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Old 10-23-2011, 09:22 PM   #1
Gruesome OP
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spray painting BMW system case lids

I have decided that my bike needs to be a bit more conspicuous for commuting duty. The black system cases blend into the background a little too well.

Experience so far:
The color match from automotivetouchup/microfinish for BMW Mandarin 414 seems to be quite good. Initially I thought the base coat was too orange, but on the bike it looks about right, at least before the clearcoat.

The cans, nominally 12 oz, hold a bit less than that: 11.2/11.4 oz is the difference between full and empty for the two cans I've used so far. The spray tips make a very fine mist, lighter than on other brands I've used. Very even spray, just a little bit of occasional sputtering towards the end of the can.

A can of base coat goes less far than I thought. I ordered prep solvent, adhesion promoter, base coat and gloss clearcoat from them; unfortunately the adhesion promoter does NOT double as a plastic primer; it is clear. The yellow base coat without primer does not go very far on the black system case lids: one can does not cover both lids without black showing through. Two cans seem to do the job.

I did not completely sand/smooth out the dimpled surface structure of the case lids. It still shows after the base coat (and my plan was to keep it that way), but the clearcoat might fill it in.

The base coat went on beautifully, but the clearcoat seems to attract flies like crazy, and picking them out of the wet paint is not a good idea :-(

Anyways, that's my experience so far.
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Old 10-24-2011, 06:52 AM   #2
henrymartin
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Did you go with catalyzed clear?

As for the dimples/texture. If you want to remove it on any future projects, SEM high build primer seems to be the ticket. Spray and wetsand to a smooth finish.
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Old 10-24-2011, 08:19 AM   #3
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Nope, all single (component) spray cans; base coat says 'acrylic urethane', clearcoat 'acrylic lacquer'. Do they make two component paints in cans? I've read that two component stuff is better, but so would be baking it on or having a proper spray booth...

Regarding the dimples: My intent was to keep the structure, hoping that would show small imperfections less. But now it looks like the clearcoat will fill the dimples in, whether I like it or not.
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Old 10-24-2011, 09:27 AM   #4
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SprayMax and a couple of others make a clear 2k urethane in a can. It has some pin to pull, which will mix the the parts and then you have a certain amount of time to spray. I'm currently investigating the option myself as i have two tanks to do this winter.
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Old 10-24-2011, 02:49 PM   #5
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Pics

Thanks, just saw your other thread. I don't think it's an option for me anymore, mixing coats from different suppliers seems a big no-no. I already got the first heel scuff on the right lid - probably a good thing to get that out of the way....

pics:


added reflective striping:



Gruesome screwed with this post 03-02-2014 at 08:07 AM Reason: fix picture links
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Old 11-27-2011, 02:51 PM   #6
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That looks excellent! I've had bad results painting (or attempting to paint) plastics. How happy are you with yours right now? Any secrets to share?

I'm considering this for a pair of lids on a r1100s system case, they were originally smooth finished but previous owners have scratched and dinged them up extensively.
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Old 11-29-2011, 10:59 PM   #7
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even more info...

I'm still very happy with the paint job on the case lids. Even though not using primer was a bone headed move. I think the paint brand was a good choice; initially I thought the cans were pricey, but after comparing quart prices I think automotivetouchup is actually one of the cheaper brands, and, as I said, in my case (Mandarin 414) the color match is excellent.

Masking using 13 gal garbage bags pulled tight over the case bodies worked great. I used the narrow (3/4") green tape at the hinges, to close the bag, and, after I closed the lids, all around the case edge to pull the bag tight and away from the lid edge. Advantage: no drilling of hinges, lid inside is protected, and the case forms a pedestal to get the lid off the ground/work bench.
Also, masking instead of removing the reflectors and decals worked very well.

As mentioned, these cans give a very fine spray. If I had stuck religiously to just two passes everywhere and then five minutes break (maybe while doing the other lid at the same time), the result would have been even better. As is I got impatient towards the end of the second case lid, and ended up with thicker layers and two spots of running paint.
Also, the left lid apparently had some scratches that I hadn't noticed before, but which are visible under the yellow paint if you look closely. I'm still very happy with my decision to preserve the original dimpled surface structure of the case lids, but if there is any amount of scratching then more sanding is necessary.
I simply scuffed the surface a bit with 400 grit and a kitchen sponge, and then used the prep solvent (very nice to work with, and not too smelly) and the plastic adhesion promoter.


Bill of materials:
I used two 12oz cans of base coat paint (bought three), each $20; with primer one should get away with less.
3/4 inch masking tape $2.60
prep solvent $2.76 (small, pump spray bottle, very nice to work with)
plastic adhesion promoter $7.95 (seems to do its job)
high gloss clear coat $7.95 (hard to judge the layer thickness that one really needs; in the end I sprayed thicker layers and got a smooth glossy surface)
tack cloth $1.48 (doesn't really do much good except making your hands or gloves sticky)
In total I spent about 100 bucks, divided in two orders (ran out of base coat, ordered two more cans.)
I already had sand paper (400 and 800), nitrile gloves etc..
With primer one should be able to get away with 80 bucks for two case lids.
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Old 11-30-2011, 08:22 PM   #8
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Part of the problem with the yellow base coat not going as far is the opacity of the colour. The yellow pigments are man made and cover far poorer than naturally occurring pigments, so you use more to get the proper colour coverage or opacity. The other variable is the % solids in the can. One product may be low solids/high solvent, the other high solids/low solvent. Higher solids material has more good stuff per can, and will go further than low solids.

The case lids look good. You did a nice job. I've heard of bugs being attracted to the smell of some paints- did the yellow smell appreciably different from the clear?
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