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I have a set of folding doors (interior <-> exterior) that have been badly scraped and scratched during a renovation project. I have purchased the correct colour touch up paint from the manufacturer, but there are no instructions on how to apply.

My initial thoughts are that I should sand down the area with 60 then 120 grade paper. Clear the area with white spirit and then apply the touch up paint. Does this sound about right? Is there a better way?

The finish of the frame is very smooth. Im worried that if I use a paint brush it will be streaky. What applicator should I use?

Note: the white area is what's left of the protective plastic, my concern is the abrasion below it.

scratches

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    Don't go anywhere near it with 60. If the sand is brown it's still too coarse, use the black stuff. – Mazura May 22 '16 at 21:13
  • why not use 60? – Gaz_Edge May 22 '16 at 21:15
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    60-grit is coarse even for woodwork. On metal it'll result in scratches so deep that you'd spend a great deal of time working them out with 120, and again with 240. Simply put, with metal the working depth is much shallower than with wood, and the grit gradations are finer. – isherwood May 22 '16 at 21:23
  • @isherwood thanks - didn't know that - what would you're recommendation be for moving up the grades? – Gaz_Edge May 22 '16 at 21:24
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    @isherwood thanks - the other 'blemishes' are just dust that will wipe off, plaster splashes, and a few paint flecks that will wipe off. The big bit of white you can see is protective backing. – Gaz_Edge May 22 '16 at 21:38
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do exactly what you described just as you described. put four or five coats on. then:

1) sand the new paint very carefully with 800 gr sandpaper. use wet/dry paper and use water to lubricate. use a block of wood as a backer to make sure you dont get too much pressure in one area or another and sand through the paint. sand down until smooth and flush with adjacent paint. dont worry if it looks flat and dull now.

2) repeat with 1200 and then 1500.

3) buff the repaired area and the adjacent area with a smooth cotton cloth (t shirt will do fine) with some brasso, toothpaste, or some other polishing agent. polish with hand pressure and the polishing agent on the cloth until you get the same overall gloss to match. more rubbing, more shine.

4) if a smooth finish is desired, you are done. if you want a brushed finish (like many aluminum panels) rub very lightly with a scotchbrite pad in the same direction as the grain you are trying to match.

done!

  • I don't know about 4~5 coats, but all in all, yes. – Mazura May 22 '16 at 21:16
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    @mazura - all depends on whether you want a professional touchup or just a diy butcher job. most commercial aluminum is powdercoated with polyester. its typically 3-5 mil thick (.003" to .005"). however, the touchup paint is inevitably lacquer based enamel. with even a coarse brush, you will only be putting on 2-3 mil per coat, but it will dry down to half that. ergo, you need 4-5 coats to build up 8-10 mil coating depth. then you will be sanding half of it down to get rid of the brush strokes - leaving you with a final depth of 3-5 mil – personal privacy advocate May 23 '16 at 13:47
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It depends if the doors are wood or metal and if the paint is latex or oil based.

You must get the doors very smooth, and steel wool might work best. The best way to apply the paint would be a sponge applicator, or use a brush then a sponge applicator to get the brush strokes out.

What's critical is to use the same based touch up paint as what is already on the door. You can use oil based on oil based or latex, but not latex on oil base without using a bonding agent/primer first.

  • the doors are aluminium as stated in the title. The paint was supplied my manufacture and can be applied direct – Gaz_Edge May 22 '16 at 20:01
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A better easier way would be to buff out those scuffs with a buffing wheel.

If you want it optically flat, you'll need multiple coats of paint and sanding in between them.

Aluminum does not like to sand, it likes to gall, and it readily sullies sandpaper. You would need an "abrasive cleaning stick" for a larger project, but it looks like you'd only go through a few pieces of paper for that job (if any).

That being said, all you're going to do with sandpaper, is make smaller and smaller gouges: you can either buff it out, or put on so many coats of sanded paint that it just 'disappears'.

  • I hesitated to post an answer, because I'm talking about how to work with aluminum, this is not just simple surface prepping for paint. – Mazura May 22 '16 at 22:24

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