November 22, 2008 at 5:08 pm #1198Ed StoneForum Participant
During the restoration of my EC10 (see article in the ‘Show and Tell’ section), I stripped and restored the aluminum casting font panel. Many radios include aluminum or alloy castings that have paint flaking off due to age and poor storage conditions, so here is a little post covering how to re-finish these parts.
The first thing to appreciate is that aluminum is a highly reactive metal – it oxidises very quickly. This is counter-intuitive to the layman as aluminum stays bright and shiny for extended periods, unlike steel, which is much less reactive. Why? – its because the layer of aluminum oxide that forms is very thin and virtually invisible. This layer, only a few molecules thick, protects the surface from further reaction. Under adverse conditions however, eg. very humid, warm or changing temperatures etc, this coating does not afford adequate protection and the surface starts to become dull and white powdery oxide deposits can be seen over time. If the surface is painted, minor imperfections in the paint (eg. pinholes, shrinkage cracks, chips etc) allow moisture to penetrate and react with the underlying aluminum surface, weakening the alumium/paint bond. This is particularly a problem when the original paint was not applied correctly.
To re-finish an aluminum panel/part, first strip off the old paint (scraping, stripper etc) and clean the aluminum surface with steel wool. Wipe off any aluminum dust with alcohol or other solvent, ensuring that your fingers do not then re-contact the part. Apply two coats of a suitable primer (check out your local car spares store and read the back of the primer cans – several types are made specifically for aluminum). These types of primer bond to the freshly-formed aluminum oxide surface and reduce the risk of the overlying paint detaching over time. The primed part can then be sprayed with the desired final finish.
I have used this technique on several aluminum front panels and parts with complete success. The EC10 front panel is shown being re-finished below. In this case, the panel was not completely stripped – only the flaking paint was removed prior to re-finishing as described above. Paint having a good bond was left in palce and the edges ‘feathered’ as you would when touching-up paint on a car – use 600, 1200 then 1500 grade ‘wet and dry’ emery paper for good results.
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