If you live near the coast where salt laden air is all around, or want a long lasting, easy to maintain coating for your trailer, galvanising is the way to go.
A bit of extra money and some extra preparation will give your new trailer the best start to its new life.
Galvanising is the application of 99.5% pure zinc which through preparation and correct dipping methods effectively bonds the galvanising to the steel almost permanently.
The zinc coating will dull with age and does require cleaning now and then and any damage to the trailer can be touched up with zinc enriched paint if required.
Just beware if you leave your grass clippings on the trailer for too long as the acids in the rotting grass will drip through and effectively strip any galvanising it touches. As well, if you live near the sea, wash the salt off the trailer on a regular basis.
You can paint a galvanised trailer once the shiny zinc coating has oxidized and dulled. Don’t waste your time painting a newly galvanised trailer, the paint will just flake off.
If your trailer is to be galvanised, it is imperative that a couple of easy to follow rules are applied before purchasing or welding any steel work. Firstly make sure that any steel is unprimed and without any varnish or coating. For a start it is very uncomfortable welding steel with a coating fuming and smoking (and potentially damaging to your health), secondly it will need to be removed before galvanising and this can be a pricey and time consuming job.
Zinc needs a nice clean steel surface to adhere to so if the box section steel you are building your trailer with has an internal coating you are only getting half the corrosion protection you could be getting with clean steel.
It is mandatory that tubular fabrications and hollow/box sections are properly vented with either open ends or drain holes where sections are butted together. Any pickling acid or rinse water that may get trapped in a blind or closed joint connection will be converted to super-heated steam and can develop a pressure of up to 3800 psi when immersed in molten zinc at 450°c. Apart from making your chassis look like a bloated and distorted fish, there is the potential for an explosion within the galvanising bath and is a serious potential hazard to galvanising equipment and people.
Simply stated, the chassis must be lowered into the acid/rinse/galvanising baths without trapping any air. It must also be raised from the baths without trapping any solution. Trailer chassis’ are normally dipped side down on an angle to allow the fluids to flow over and through the trailer. Consequently, ample passageways which allow flow in and out must be designed into the chassis. Since items to be galvanised are immersed and withdrawn at an angle, the vent holes should be located at the highest point and drainage holes at the lowest point in each hollow member.
To comply with the rules of galvanising, notches or holes need to be made in some parts of the chassis. The minimum size of the holes need to be at least 7mm in diameter (it pays to check with your galvaniser on what they require) – Check this page to see where the drainage holes need to be - Pre-Finishing.
Lastly, anything oil based like cutting fluid (water based cutting fluid is OK) for drilling or cutting and also things like crayon or sharpies for marking and writing on the steel work can prevent good adhesion of the zinc to the steelwork.
Sharpies are particularly bad especially if you are in the habit of doodling your artwork on the bare steel prior to galvanizing. Your artwork will show through the galvanizing so be warned.