The spray gun is superior to paint brushes and rollers in both performance and quality of painting. However, using it is a little more difficult than using a brush: so that the result of painting does not disappoint, you must follow some rules.
The spray gun is more demanding on the condition of the painted surface. With a brush in several strokes, you can at the very least paint over dusty, non-sanded and poorly wetted surfaces. With a spray gun, this will not work – the paint will not penetrate into the roughness, and it will simply roll off the stained surfaces, no matter how many layers of luggage. Therefore, the surface must be cleaned, dried and degreased before painting. Rough and damaged areas should be putty and sanded. It is advisable to clean smooth (glossy) surfaces with fine (P240-P600) sandpaper until matt, then remove dust and degrease.
All unpainted areas should be covered with polyethylene and masking tape.
Many paints can only be used within a certain temperature range, which is usually listed on the paint can. Make sure that the air temperature at the place of painting is within acceptable limits.Provide good ventilation in the area of painting – when using a spray gun, harmful substances are emitted much more than when working with a brush or roller.
Make sure there are no open flames, hot objects or surfaces in the work area – sprayed flammable paints are highly flammable.Paint preparation
The viscosity of the paint must be within a certain range. If the viscosity is too low, the paint will run off and form drips.
The compressor power of electric spray guns is limited, it may simply not be enough to push paint that is too viscous through the nozzle. You will have to urgently clean the tool, moreover, it may fail altogether. Therefore, electric spray guns are especially demanding on the viscosity of the paint.
But pneumatic spray guns are not “omnivorous” either. If the viscosity of the paint is higher than the permissible value, it will lay down unevenly, creating “shagreen” on the surface.
For electric spray guns, the permissible range and method of measuring viscosity are usually given in the gun manual. If the spray gun is equipped with a viscometer (a device for determining the viscosity), it is better to use it before pouring paint into the spray gun tank. A simple viscometer is a container with a calibrated hole. The dishes are filled with paint, then the time until the paint flows out through the hole is timed.
If the viscosity of the paint is higher than the recommended one, it is thinned in the amount of 5% of the paint volume. Thereafter, the viscosity is checked again and the dilution is repeated if necessary.
The type of thinner depends on the composition of the paint:
Oil-alkyd and acrylic paints – white spirit.
Glyphthal and bituminous varnishes – solvent.
Nitrocellulose enamels and primers – Thinner # 646 (although any 645 to 650 can be used except 648).
Acrylic, water-based and other water-dispersion paints – pure water. Keep in mind that water-based paints can be thinned with water no more than 10% by volume.
If there is no viscometer in the kit, the viscosity of the paint is selected during test staining.
Preparation of the spray gun
The spray gun can be equipped with nozzles with a hole of different diameters. The nozzle is selected based on the type and viscosity of the paint.
Solvent-based base enamels and water-based paints are the most liquid, for them nozzles with a hole of 1.3-1.4 mm are used.
Acrylic, alkyd enamels and primers are sprayed through a nozzle with a hole of 1.4-1.5 mm.
For the application of leveling fillers, a nozzle with a 1.6-1.8 mm orifice is required.
Liquid putties are applied through a nozzle with a 2-3 mm hole.
Before installing a nozzle with an orifice larger than 1.5 mm, make sure that your compressor is powerful enough to handle such viscous paints – the gun manual should indicate the minimum compressor capacity and operating pressure for using certain nozzles.
After installing the nozzle, check the print:
Fill the container with the prepared paint. Adjust the paint supply to maximum and, if possible, air supply using the appropriate regulators. Electric spray guns usually only have paint flow control.
Set the nozzle guide horizontally to form a vertical plume.
Bring spray gun to test surface at working distance. It is indicated in the instruction manual and is usually from 10 to 30 cm. As a test surface, you can use any smooth material – paper, cardboard, wall section – on which the paint will be clearly visible.
Hold the gun perpendicular to the test surface and pull the trigger fully for one second. An oval print should form on the surface.
A correctly adjusted spray gun will give an evenly colored oval of the correct shape with blurred edges.
If the stain looks different, adjust the spray gun:
Keeping the instrument at a working distance from the test surface, carry out a test painting by slowly moving the gun horizontally along the surface. The tool should not be guided along an arc, but parallel to the surface, keeping the distance to it and keeping it perpendicular.
Without releasing the trigger, paint the second strip of paint down, overlapping 50% of the first strip. Make sure the paint is of the right quality. It may be necessary to change the viscosity of the paint or the distance to the painted surface if pebbles or smudges appear. Do not move to the work surface until a satisfactory test result is obtained.
If necessary, dilute all the prepared paint to the desired consistency.
If necessary, reshape the torch by rotating the nozzle. Vertical surfaces are painted with horizontal passages, while the torch must be vertical. When painting horizontal surfaces, it can be painted with vertical passes, with a horizontal torch orientation. This may be required for wood surfaces – it is better to paint them in the direction of the wood grain.
Start painting at one of the top corners of the surface, and guide the tool in a straight line at a working distance, keeping it strictly perpendicular to the surface. The next strip is applied below the previous one and overlaps it by about 50%. Change the grip of the gun depending on the height of the strip to spray at right angles.
If the surface is too long to paint over its entire length in one pass, divide it into 0.6-1.5 m sections and paint them one by one. When moving to the next section, grab 10-15 cm of the previous one when painting.
Allow the paint to dry before applying the second coat – drying times between coats are usually given on the paint can.
After finishing painting
The spray gun must be cleaned immediately after finishing work. If paint residues thicken inside the gun, it may break.
The remaining paint from the tank should be drained into a paint can, rinsed with a solvent and cleaned. Then you should pour a small amount of solvent into the tank, fix it on the spray gun and spray for a few seconds – this will clear the tract of paint residues. But paint may still remain under the seals, so you should disassemble the spray gun, thoroughly clean all parts and gaskets with a brush soaked in solvent, rags or rinse them with solvent.
The nozzle holes are cleaned with a special brush or toothpick. Never use metal objects to clean the nozzle – even slight damage to the nozzle can lead to uneven spray of paint and, as a result, deterioration of the quality of painting.
Then the parts should be dried, the instrument should be assembled. The spray gun is ready for new use.