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Although this step is not absolutely necessary, it is certainly a good idea if you want to achieve a really good result. Also I wouldn’t recommend doing this with ordinary primer/surfacer as it is usually not thick enough to rub back.
The first step is to grab yourself a pressure-pack can or tin of black acrylic if you don’t mind using the spray gun again. Usually a decent sized pressure pack can will be sufficient for most cars, just be sure it is acrylic not enamel as enamel will react with the top coat acrylic if there is even the smallest trace of it on the panel.
The next step is to spray a light coat across your panels. Read the instructions and allow enough drying time before sanding.
For the next step I use 800-1000 grit wet and dry paper used wet and with a sanding block. Once again you want to follow the lines of the panel and keep plenty of water on the surface. As you can see (hopefully!) from the pictures some of the repairs that we did are far from perfect and although the door looked good these imperfections would have showed up after the top coat was on. Hence the reason to use a guide coat!
The beauty of high-fill primer is that 99 percent of the time you can sand out these imperfections without the need for more filler or reaching the bare surface below. Be extra careful at the edges of the panels as it is easy to sand through the primer there and as with the speed file, don’t be tempted just to sand one little area to get rid of all the guidecoat, keep the sanding block moving across a large area until all the guide coat is gone. If you do happen to sand through the primer it is simple a matter of applying some more primer and a guidecoat to the area and sanding again.
Once you think you have sanded the entire panel wash it down with clean water and check for any remaining guide coat, re-do any problem areas and finally either dry the panel with compressed air or leave it out in the sun for an hour or two.
An important note regarding primer - 99 percent of primer/surfacers, spray putties etc are porous meaning that they will absorb moisture. The amount of time between applying the primer and the top coat should be as little as possible and once the wet sanding is finished be sure to dry the panel down as much as possible. Any moisture trapped in the primer has the ability to ruin our nice new paint job. Not good!
Part Five, in what is steadily becoming the longest diy tutorial in history is all about applying the primer to the repaired panels.
A quick note before we begin. Always check the local rules and regulations regarding the use of automotive paints. Often times it will be illegal to spray these paints at your home and you may need to look for an alternative location. In a lot of cities you can actually hire out spray booths by the hour or day/half day and this would be better than upsetting everyone and maybe even facing a fine.
And remember always use a respirator or at the very least some sort of mask. Automotive paints are not kind to the body, plus if you’re off with the fairies the job will probably end up looking pretty ordinary! As you can see my choice of mask does great things for my looks but doesn’t offer much in the way of protection and it scares the hell out of the kids! Seriously though it is very important to always protect yourself.
Always wear a mask while spray painting!
Some Important Basics
Now that we have that out of the way I guess the first step is to go through a few basics before we start the painting.
There is going to be a fair bit of bog (filler) dust around if you have done a repair or two and all of this needs to be removed before painting begins, both from the panels and the surrounding area. Compressed air is good for this however you need to either blow it all out in an area away from where you are going to paint or allow enough time for the dust to settle and then hose the floor down. Be as thorough as you can when cleaning down the panel as any muck that is remaining might just find it’s way onto your lovely new paint surface.
Obviously anywhere that we don’t want the paint to go has to be masked up. A newspaper and medium thickness masking tape will do the job. Be sure to mask every little nook and cranny that you don’t want to paint as over-spray finds it way into everywhere and there is nothing worse than spending a day or two removing it when you could be polishing your new paint job instead. Things like door handles and lights are best removed in my opinion but if that is not possible try your best to take the masking tape right to the edge so you have a nice clean finish.
Final Preparation.
Before we move on it is very important to wipe the panel/panels down with wax and grease remover. The idea is to use two clean rags, one to apply the wax and grease remover and one to dry it off. Once this is done ensure that nothing comes in contact with the surface as even the grease in your skin can affect the adhesion of the paint. A ‘tac cloth’ can be used after this to remove any remaining muck however I don’t find this absolutely necessary.
More Reading!
.Next item - the spray gun. There is two types that are suitable for automotive paints, the suction feed and the gravity feed gun. For applying primer both types are suitable but I have found that for the best top coat results a gravity feed gun is the way to go. Once again I stress that I am not a qualified spray painter or panel beater, this is just what I have found works for me over the last ten or so years of spraying cars. I picked this gun up from ebay for about 80 bucks and for what I do at least it has done very well. The suction feed gun was retired a while ago and from memory it was a Super Cheap job for around the 40 dollar mark. Certainly not high quality but they are good enough for an amateur like myself.
The next thing is the primer itself. If you are keen to get a really good finish on your car I suggest you use high-fill primer or spray putty and spend the time wet sanding it once applied. If you just want to get the colour on and are not too concerned about minor imperfections a primer/surfacer will do. We are focusing on using acrylic paint with this article as two-pack, in my opinion, is best left to the professionals with the right equipment such as a booth, respirator etc.
The first step is to work out our thinning ratio. Generally speaking acrylic top coat and primers are thinned at a ratio of 1 part paint to 1½ parts thinners. Use only thinners suitable for acrylic paints, enamel thinners won’t do anything! This ratio is only a rough guide and it should be clearly stated on the tin what ratio is needed for that particular product. We are using an acrylic high fill primer and general purpose thinners and our ratio is 1 to 1½.
I have an old paint gun pot that I use for mixing the paint and have found the best way to measure the amounts is with a metal ruler. It is important that you give your primer a thorough stir before use, it could have been sitting around for quite a while and the heavier parts may have sunk to the bottom. Once again the old metal ruler is good for this. I also suggest wiping the top of the primer tin and thinners container before pouring. As a rough guide you will need about half a litre of thinned primer per panel for a medium to large size car. Before starting it is a good idea to mix up some paint and test your skills on something other than the car.
Which brings me to another point. The spray gun will more that likely have at least two adjustable controls. Your best bet here is to try each one and get a feel for what is best for you. Just a couple of pointers - you want the paint ‘fan’ to be reasonably wide but with enough paint material coming through to maintain a nice ‘wet’ edge. See the video below for an idea of what I consider a good paint flow and pattern.
Air pressure - most acrylic products that I have used recommend a spraying pressure of around 30 psi. I however find that I can get far better results using anywhere from 40 to 50 psi. Now I am not saying that use should ignore what is written on the label but I think the more time you spend practicing and changing around the settings the better result you will get simply because you can get a feel for what works best for you.
Finally, applying the primer.
Ok, on with it already! I will explain as best I can the actual painting procedure and suggest that after reading this you take a look at the video below which should make things clearer? Hopefully.
To start with, what we want is a nice even flow of paint onto the surface. Too little and we will have dry areas that are rough and the paint will be thin, too heavy and we will get the runs ( figuratively speaking). It all comes down to how fast we move the gun and how much paint is being sprayed.
Something that I found took a bit of practice is keeping the gun parallel to the panel. Particularly at the edges it is easy to lift the gun away from the panel. Try to be almost robotic in your movements and keep the gun at the same distance from the panel across the whole stroke. As you do each stroke you want to overlap the previous one by half. This ensures that there is no ‘dry’ areas towards the outside of the paint ‘fan’.
The best method I have found in maintaining a nice even coat is to position yourself and/or the lighting around you so that you can see the ‘wet’ paint edge at all times. We tried to capture this in the video although it may be a bit hard to see. If you can follow this wet edge across each stroke you will get a feel for how fast you need to go and whether or not there is adequate paint coming from the gun.
Well that is probably enough from me, take a look at the video and if you have any issues or questions I will be making a new topic on the Advice Forum so feel free to post them there. It’s late and I’m buggered but I think I’ve covered everything regarding applying the primer but if you feel I’ve left something out please let me know!
Next we will cover using a ‘guide coat’ to achieve a better finish and then get on to applying the top coats.
Our VN’s panels are in pretty good condition however they have not been immune to the usual shopping trolley dents and with the passengers rear door being the worst we thought we would start there.
I find it easier to remove the panel from the vehicle if possible, having a damaged spine makes it almost impossible for me to work on vertical panels but you may find it easier with the panels left on the car.
Ok, so our door is all over the shop and would look pretty ordinary once the top coat went on but instead of trying to repair every dent individually we are going to use the speed file to identify each dodgy area and then put a thin layer of filler over the area. Once sanded down with the speed file we should, in theory, have a nice straight panel. Once the primer/filler has been applied we will be doing a light guide coat and sanding the primer to ensure we have all problem areas covered. More on that a little later.
The first thing to do is to strip the door handles, trim pieces etc so we have a nice flat surface to work with. Then we take out the speed file and start the hard work. After about twenty minutes of sanding this what we end up with, a true indication of where the high and low areas of the panel are. The pictures aren’t the best I know and silver is not a good colour to illustrate this but on this panel there are many areas where the sandpaper has not touched (low areas that need to be filled) and areas where all the paint has been removed (high areas that need to be tapped down).
After a little bit of hammer and dolly work on the high spots we then start to apply the filler to the low areas.
And after an hour or so with the speed file this is the result. All things being equal we should now have a nice straight door ready to undercoat. I used 80 grit paper on the speed file and 120 grit with a sanding block to finish it off. We are using a high-fill primer/spray putty as our undercoat but if you plan on using just primer/surfacer I suggest going to a finer grade paper to finish the panel. Primer/surfacer is not very good at covering sanding marks so they all need to be removed before applying it. High-fill primer is a little more forgiving.
A quick note when using a speed file - when sanding down the filler you might be tempted to sand across the panel to flatten out any ‘ridges’. Usually if there are areas of filler that are not sanding down flat while sanding with the lines of the panel (see directional arrows on pic) those areas will need more filler. A thin coat over these areas will smooth things out and keep the lines of the panel straight.
In Part Five we will cover apply the primer - finally!
