Another dose of technical stuff for those of you who have been complaining
about not getting enough meat with the fat...

I'm working on a department store erected in 1938.

The shopfront display windows are aluminium (aluminum for those on the other
side of the Pacific), and originally had a golden orange coloured finish
which the press of the time referred to as anodising.  This makes sense from
our understanding of the history of anodised aluminium.

The original finish is very soft, and has clearly worn away in places.  It
was overpainted at some time in the past, probably in the 1960s or 1970s.

We are planning to overpaint again, as it is not feasible or appropriate to
dismantle the windows and return the aluminium sections to the factory to be
reanodised.  Besides which, that would destroy the evidence of the original
anodising.

However, we are debating whether the existing paint coating should be
removed.  I don't believe it has a very good bond to the anodising, and am
concerned about the quality of adhesion of a new coating.  The heritage
architect is concerned about damage to the original anodising during
stripping.  Any takers on this one?  Anybody with experience?

Elsewhere on the building are aluminium windows and awning soffit cladding
which appears not to have been anodised, and which has also been painted in
the past.  The press of the time referred to a satin-finish, which to me
suggests that it was buffed in the factory but nothing else.

Naturally, there is some pitting corrosion of these elements, but it is not
extensive.

We are planning to strip the paint, buff or grind back the aluminium to
eliminate most of the pitting corrosion, and then ... I would prefer to
leave au naturel, but again, the heritage architect would like to overpaint
in order to prevent further corrosion.  I believe that regular (once/year)
cleaning of the aluminium should minimise the development of pitting
corrosion, and therefore we are likely to get better service from the
material without it being coated than if we coat it with a clear sealer and
need to replace the sealer on a 10-15 year (maximum) cycle.

Any thoughts or comments???

Cheers

david