The previous page gave an outline of paint basics and preparing surfaces. If you are fortunate, then you might be able to strip and prepare steelwork in a quick and efficient manner, such as blast cleaning or chemical cleaning. If you are like me, then it is down to some hard work cleaning and stripping by hand.
Stripping and cleaning steelwork
Doing this by hand, comes down to scraping, wire-brushing and sanding. You might need paint-stripper too, assuming that there is any paint left! If you're lucky, paint might scrape off. Be sure to remove chunks of built up paint from rough welded surfaces, since wire brushes tend to be ineffective. I used an old half-inch wood chisel as a detail scraper. Wire brushing with an electric drill is only moderately effective, and tends to leave a glazed appearance that might still be hiding some rust. Therefore always follow up with some sanding (always wear eye protection when wire brushing). Sanding might sound like an arduous task, but it is not too bad if you buy the best sand paper available. I find that coarse aluminium-oxide cuts through most paint, and if you buy the best quality, it won't wear out and fall apart quickly. I used Oakey Liberty Green Extreme Sandpaper, coarse 60 grade.
I don't recommend power sanding, due the possible lead content in any original paint, unless you have the facilities to deal with this issue.
If there is any oil or grease present, then one should wash with a degreasing cleaner before wire-brushing, otherwise the brushing might grind the grease into the pores of the steel.
As mentioned on the previous page, AC used bitumen to coat steel parts, and this dissolves in solvent cleaners and acids.
Paint suppliers should be able to sell you suitable cleaning fluids for steel, that will de-grease and help prevent any further rust forming. This will then be rinsed off with tap water. Once dry, the steelwork should be treated with a phosphating chemical. This will treat the remaining traces of rust and will passivate the steel surface. That reduces its electrical conductivity and also creates a satin-like surface that paint will adhere to well. After it has dried out, it needs to be rinsed with de-ionised water. Then start painting as soon as possible after the surface has dried out. If you are using zinc-rich primer, then don't passivate the steel, because the zinc needs to have very good electrical contact with it.
I found that I got better paint adhesion on parts that I had crack tested (dye penetrant). This maybe because the test involved thorough cleaning with a solvent.
As mentioned on the previous page, I chose epoxy-mastic as the best primer coat for brush painting steel. It sticks well and is non-porous and also hard-wearing. I've avoided zinc-rich primer for reasons also explained on the previous page. I started out using an epoxy-mastic paint (with a 2-part polyurethane by International as a top-coat), but I got annoyed with the supplier who have their brand on that epoxy, and have since found that Jotun also do epoxy mastic, with several variations (so maybe they make the paint for that other brand?). Jotun call it "Jotamastic". International also do an epoxy primer, (plus polyurethane undercoat) but this is not compatible with single part paints, and thus can only be used on bare metal. A slight problem with the epoxy-mastic I've been trying, is how very thick it is. This is largely due to high solid content, intended to give extra protection at the expense of appearance. I ended up with a sticky mess as each thick uncured component gets all over the tins! But Jotun do a version (Jotamastic 80) which goes on a bit thinner, designed for less harsh environments. Since I don't plan to park my AC in the sea, I changed to this paint.
I'm not fussy about actual appearance of the chassis paint, except in those small areas where it will be visible. That includes the rear cross-member that is visible when you open the spare-wheel door, and also the chassis within the engine bay. One can sand this thick primer smooth, but with the risk of exposing steel on any small lumps of weld filler. Be very careful not to breath in any dust from epoxy that has not fully cured - not that you want to breath in any paint dust, but uncured epoxy carries a higher health risk.
Top coat painting
I've been painting the 2-part polyurethane top coat directly onto the epoxy-mastic, since the latter is supposed to be compatible with most other paints. Unfortunately, International Paints don't do a wide range of undercoat colours, and one is expected to mix top coat into undercoat to get the required colour. That gets complicated when you are dealing with an assortment of 2-part paints that all need mixing first!
The International "Perfection" top coat is expensive. It is easy to mix together, is quite thin without adding thinners, and brushes on beautifully. With a careful technique, you can get quite a nice finish even if you don't really need one! Since my plan is to coach-paint the AC's bodywork, I use this painting exercise to practice my laying off technique and also use top quality natural bristle brushes. Jotun also do a range of 2-part polyurethanes which are less expensive per litre, although not sold in small quantities. Unfortunately, the Jotun paint (Jotun Hardtop) is very thick out of the tin and does not spread well, going sticky in warm weather. One can thin it, although thinners come in 5 litre tins. Brush marks are very bad, although that does not matter for most areas. For those small regions that need a nice finish, I abraded the final coat with 600 grade wet an dry (used wet), and then polished it up with "T-Cut". However, if you want a gloss finish in any areas, I would recommend spending the extra money on International Perfection.
Thankfully, the AC's chassis doesn't have many hard to reach areas such as the inside of box sections. Most of the boxed chassis members have large holes on the inner plates, so that you can poke inside. I bought myself a cheap borescope that attaches to my laptop computer, enabling me to inspect the inside the chassis girders, and also check that my new coats of paints did not have any gaps. I also bought some paint brushes with a 45 degree bend, to help get into the box sections.
For cleaning and preparing these awkward areas, I used a wire-brush attachment on a flexible spindle. Sandpaper stuck to a pipe, was used to help clean any tubular sections. A few places are very inaccessible. These include the inside of the rear cross-member, despite having a hole at each end on its underside. Also, the chassis side member along a few sections with few access holes. For these, I resort to spraying in Dinitrol aerosol, having first checked with the borescope that the condition of the steel is good.
The chassis has a tubular cross-member ahead of the rear axle, but it is virtually impossible to access the inside of it while the body (or at least its wood frame) is still in place.
Brackets and fittings
The steel brackets on the chassis are mostly straight-forward to repaint. The hardest task is usually removing them. The big brackets that reinforce the door-hinge pillar, are fixed with bolts that pass through into the chassis, and coach-screws that go into the wood frame. Also screws into the pillar. It fits into a very deep slot in the pillar, which will have pinched tightly around it where the hinge bolts have clamped it. A mallet and chisel was my subtle approach to tapping it out.
If your AC has telescopic dampers at the rear, then it will have a sub-frame just behind the rear axle. The sub-frame's cross-member is a tube. To clean the inside, I stuck some abrasive paper to a smaller tube to run through the inside.
When you come to bolt the damper subframe back onto the chassis, it may be easier to do while the rear springs are off the chassis. The bolts for this (and also the axle hasps) are fitted from inside the chassis box-sections, and are tricky to insert. I fitted them after installing the springs, and my fingers would not reach far enough inside the chassis. So I wrapped the end of a length of wire to each bolt-head, so that I could poke it inside the chassis. Then I used another piece of wire to stop the first bolt from dropping back down until the frame and first nut were in place.
After repainting the fittings, the axle hasps can be given new rubber bump-stops. The originals were cut out of 3/4" sheet rubber, and I made new ones from slightly thicker 20mm sheet. They were originally held on with aluminium rivets, but I fitted small (stainles steel) countersunk machine screws, into tight fitting holes in the rubber. This will make the rubbers easier to renew in the future.
Under the rear axle, a pair of bump-plates are bolted to the chassis. The chassis underneath them is slightly concave, leaving a small gap under the plates so that they act as springs. Unfortunately, the small gap gets wedged solid with rust. So it is worth removing them to clean them up, and pack the gap with grease.
The rear bumper brackets are secured with 2 bolts (each) to the top of the square tube that forms the jacking point. One of each pair of bolts is long and passes through the tube, and acts as a stop for the jack (and tends to rust away). The other bolt is shorter, passing through the top of the tube, and its head has to clear the jack cantilever when it is inserted into the jacking point. My original bolt has its head rounded off. I found that an unmodified bolt-head will clear the jack if its flats are parallel to the tube. I couldn't fit a spanner inside the tube to hold the bolt, so I inserted the jack and tilted it to hold the bolt firmly.
My rear chassis had escaped any structural damage. But there was some pitting on the sides of the main side rails at the rear end. This was where the plywood boot side panels were bolted on, acting as a water trap. The pitting increases the water trap, creating a vicious circle. Therefore, I filled it smooth with a suitable epoxy filler.
I believe a thin layer of clean grease is the best protection to add to the finished paint. Grease must not be used where it might come into contact with wood. For these areas, use Waxoyl. In fact, I prefer to use Waxoyl for all the external steel, rather than alternating between substances. Mineral oil and grease must also be avoided where it might get onto any rubber parts. Online discussions I've read, suggest that clear Waxoyl won't damage rubber parts. For the inside of box sections (and tubes), I sprayed Dinitrol ML using their extension tube. Dinitrol ML is the thinner version of their rust prevention products, ideal for cavities. The extension tube nozzle sprays outwards in a 360 degree pattern.