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Old 31st July 2002, 01:24 AM   #1
jteef is offline jteef  United States
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Default Painting tips

the next few pieces of electronics(pre, speakers, aleph) that i build are probably going to be painted. Not that I don't like the look of a nice finished metal, but a couple large hunks of aluminum in my living room isn't very pleasing to me. (no, I do not intend to paint the heatsinks)

so to practice, i thought i would try first on my computer case(who likes that beige color anyways?) results have not been very promising so far. I am using a krylon high gloss blue spray and krylon high gloss clear coat spray. I sanded the metal with 320 grit wet sandpaper until it was reasonably smooth. Then put on the first coat of blue, it looked alright at that point but there were some areas you could tell did not have the same coverage as elsewhere. after drying for 12 hours i wetsanded that again with the 320 grit and applied a second coat of blue. This is where things turned bad. after drying the finish looked really patchy. some places had a glossy look, while others were almost satin. the "brush" strokes, if you will, were very apparent. I sanded that and applied a 3rd coat of blue really aiming for even coverage, but with the same poor results. so i moved on to the clear and matters got worse. so I've got a few questions i hope somebody can answer.

would i benefit at all by using a different paint maybe? like a testors spray enamel? or any other suggestions? what is the vishay of spray paints?

i was holding the can about 6-8 inches away and using long sweeps across the surface(~24"x24") The directions on the can said to keep it 10-12" away but when i tried that it seemed like it would take 3 or 4 cans of paint to complete the exercise. (there was a gentle breeze outside maybe 1-2mph but it was clear this distance was very inefficient at getting paint on the surface. I've been painting on my driveway and then moving to my temp controlled garage(~80F in the summer)

I only have the one coat of clear on now and plan to use 600 grit wet paper between coats. Is this OK?

should i sand the last coat at all? or just use some kind of a car polish/wax?

last, a friend suggested i buy an old oven/range from a swapmeet or flea market and get some DIY powder coating material. Any experience with this stuff?

thanks

jt
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Old 31st July 2002, 04:48 AM   #2
Duo is offline Duo  Canada
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From what i've learned, don't sand the paint between sprayings, this is what causes brushstroking effects. I'm not completely sure of this, but I have painted things like that and I don't sand between coats and it seems to work fine.
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Old 31st July 2002, 10:50 AM   #3
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if you really want to wet sand betwen coats you need to be using a 1000+ grit wet or dry paper. i wouldnt do it with spray enamal. i might do it before the clear coat but not between coats. preperation is everything when your painting as the final coat will only look as good as what it was sprayed over. you can fill minor imperfections with a good sandable primer and/or glazing putty. the final sanding before paint should be done with like an 800 grit paper and after that the surface needs to be really really clean. when you spray try to put on enough paint to keep the surface wet all over so that the paint will flow out evenly. and if your not sure what kind of paint that you are painting over use a primer sealer before the paint, use it after the all your prep is done and do not sand it, just wipe it down with a surface prep solvent and a tack rag. hope this helps.....................mike
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Old 31st July 2002, 01:54 PM   #4
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Well, I have some experience with paint on cars. Single layer coats are much, much easier to work with than those two layer coats of a metal effect something and a clear coat.

Heating the can to 50C will help because the paint escapes with more pressure, resulting in finer drops and more paint really deposited on the surface even if the can is not too close.

When applying another layer on top (no matter whether color or clear paint), make sure the old paint has had 24 h to dry. Some, not all paints may start to crinkle if another layer is applied in the first 0.5-24 h.

If you apply another layer of the same paint, sanding usually helps. Start with 320 or 400 paper to remove drops and striae. Finish with 600 or 1000. My impression is that the new paint distributes itself better on a sanded surface and has less of a tendency to form droplets compared to an unsanded surface.

Once the final layer has been applied, you can sand it with 1000 paper to remove all dust particles, striae and haze. Finally, you have to polish it with car polishing paste (the stuff for paintwork, not the wax polish that is meant for freshening old cars). A bad toothpaste, i.e. one that is not meant for sensitive teeth, should also work fine.
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Old 31st July 2002, 02:45 PM   #5
dc is offline dc
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Does the advice above also apply to clear-coating aluminum cases?

I've tried to finish a couple of anodized cases with polyurethane (one with spray and one with a brush) and both of them came out looking like sh!t. I sprayed them with Fantastik, first, then used some paint thinner to clean them before applying the first coat. One has brush strokes and the other has uneven, gobby/dry spots all over.

Are multiple coats a good idea? Can I sand with 600 grit or higher wet/dry sandpaper or a 3M pad between coats to take down high spots? Should I be using something other than polyurethane? Does anyone have a favorite brand?

I guess I'm going for a smooth, semi-gloss finish.

Thanks.

Brad
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Old 31st July 2002, 04:09 PM   #6
tiroth is offline tiroth  United States
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This may not be helpful, but I used FinalKote UR (urethane) to coat some copper to prevent oxidation. It came out looking great.

This is the stuff intended for use on circuit boards.
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Old 31st July 2002, 09:17 PM   #7
jteef is offline jteef  United States
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thanks for the tips. I will try to post some pictures of what i am talking about. digicam isn't doing a very good job at picking up the errors though. i am just gonna try to make my finish mirror-like right now since i ran out of clear and practice again on something else before i start on the important stuff.

The finest sandpaper i've got is labeled 13 micron. I dont know how this translates into grit. I used it for the last sanding step before the polish/wax when i had my truck painted so it should be alright.

I think my problem with the finish is just getting a good even coverage, but i haven't figured out how to get good coverage yet...
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Old 31st July 2002, 10:19 PM   #8
jteef is offline jteef  United States
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so while the last piece was drying i tried to get a good finish out of one of the remaining and things started looking up. I think now that using the 320 grit between coats was the definite problem. the 13 micron paper i used cleaned up the mess quite a bit. and was just enough to get rid of the orange peel texturing. After a good cleaning, I put on 2 coats of zymol car cleaner wax and the finish turned out presentable at least. not quite mirror, but i attribute that to previous use of the 320 grit (you can still see the marks it made if you look close) and only having one coat of clear on that piece.

jt
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