Primer
Primers have come a long way in the past decade or so. It is refreshing to see “lacquer type” primers are rarely used today by body shops. While easy to use, they offer little rust protection or holdout, especially under today’s catalyzed finishes. You can build your house on mud or build it on concrete – a solid foundation is the beginning of a long lasting, quality finish. The current crop of primers include epoxy, etch, 2 part urethane primer fillers, 2 part polyester primer fillers and primer sealer value coats.

When dealing with bare substrates such as aluminum or steel you need to start with an etch primer or an epoxy primer (one or the other) to promote adhesion of subsequent fill primers and in the case of steel, to protect it from rusting. Due to agreements between major auto paint manufacturers over environmental concerns, most products are chromate free (or in the process) which is good and bad, as zinc chromate would actually galvanize metal giving extra rust protection so it is very important that the metal is really clean. On stripped parts look for signs of black dots in pitting (the visual sign of rust starting) and try to wire wheel, fiber wheel or grind it out as best you can. There are now available small right angle die grinders (air) that take roll-loc type spin on fiber discs (in 2 and 3” diameters) that are great for getting into the nooks and crannies and cleaning with out grinding. Metal conditioners are a mild acid you use to wipe off light surface rust prior to priming. When dealing with new fiberglass or plastic pieces it is important you clean in a variety of steps to get rid off the mold release waxes. Start with soapy water and rinse and dry, then wax and grease remover – wipe and dry, and finish with Isopropyl Alcohol. Remember to change your wipers often, as you don’t want to recontaminate your cleaned surface.

Most quality primers today are two part, they are mixed with a second component (an activator or hardener) when they are to be used and have a limited pot life so follow the manufacturers recommendations. The urethane and polyester primers use an isocyanate type of catalyst so you need good ventilation and a proper respirator when you use them. The mixed left over will have to be disposed of and you will need to clean your spray gun thoroughly with lacquer thinner after use. The catalyst in epoxy primer is isocyanate free but you still need to wear a charcoal mask and have ventilation.

On a serious restoration, we generally recommend epoxy primer as opposed to an etch primer. The epoxies can take polyester (plastic) fillers over them and are closest chemically to the e-coats the factories now use to keep vehicles from rusting, they are also superior for fiberglass and will work on most plastics (including flexible ones). Some epoxies are non-sanding and require a fill primer applied after (follow the manufacturers recommendations). When two part fill primer started appearing a lot of people in the trade thought they would fill anything (such as 24 grinder marks), not the case, you should still finish your bodywork with a minimum of 120 grit (I prefer 240) to be sure you do not get some shrinking down the road. Many of the two part primers are tint-able with paint so you can use less colour for coverage and have less obvious chips. There are also several coloured primer sealers, which are used as a final prime before painting, usually wet on wet (applied and left un-sanded just before painting). Like tint-able primer they afford quicker coverage of colour and less noticeable chips and add some extra adhesion and sealing of bodywork and any broken edges. New plastic parts sometimes require special plastic primer and cleaning as per fiberglass (above) prior to painting.

If you are painting over an existing finish, you should prime all feather edged areas and bodywork with a two-part fill primer. When applying, extend each coat past the previous coat so you don’t get a high build on just the repair area. This will prevent cutting into the surrounding paint when sanding the primer, which can cause swelling around the repair area when you paint. Final sanding of primers should end with a minimum grit of P800 (European grading) or 400A (American grading) prior to painting, any finer than P1200 or 600A can result in poor paint adhesion. It is often necessary to prime and block then re-prime several times to get panels straight. On the first blocking, you will probably need to use 80 or 120 and finishing with 180-220 before priming again.

It is vitally important you “guide coat” your primer so you can see if you have sanded enough. This can be done by simply applying a light spray bomb coat over the primer in a contrasting colour, I prefer to add a bit of black base coat to my primer gun and some urethane reducer and give the primed areas a quick coat right after priming (as this helps clean the gun and melts any dry areas). When you begin sanding, you sand off the paint dots so you know it has been thoroughly sanded and not too much. In all cases it is important to follow the manufacturers recommendations for mixing, dry times etcetera. While it is not necessary to use the same brand of primer as the paint brand it is not a bad idea in case you run into problems – paint manufacturers will only stand behind there products if they are used right through. In restorations, you often run into areas that require very high filling. While technically not a primer, polyester spray fillers can fill far beyond even the highest build primers. They are really a liquid form of two-part polyester putty, except sprayed on, allowing a more even application and are easier to sand than putty. The best ones come from Europe where they have used these for years in restoration. They usually require to priming before painting.

When applying primer, you should do a pre wipe of wax and grease remover, then apply the first coat light (partial trigger) and apply subsequent coats like paint – smooth and wet. Primer guns generally have a bigger fluid tip than topcoat guns as the solids are higher in primer and you are trying to fill. Most primers are applied at around 35-40 psi (conventional gun), it is important to let the primer flash off between coats (go dull) to not trap the solvents so it will cure properly. Make sure your air source is clean and free from water and oil – any contamination in the primer can resurface as a disaster when painting. If you get any fisheyes during priming – it is imperitive to sand them out (after curing) and re-prime these areas - to seal them off or they will appear when painting.

The products used today are far superior to what was available in the past and when used correctly will last the life of the vehicle. We hope this de-mystifies the current products and you can start your project like a pro.

John