As with most things, preparation is the key to painting your new trailer. Hopefully the trailer has not been exposed to the elements and started to show signs of rust, as this will just make the job harder. If you have been using un-primed steel, there a couple of options for preparing the steel surface prior to priming and painting.
Sandblasting, shotbasting or soda blasting is the best way to remove any surface contaminants, rust, paint and mill scale. It gives the best surface finish for primer and paint to key into and will give the paint its best chance for a long life. It will also help tidy up any sharp edges and clean up any left over bits of slag on your welds. Unless you do it yourself, this option can be reasonably expensive, especially when you factor in the transporting the trailer to and from the sandblasters.
Once the trailer is blasted, it needs to be primed as soon as practically possible to prevent any moisture or contaminates affecting the bare surface.
Check with your paint supplier for a good chemical cleaner that is compatible with the paint you want to use. You will need to invest in some rubber gloves and protective body covering, safety glasses and possibly a respirator and use them when applying the cleaner. Chemical cleaners can be applied with a squeegy bottle or paint brush and cleaning can be enhanced with stainless or brass wool. Scotchbrite pads may work, but may also dissolve or breakdown with the chemicals. Follow the directions for application and clean up and wear your protective equipment. This is a reasonably priced option although outfitting yourself and the potential mess you produce and have to clean up can make this a bit inconvenient.
This is the quickest method of cleaning up the tailer prior to painting, but does require a bit of effort. Either a wire wheel or scotchbrite disc used on a hand grinder or hand drill will remove the majority of the mill scale, rust and contaminates. Flapper wheels used on a hand grinder will get into the most difficult places and give a very good finish to the steelwork and are great for tidying up messy welding and sharp edges. Again, make sure your are using a dust mask, ear protection, glasses and gloves before getting stuck in. It pays to give the trailer a good dust down after cleaning up.
Using a good etch primer, spray or brush the steel as soon as practically possible after cleaning, as this will seal the steelwork and prevent any airborne moisture from causing any surface corrosion. Be sure to lift the trailer on each side to get paint under the chassis, mudguards, spring hangers and drawbar and try to get as much paint into the drawbar and any open cavities as possible without making a mess. Etch primer tends to have a lot of VOC’s (Volatile Organic Compounds) which help the paint to bond with the steel and to assist in drying and hardening. The VOC’s also play havoc with most peoples health and while you may not feel any effect from them while painting, you will notice it the next day or two as your body tries to get the toxins out of your system. Use a good respirator with cartridges designed for the primers and paints you are using to minimise any effects of the paint.
Ideally a 2 pot paint system will give you the best long lasting, hard wearing finish and needs to be applied with a spray gun to give the best finish. You need to accurately mix only the amount of paint you need to fill your sprayer each time and accuracy in measuring everything to the nearest gram is essential to make sure that the colour and drying is consistent.
There are plenty of one pot metal protective paints on the market and if sprayed onto the trailer will give you a reasonably good wearing finish. If you don’t have access to a good spray gun, aerosol cans are a last resort, convenient although expensive. As with the primer, VOC’s will give you more than a headache, so wear a good respirator and have plenty of ventilation in your painting area. One thing also to remember when spraying paint around, any paint that comes out of the sprayer that doesn’t go on your trailer will go somewhere and will normally coat everything in the surrounding area. Cover everything up that you do not want painted, including the floor.
If you decide to galvanise your trailer with the view to painting it, you have a couple of options. Paint will not adhere to newly galvanised steel. It may look nice for a day or two and then start flaking off and looking worse than a dogs breakfast. The zinc coating on your trailer needs to oxidise either naturally by waiting 6 months or so until the surface shine dulls off, or by using an acid wash to etch into the galvanised surface. If you decide to wait until the surface oxidises naturally, give the trailer a good degrease with a proprietary cleaner or solvent and then apply an etch primer and paint as if it were bare steel. If you can’t wait and want your newly galvanised trailer painted, talk to your paint supplier and apply the product they recommend prior to the trailer being etch primed and painted or better still get your local car painter to acid etch it and etch prime the trailer for you. This will ensure you get some sort of warranty on the job if the paint starts falling off from an improper job.