozzles" reserved for silvering or liquid products.

Chroming machines
Painting with an aerosol
Painting with an airbrush