SPRAY GUNS

You will also need a spray gun, of course. There are three main types of gun (conventional, HVLP and LVLP), and two styles for DIY use (suction and gravity-fed) to choose from. Conventional guns are those that were standard through the 1980s. You can still buy them and, with the right size tip, they will spray any type of paint. They are the cheapest to buy and still give excellent results, making them ideal for low-volume users. The only real weakness of a conventional gun is that it only has a transfer efficiency of around 35%, which means that only an average of 35% of the paint leaving the gun actually ends up on the panel.

High Volume Low Pressure (HVLP) guns were developed to achieve a much higher percentage of paint on the panel, but require a larger compressor, and also larger bore hoses to take out restrictions in the airflow. The relatively coarse atomisation they achieve made them best suited to waterborne base coats, but newer designs reduce the amount of air that is needed for the same performance, and these are usually referred to as Low Volume Low Pressure (or LVLP) guns.

A suction-fed gun is the classic style, with a metal paint cup hanging underneath. Having all the weight under the hand generally gives them good balance, even with a generous 1-litre paint capacity that helps stretch the area you can paint before having to stop for a refill and so risk getting a dry edge. They can be more difficult to keep clear of wet roofs than the gravity-fed alternative though, and the cup can leak paint through its vent hole if tilted too far.

Gravity-fed guns are generally much smaller, with an inverted plastic paint cup sitting above the gun. They

can work off a very small amount of paint for minor touch-ups, whereas the pick- up pipe in a suction gun never quite empties its pot of paint. There is no difference in terms of coverage or spray pattern compared to suctionfed guns, but the gravity-fed tool's ½ -litre pot does limit how much you can cover before having to stop and re-fill. Having that weight above the hand can also make them tiring to use for long periods, although good tools can still achieve excellent balance.

Air is pushed out the narrow ring around the needle in the centre to pull the paint out. The other holes in the cap atomise the paint and control the spray pattern. HVLP guns have a much wider gap around the needle in the centre than either conventional or LVLP guns, but they can all get blocked, especially if the spray pressure has been set too high causing paint to bounce back off the panel and hit the gun.

A traditional suction-fed gun like this is generally robust, well-balanced and has a generous paint capacity.

Small gravity-fed guns can get a very fine and narrow pattern which makes them ideal for smart repairs and minor touch-ups, but they will only be worthwhile if you continually deal in such work as you can achieve similar effects by turning down the pressure on a standard tool. The fluid tip on a suction or gravity-fed gun must be 1/32in proud of the air cap to create the necessary vortex for correct spraying. (It sits flush on the more expensive pressure-fed gun used in some professional environments.) Suction guns have filters over the pick-up pipe. There are different grades for different paints, and too fine a filter will soon clog up when used with metallics, for example. Filters are even more important in gravity-fed guns because any specks of contamination in the paint will sink to the bottom of the cup and get sprayed first. You can get different fluid tips for different paints, and the picture shows (from left to right) 1.2, 1.8 and 2mm tips. If you can only afford one, then the best general-purpose options are a 1.6 for a conventional gun or a 1.4 for the latest LVLP tools and gravity fed guns. Air caps also come in a number of sizes, with a 110 cap being favourite for solvent-based paints.     