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There have been many developments the area of primers in the last several years. Laquer primers were the standard for many years and was/is used under laquer and enamel paints. Laquer primers have fallen victim to the EPA because the VOC content and the thinner used with them. Enamel primers can into being and had a very short (thankfuly) life. Multi-stage Primers (multi part) are now in use because of the problems with laquer primers and the newer paints. The paints in use now do not work well with laquer primers. In fact DuPonts' Chroma Base paints will actually lift laquer primers and products. The newer primers are basicaly imprevious to the common solivents and thinners (reducers). The multi-stage primers come in various price ranges and designed for various applications. Duponts' URO Prime costs about $177 per gallon. Their second line, called Nason, is almost as good but only costs about $80 per gallon. Others have prices about the same range. Some primers require a certain amount of reducer (converter) other have a range of amounts you could use to cover various applications. All will require a certain amount of activator in order to start the chemical curing process. Too little and the primer will take hours or days to dry. Too much and the primer will set up in the cup before it is all used. All will require a mixing stick to get the proportions correct. Epoxy primers dry very fast. Laquer had to be sprayed on "dry" in order for it to dry resonably quickly and to prevent shinkage. Multi stage primers dry in a matter of minutes and do not shrink (much) as they dry. They do have one draw back but after some experience you will learn how to overcome this. The problem is that they have a very short pot life. Left to set in a cup at shop temperatures, they will harden up and then set in a matter of an hour or so. Placing the gun in the fridge will extend the pot life to 2-3 hours. Do not take the gun out of the fridge and open it however, as this will let warm air into the cup and cause condensation in the cup. Not good. Just spray what you need and return the gun to the fridge. If you do not need very much primer at the time then by all means do not mix more than you need.
DO NOT LET THE PRIMER SET UP IN THE GUN. Should that happen you might just as well throw the gun away. I have tried to clean guns after this has happened but it never sprayed right after that.
In days gone by, metal had to be etched with a seperate solution in order to give a surface that primer could stick to. Now we use a "self etching primer" to give a metal the necasary surface with which to work. Bare metal is spray with these self etching primers first, allowed to dry the required time, then sprayed with the primer-fillers. By the way..... .. A gravity fed gun is the best way to go with these high dollar primers. Less waste, lower air pressures mean less over-spray and you can mix the primer thicker for faster coverage. Doesn't have to be a high dollar gun. My primer gun came from Harbour Freight and only cost about $40. Works well and should something happen I haven't lost $300 for a professional grade gun. Save the bucks to buy the top coat gun(s).
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