Priming Aluminum

[Quetzalsailor]

I have spot primed my aluminum mast using Primocon, an Interlux product sold for underwater use on freshly-sanded aluminum outdrives and similar, as well as a barrier coat between bottom paints. Instructions say, in plain English, that this stuff cannot be used above the true waterline. Given that even outdrives are taken out of water and left in boatyards over winter, and noting that the solvents and thinners used in applying Primocon are the same as for their Brightside Polyurethane, I decided to use it anyway.

I emailed Interlux's technical staff and they said to get the Primocon off and do the job over with proper primers. What do you suppose is going on here? (I mean, other than my testa dura working overtime?)

--screaming at self-inflicted pain in Maryland--

[Hirilondë]

Do a search in the forum using the key words "zinc and chromate"(include the and). You will find tons on the subject.

[Quetzalsailor]

Yes, the zinc chromate (it's the yellow, thin coating) is the usual primer for aluminum, applied after the correct etch (Alodine), within the requisite time. Interlux sells their answer which is Epoxy Primecoat, also used after their etch (Vinyllux Primewash).

Being a lazy so-n-so, and because I've used both of these, and they're a pain, and expensive in small doses, and I wanted the job done now, I talked myself into the Primocon.

I had a nice, helpful, long interchange with one of Interlux's technical folk. He did not say why the Primocon had to be used solely below the true waterline. He did say that the Brightside Polyurethane is not compatible with the Primocon and that it probably would not cure, that it would remain gummy. I think that it did appear to cure, but I'll see what it looks like tomorrow, after nearly a week. He said that there may be long term durability issues as well.