Applying coatings to wood
In principle, the elements should be coated before their assembly. A good surface finish requires certain rules to be followed. One of them is painting elements lying down, which has the following advantages:
- enables precise control of the uniformity of the coating application by reflection of light from the plane,
- allows you to apply a fairly thick layer, which does not drain off the element,
- allows a more comfortable position during work.
The disadvantages of this method of coating include the amount of room for drying elements and the possibility of damage to the coatings during assembly.
The thickness of the applied coating should be as large as possible. However, it is limited by the following factors:
- some varnishes tend to fold,
- some of the varnishes easily flow down oblique and vertical planes,
- other varnishes break easily and lose their shine.
Only certain types of varnish, e.g.. polyurethane and epoxy can be applied in a thick layer (consumption until 0,25 kg/m²).
The most frequently used methods of surface finishing include applying varnish with a brush. This is admittedly inefficient, but very simple. Flat brushes 4-10 cm wide are used for larger surfaces. Observe the following rules for brush coating: unidirectional brush strokes do not guarantee even application. The direction of the brush movement should be changed three times (drawing).
Drawing. Brush varnishing method: I - the first coarse spreading of the varnish along the fibers, II - spreading the varnish across the fibers, III - the direction of the final brush strokes.
Only narrow paneling strips can be varnished with a one-way brush movement. If we are forced to varnish paneling while standing, we first lead the brush vertically, then horizontally and finally vertically again (drawing).
Drawing. A method of varnishing a vertical wall with a brush: And - the first, vertical brush strokes, II - horizontal varnish distribution, III - final spreading of the varnish with vertical brush movements.
This way, we will prevent the varnish from flowing down the vertical plane. With such cross-spreading of the varnish, you should not paint too large an area, a square with a side is enough 60 cm. The method of painting the vertical wall is shown in the drawing.
Drawing. Sequence of varnishing a vertical wall with a brush (the lacquered field has an area of about 0.4-0.5 m²). Sequence of painting the fields from top to bottom and from right to left (or vice versa)
After painting, just like after each painting, brushes should be thoroughly washed. Solvent cleaning is so tedious, that even after washing several times, we will not achieve satisfactory results. The brush will always partially harden because some dirt residues will remain in it, and these, the next time they are painted, they create a rough surface. We will get rid of troublesome and prolonged washing, using a special brush cleaner with the symbol - P 8203. Washing the brush in this preparation causes the varnish or paint to become water-soluble. Then rinsing under running water gives the brush perfectly clean. The preparation is suitable for cleaning brushes from most varnishes and paints. The preparation used should be poured into the original packaging, because it can be used many times, until it is too thickened. Therefore, it is recommended to remove excess paint from the brush before each wash. In the preparation of P. 8203 you can wash brushes with hardened, old paint, even two-component. The brushes, however, should be left immersed in the preparation for several days.
It is not recommended to apply the varnish with a roller on wall and ceiling coverings. Painting external wall coverings with a roller is particularly not recommended, because the varnish will not get into the gaps, easily penetrated by water. However, a roller for varnishing floors is very useful.
Applying the varnish with a spray gun is the best way to apply a coating. In industry, even more perfect ones are used, mainly more efficient coating methods, e.g.. electrostatic method. However, it requires relatively complex apparatuses, equipped with pressure equipment, pressure tank, reduction valve, air filter and pressure gauge. Connecting the high pressure spray gun directly to the compressor, e.g.. for pumping car wheels, is unsuitable due to the pulsation of the air and the possibility of water and oil from the compressor getting into the gun.
The low pressure spray gun can be connected to a powerful vacuum cleaner. However, the vacuum cleaner must be perfectly clean, prevent dust particles from entering the gun and paintwork.
The Mistral or Ever-spray spray gun is a high-pressure device with its own suction and pressure pump driven by an electromagnet powered from the mains voltage 220 V. The surface is covered relatively quickly and evenly. Cleaning the gun is easy, but with short-term work (small surface to be painted), often much longer than the varnishing itself. Therefore, it is better to paint small surfaces with a brush. Thoroughly cleaning the gun is very important, because paint residues are left in it, especially with two-component varnishes, will cause the spray nozzle to stick. The gun should be cleaned according to the manufacturer's instructions. After cleaning, the camera can be smeared with sewing machine oil, which, however, should not be poured into the tank. Pour a few drops into the throat of the gun, turned upside down. Even with careful cleaning of the gun, sometimes the nozzle clogs up. You can tell it by the soft sound made by the pump. In this case, do not disassemble the entire gun. Also a repair of such a tool, it is redundant in most cases. We propose the following procedure: unscrew the nozzle and take out the spring, i.e.. parts, which are disassembled each time the gun is cleaned. Into the hole, in which the piston works, insert gently a punch with a flat end, diameter approx 2 mm. Tapping carefully with a hammer. This way we should release the stuck plunger. Then we turn on the gun to the network. If it does not work properly, we repeat the steps. Be very gentle with the device during the operation, in order not to damage the plunger.
When spraying the outer surfaces with a gun, it is formed, especially with some varnishes, fog, which can even travel several meters. Even at this distance, the paint particles adhere perfectly to any surface (windows, door, car, fruit trees etc.). Therefore, such places should be selected for spray painting with a gun, in which there is no risk of accidentally "targeting" other objects.
The spray gun moves in a straight line. The width of the paint mist cone is adjusted depending on the size of the painted surface.
When spray painting, varnishes and paints should be thinned, adding 5-15% thinner to them. A much larger amount of thinner evaporates during spraying than when painting with a brush. Therefore, it is essential to ensure intensive ventilation in closed rooms. So it is better to varnish the wooden parts outside, and then moving them to closed rooms. Leaving freshly painted items outside, especially in the summer, causes insects to stick to the varnish layer. You should also not spray paint anything in the wind.
Spray varnish during spraying, which will not settle on the painted surface, behaves differently, depending on the type. For example. cold-curing synthetic matt varnish, at a distance of approx 2 m from the atomizer turns into a fine white powder, which can be easily swept up. All nitrocellulose varnishes and pore fillers behave in a similar way. Epoxy and polyurethane varnishes settle on the floor in sticky form, microscopic drops. It is then recommended to cover the floor in the immediate vicinity of the workplace. When spraying slow-drying varnishes, their micro-droplets are in the air. A longer stay in such an atmosphere causes the deposition of the varnish in the breathing system of the painter. In such cases, it is recommended to use a gauze filter band over the nose and mouth.