Never painted ali before and I will have some cast ali guttering to repaint.
The plan is to pressure wash the guttering sections on the ground (they will be off anyway) to remove crud and loose paint. Sound paint stays on.
The finish is to be black.
I'm not sure of what brand of etch primer and top coat to go for.
Also - does it matter if you etch-prime over exisitng paint, or do you just avoid those parts?
Cheers!
Tim
I don't suppose it matters much. If the surface is well weathered it helps. Hammerite used to make one I have used in the past, seems to be OK.
The purpose of etch primer is to form a bond to metal, usually zinc, so putting it over existing paint is of no benefit. Some etch primer is clear stuff, some just looks like normal paint.
I used a zinc chromate primer bought from a marine chandler and intended for boat use. That was on new aluminium guttering in the 1980s. It is still sound, but I don't recall the make this far down the line, even if it is still made.
Colin Bignell
Probably International if it was for a boat.
Tim Watts wrote: [snip]
You can't etch prime over existing. Ideally you should take the paint back to bare alloy. When sanding it is best to use aluminium oxide paper and avoid the use of wire brushes. The brushes leave short bits of steel embedded in the alloy and this will cause corrosion.
Thanks Steve - that is something I would not have figured out - and I would have tried a wire brush at somepoint.
I will see how far I get with a pressure washer to take off the grot and flaky paint - I guess if there's a lot of paint left I will just have to prime upto sound stuff - I don't have the spirit to be sanding everything - there's 30m of the stuff.
Finish is not vastly important - just want it "generally black" and "mostly not falling off" - which is why I'm reusing the ali :)
Unless of course I could get a wet sandblasting attachment for the pressure washer.....
Cheers!
Tim
It is possible to apply acid etch over original paintwork but it may also react with existing paint (and has no effect) particularly if it is a synthetic base. Acid etch primer in many instances can be applied over recent paint finishes if it is very lightly sprayed over the top but not brushed on, areosol and brushing etch primers are available on the market, the spray type will dry very quickly which should help avoid solvent penetration or reaction which is the main cause of paint reactions.
Acid etch primer should also be applied very sparingly (one coat only) and the overlapping edges can simply be scuffed off with a piece of 600 paper, acid etch only needs to be inked over the surface to provide a suitable key, it does NOT need a heavy coating to obliterate the surface.
Any modern alkyd type synthetic gloss paint will suffice for guttering, but you should still use a synthetic primer before the gloss.
Stephen.
You can (at least for some brands of pressure washer) e.g.
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