This article follows the completed journey of the gate that we were riveting up in the last but one blog ‘Making gates’.
After that video clip was taken, the gate was completely hot riveted up. The locks and fittings were checked for correct alignment and operation and all the ground markers and set up indicators chiselled in.
During the time between that and this article, the gates had been delivered to specialist finishers. The finishers shot basted the metal to clean and create a ‘key’ for molten zinc to be sprayed manually on to the surface to create a cathodic protective layer (Hot zinc spraying). This layer provides electro/chemical protection of the mild steel gate frame….. I’m conscious not to be too technical here.… meaning most of the zinc has to be corroded away before the mild steel gets attacked by rust.
The gate is then primed, undercoated and top coated in the conventional way, we use synthetic based vinyl paints, but with the cathodic protection in place, you could specify any suitable coloured exterior finish. Whatever the finish, as long as the zinc coating is not exposed too much to the elements by way of a sensible maintenance schedule the Ironwork should unlimited service and exceptionally longer than a painted finish alone.
Time to install the Ironwork, with the paint finish cured and safe to handle, we fitted the gate into its final position as seen it the photo above, in this case we dug holes and concreted the hanging panel and closing post in to the ground. We use a product known as PostCrete, to which we add large aggregate and water, having already spaced and levelled the ironwork ‘tails’ in the holes we hard pack the dryish mix in; within 30 minutes the ironwork structures are ready to accept light/controlled loads. We always ask the client to limit use during the first 48 hours, so the foundations have a chance to cure properly.
So, why hot zinc spray? We want our work to last as long as economically possible (as do our customers), Hot Zinc Spraying offers delicate or detailed mild steel structures the best balance between protection against rusting and retention of hot forged detail. The last thing we want is our beautiful work covered in a thick coating of ‘whatever’; this may be ‘very’ desirable for lesser craftsmen, but not us! So in short, painted, quality exterior Ironwork where detail and textures are important, always specify Hot Zinc Spraying prior to a paint system being used.
An Important note to Professionals and Specifiers! Hot dipped Galvanising or Electroplating should not be specified as an acceptable alternative to Hot Zinc Spraying. It should be specified for the reasons in ‘Why hot zinc spray?’ (previous paragraph). Hot zinc spraying is sometimes referred to as Metalizing and is related to a thermal process known as Sherardizing. Electroplating is a cold process and uses a surface application of zinc to inhibit corrosion on iron and mild steel, but due to the very thin coating of zinc applied it is not suitable for long term exterior applications. There is a limit to the size and shape that can be treated in Plating and Sherardizing processes and to a greater degree the Hot dipped Galvanizing process,; there is no size limit to Hot zinc spraying, as the treatment (and its prep-process, shot blasting) is brought to the metalwork opposed to the metalwork being presented to the treatment.