C[omp]ute

From: andrew cooke <andrew@...>

Date: Sun, 4 Oct 2015 17:14:40 -0300

I just painted an aluminium bike frame.  Here's what I did - hopefully I'll
remember to follow-up in a year or so with some details on how well it has
lasted.

After asking on Reddit, I found that the big problem with painting an
aluminium bike frame is that paint that "sticks" to aluminium long-term is
very hard to find.  So instead of stripping the paint, I simply sanded it
smooth and painted on top of that.

The frame (Marin Iron Springs) had quite a lot of detail, which I assumed was
transfers.  But when I started sanding it turned out (as far as I could tell)
to be quite a complex multi-layered, apparenetly stenciled, paint job.

I used 100 grade wet and dry (dry) paper to sand things down, focussing
particularly on raised edges.  With care, nowhere did I do through to the
metal.

I then placed vaseline on the headtube caps, used masking tape to seal off the
bottom bracket and headtube, and blu-tak to block screw holes, before
suspending the frame from the headtube on a ceiling hook on the balcony (which
was lined in sheets and newspaper).

Before painting I used alcohol wipes (I have a pile because of MS injections)
to give the (now washed and sanded) frame a final clean.

A single can of RustOleum grey primer was sufficient for two initial coats
(the second after some sanding to remove a run, mainly because I found I had
missed behind the seat post!).  The primer was good for learning how to spray
without runs (not hard really - just take your time and use "mini layers",
letting things dry for a minute or so between passes).

After that, I used two cans of pale blue (some cheap make sold locally), for
two top coats.  The first didn't cover well, but after the second things
looked pretty solid.

Each coat (of 4) was done a day apart.  I wet-sanded (320 grade, gently) and
cleaned with alcohol wipes between the two top coats.

The final finish was what I would call "satin".  For gloss, I think you'd need
to wet-sand and then add a clear top coat.  But I like how this looks so am
stopping here.

Unfortunately I am working next week, so assembling the bike will probably
take some time.  On the other hand, it's probably better to give the paint
more time to dry.

Andrew