Prepping & painting metal garage door?

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Hi all. After some pro advice here please.

Standard metal up & over garage door. In white and several areas have delaminated back to clean metal. Don't think it was prepped correctly in the first place and then was painted with hammerite.

I need to repaint it but could do with tips about how much to strip... Don't want to end up fighting the bonded areas but also not sure about the peeled areas having different finish levels to the final coat(s).
Want to avoid visible blemishes. Have read about using white spirit to wet rub and achieve graduation, but info was a bit thin on the process/techniques.

I haven't got a month of Sunday's to do this, so really after the trade approach to balance time and effort with results that would satisfy most.

Many thanks. D
 
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I am assuming that the doors are galvanised metal. If so you will need an appropriate primer.

Calcium Plumbate is often used but it is lead based. You can purchase spray cans of self-etching paints if you are only covering small areas of bare metal.

Personally I would feather out the edges of the sound paint. Start with 80 or 100 grade paper and finish off with 180 silicone carbide paper (before priming). Use the 180 grit over the hole door to provide a "key". Then apply a coat of oil based undercoat to the primed areas and follow up by undercoating the whole door. Then lightly sand the feathered areas if need be.

Then apply one or two coats of oil based gloss.

If applying two coats of gloss rather than one, ensure that the second coat is applied within 2 weeks (it will negate the need to lightly resand the first gloss).

Alternatively use a waterbased paint if you don't care about longevity, or use a cellulose paint such as Hammerite if you aren't worried about the quality of finish.
 
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Thanks very much for that @opps
Good instructive info.
I'll spend an hour at it with a scraper and see what comes off easy and then reasses the plan of attack (y)
 
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Don't be too aggressive though.

If you scrape (or sand) through the galvanised finish you risk compromising the weatherproofing protection. A fairly blunt scraper would be preferable to a sharp chisel.

Best of luck.
 
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Oh, BTW, other tips that might be useful.

If you are going down the oil based path, add some terebene to the paints to help them harden/cure faster.

Do not apply the gloss late in the day. At this time of the year, if you wait until 5 pm to apply the gloss, the evening dew may well start coming down about 7pm or 8pm and is likely to cause the gloss to blush, that is to say, the gloss may end up with semi-matt finish.

If you try to apply the gloss on a cold day, you will find that it seems thicker and drags a lot. Add some Owatrol oil, it isn't cheap though. If you were painting timber, simply keeping the paint warm might suffice but you are applying paint to a cold surface.
 
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I did mine earlier this year, white to black with flaking paint the same as you describe.

I scraped all the loose stuff off and sanded the edges then used car body filler to fill the slight imperfections.

Once sanded, primed and painted it looks great.
 
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