Filling and painting anodised aluminium

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Earlier this summer, whilst rafted in the Medina River, some "kind" person decided to nurf my boat with his anchor. Unfortunately our boat was left unattended at the time and he (or she) didn't have the decency to own up or pay up. Fortunately, the damage was fairly minimal and certainly could have been a lot worse but it has sratched and chipped the anodised aluminium tow rail. Luckily I have located some special paint which is almost an exact match but to make a perfect repair I will first need to fill the small indentations in the aluminium. Has anyone got any advice as to the best filler and primer to use and whether it is best to fill and then primer or vice versa?
 
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Any repair to anodised aluminium will be a compromise between convenience and longeivity.

However if the component doesn't work or flex significantly you could get reasonable results.


The primer you want is zinc chromate two pack. Cut back the aluminium to bright metal, any white corrosion left will cause the repair to fail. Straight away after cutting back apply a thin layer of the primer. Thick coats have no advantage as you are just etching the surface to give a good key to the filler. In fact too thick a coat will introduce a stratum of non durable material which itself will fail, so just one thin coat. Then use an epoxy filler in the normal way.

Now here's the problem:- anodising behaves like a Teflon pan, nothing (including paint) sticks to it so unless you can very carefully just coat the filler any paint that gets applied to the surrounding anodising will soon flake off. You might ask " how about using the primer on the anodising?" Well it won't work since the anodising will do it's work in preventing the chemical etching taking place. It is a problem. Anodising will, like galvanising, "self heal" to a limited extent but this applies only to minor scratches and your damage sounds more major.

Steve cronin
 
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Many thanks for the excellent reply Steve. The info you have given will be extremely useful.

John Copson
 
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