ProXL
ProXL
Let’s look at five problems often encountered with clear spray lacquers and how these can quickly be resolved so you can create a professional spray lacquer finish.
Bear in mind that this article is aimed at those using a spray gun system, although there are things to learn for those using our handy 1k aerosol spray clear lacquers and 2k aerosol clear coats.
A spray pattern can sometimes be uneven, with the spray heavier on the top or bottom, left or right. This can be caused by a blockage at the horn holes, the fluid tip, the cap or the tip seat.
Start by making a test spray pattern, then after rotating the cap by one half-turn make another test spray. If the heavy patch rotates with the cap, the cap needs to be cleaned. If it doesn’t rotate, look for a fine burr on the edge of the fluid tip. This can be removed with 600-grit wet and dry sandpaper.
If this doesn’t resolve the problem, look for dried lacquer just inside the opening. Washing the components thoroughly in solvent should remove this.
If you are using a pressure feed system and the spray pattern is significantly heavier in the centre, this could be caused by the fluid pressure being too high in relation to the air pressure: the lacquer flow will be too high for the air cap to cope. Adjust the air and fluid pressures until you achieve the right balance.
If this doesn’t correct the problem, or if you’re not using a pressure feed system, the spreader adjustment valve setting may be too low. Try adjusting this to widen the spray pattern, as this will distribute the lacquer more evenly.
Another cause of this problem is when the lacquer isn’t atomising properly. This can be due to the lacquer being too thick or the lacquer flow setting being too high. If the lacquer is thinned to the correct consistency, reduce the fluid flow setting.
If you’re using a pressure feed system and the spray pattern is shaped like a figure of eight or even split entirely, this may be caused by the fluid feed pressure being too low in proportion to the air feed. Increase it slightly, taking care to not unbalance the two pressures as this can cause excessive spray in the centre of the pattern (see the previous section in this article).
If that doesn’t resolve it or if you’re not using a pressure feed system, try reducing the air pressure. Another cause can be when the spreader adjustment valve is set too high, so check that too.
This problem can be caused by a badly seated spreader adjustment screw or a loose air cap. Check the position of the adjustment screw and if it won’t sit properly, replace it. Tighten them both and see if this resolves the problem.
The first detail to check if this is happening is the level of lacquer in the reservoir, particularly if you’re using a siphon or pressure feed system. Refilling the reservoir should resolve this easily. Also, make sure you are holding the spray gun upright so that the lacquer can feed consistently.
If this doesn’t fix the problem check the fluid needle packing nut, making sure it is lubricated and tight.
Obstructions in the lacquer flow will also cause sporadic spraying, particularly if you’re using 2k lacquer that has been mixed for a while and might be starting to solidify. Back-flush the system with solvent to remove any obstruction and if you suspect your 2k lacquer, clean the system out thoroughly and mix a fresh batch.
Finally, check the fluid tip, seat, tube and inlet nipple to see whether any of them are loose or damaged. Replace any damaged parts and make sure everything is properly tightened.
Increasing the length of the air hose from your compressor to the spray gun can also improve the evenness. This is down to something called laminar flow. When the air first leaves the compressor there will be a lot of internal turbulence, but as it progresses along the hose this settles down into a smoother flow.
If you’re getting just air and no lacquer coming out of the gun, increase the material flow by opening the fluid adjusting screw or if you’re using a pressure feed system, increase the fluid pressure at the tank.
Even though you are only getting air feeding through the gun, this problem can also be caused by there being insufficient air pressure to atomise the lacquer. If increasing the fluid flow/pressure doesn’t work, try increasing the air pressure. If this works, you may then need to rebalance the air/fluid mix.
No spray at all, not even air? First, check the air supply and airlines. If you’re using an intermittently running compressor and air tank, has the compressor switched off due to an overload or blown a fuse? Is there a kink in the air hose?
Next, take a look at the fluid needle adjusting screw. Is it open enough?
If you’re using a suction feed system, check that the lacquer isn’t too thick as this can prevent the suction action. Also check that the gun has been fitted with a proper air cap and tip for suction feed, as an internal mix or pressure feed air cap and tip won’t work on a suction feed system.
If you’re using an internal mix cap and pressure tank, try increasing the fluid pressure at the tank.
One factor that can cause excessive overspray and fog is having the atomisation pressure set too high, so if you’re getting both problems, try reducing the pressure.
Overspray can also be caused by working too far away from the surface (you should be spraying from about 8 inches or 20 centimetres) or from using an incorrect spray technique. Stay parallel to the work surface and work at an even pace.
Excessive or fast-drying thinners can also increase fogging. If you’re using the correct thinners and the lacquer is too thin, you can add some unthinned lacquer, but if the thinners are too fast you may need to mix a fresh batch.
All types of spray systems can leak from the packing nut if it is loose, or if the packing is worn or dry. Check the packing and lubricate or replace it then tighten the packing nut, taking care to not cause the needle to bind.
If you’re using a pressure feed system, you may also get leaks or drips from the front of the gun and this can have several causes:
Many factors can affect the quality of clear lacquers for metal including technique, spray settings and compatibility between the lacquer and its underlying substrates, but here are three commonly-encountered problems and their likely causes.
Most likely to occur when spraying a vertical surface, running and sagging can be caused by the lacquer being thinned or applied excessively. If the lacquer is too thin you can try adjusting the gun (or if you’re using a pressure feed system, reducing the fluid pressure) and applying it in several light coats, but you may need to mix it again with additional unthinned lacquer.
Running and sagging can also happen if you are holding the gun at an angle rather than perpendicular to the surface, or if you are advancing the gun too slowly. Adapt your technique until you resolve this.
If the lacquer dries before it has had time to flow it will develop a coarse, sandy finish. To prevent premature drying, start by studying your settings and technique.
Try a test spray pattern and reduce the air pressure until it looks right.
Don’t spray too far from the surface: aim for a distance of about 8 inches (20 centimetres).
If neither of these suggestions fixes the problem, check the manufacturer’s mixing instructions as using incorrect thinners can also be a cause.
This thick, dimpled finish can be caused by surface contamination, incorrect mixing, settings and technique.
To prevent orange peel, start by thoroughly preparing the surface. Use fine grit paper to remove any paint nibs or sanding marks and thoroughly clean it to remove all traces of dust, dirt and oils.
Follow the manufacturer’s instructions when mixing your lacquer with thinners, making sure you use the correct thinners for the lacquer and that they are thoroughly mixed together.
Dimpling may occur if the air pressure is too low, so you may need to increase the air pressure or decrease the fluid pressure. Spray a test pattern and adjust the settings accordingly.
Don’t spray too close to the surface: again, you need to aim for a distance of about 8 inches (20 centimetres).
