AMF Boat Company Limited

AMF Boat Company Limited
Offshore Power - Alloy Boat Builders

Monday, April 4, 2011

Windows & Doors - Anodising V's Powder Coating

The following is an article from our window and door supplier " Seamac Aluminium" explaining the differences between Anodising and Powder Coating aluminium doors and windows in a marine environment. The difference between a quality product and an average or poor product can be all in the details. - AMF Boats

There are two forms of finishing or applying protective coatings to aluminium marine windows. There is Anodising, or Powder coating.

There is also spray painting but I do not include this as an option as I have never seen an acceptable job done this way, and many have tried!

Powder coating is a process where the mill finish alloy is etched and then covered with a fine powder of the colour required. This mix is then heated to a point where it melts and forms a hard ‘skin’ on top of whatever it is applied to. There have been many different types of powder introduced over the years, some even have a sort of Teflon in it. Powder coat it is a fairly thick film of paint and has excellent coverage characteristics. The one with Teflon is very difficult to stick or seal to, so be ware.

Anodising is a controlled acceleration of the natural oxidisation of aluminium. It is a process that involves the opening of the pores of the metal, the application of colour dyes into these pores and then the sealing and cleaning of the chemicals from the surface. This is all done in baths where electricity is applied to the metal, which causes the oxidisation to occur but in a controlled environment giving you a smooth and consistent finish. This process leaves the colour in the metal, not on it, so whatever the surface condition is before anodising, is visible afterwards. The big benefit being this finish is in the metal and will not ever flake or peel off.

As for colour fastness, powder coating is a paint and as such will fade, dry out and go powdery on the surface if left with little maintenance. Cleaning down with fresh water and waxing, as you would do with your car, will prolong this finishes ability to withstand the harsh marine environment. Anodising presently is supplied in Silver and Black. I personally have seen Silver windows that had been in the marine environment for 27 years and they showed little sign of deterioration. The Black colour, especially from the early days, does have a tendency to get a ‘blu’ish’ hint about it and can go a little flat or dry looking, but this takes many years with little or no maintenance. This is a changing of the dye colour within the pores, it is not a breaking down of the finish itself. The metal is still protected and the finish will never ‘peel or flake’.
Powder coating is a relatively heavy paint that hides many surface impurities thus less time is required for metal preparation during window production. The paint hides minor surface defects such as scratches and minor marking etc etc.
Powder coating is a bit like ‘shrink wrapping’ something. As long as the surface maintains its integrity, it is ok. But, once it cracks, or is cut, marked or stressed in anyway, moisture gets underneath and wreaks havoc on the metal. It is trapped beneath the skin and runs along underneath like an acid eating the metal away in its path. Once this begins it is all but impossible to fix. We have all seen winch handles, masts and powder coated patio furniture after a few years in the sun and rain. Yes there are good and bad powder coaters and some do a better job than others, but a film of paint applied onto the surface of most anything used in a marine environment will break down eventually, and need re-coating.
Anodising is by far the most reliable and long lasting finish for marine windows. It is hardwearing and permanent. With little maintenance, it maintains its appearance for years and will never peel or flake off. So long as the windows are glue fixed to our recommendations and totally isolated from dis-similar metals, anodising will last indefinitely.
Powder coating requires regular maintenance as does the surface of your car. If not cleaned and waxed regularly, it very quickly begins to look run down and failure is all but impossible to prevent.
SeaMac windows are all anodised unless powder coating is specifically requested or required. We supply powder coated windows at owners risk. If the finish must be white, then they must be powder coated. In NZ, there is no such thing as white anodising. Most, if not all, of our opposition powder coat their windows.
When the pro’s and con’s are spelt out to customers, almost everyone I have talked to goes with anodising. It is simply better!
I base this opinion on 42 years in the aluminium window industry, both residential/commercial, and marine. Yes we do supply powder coated windows/doors on the odd occasion, but this scenario is always pointed out.
In the case of doors on the aft wall of a vessel, this is the best case scenario as they are protected somewhat by the overhang of the roof from the sun, and, because the vessel generally swings into the wind protecting these units from the sand and saltwater blasting from mother nature. Although still not my preferred or recommended finish, in this situation there is a limited amount of ‘protection’ offered enhancing the paints ability to perform.
To summarise,
Seamac Aluminium prefers anodising as it has stood the test of time. Yes it takes us longer to prep the frames and yes we must take greater care with handling and processing, but the end product is one that will last. Does it cost more?? I suppose it must, a little bit. But the end product is something that you can rely on and trust in. Is this not worth just that little bit more???
If you are a boat builder, this is a great sales point when marketing your boats. You are not offering the cheapest option, you are offering the best available!
If you are an owner, you know you’ve gotten the best there is and your windows will look as good as they do now, for many years to come.