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Old 04-11-2015, 12:57 PM   #1
stephano OP
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Best way to paint plastics?

I'm fixing some scratches and blemishes on my LC4 and I've heard of people painting the tank. I'm going to be painting a couple other plastic things on it too but in saying that, I'm really trying to find out whats the best type of plastic paints (in an average level of affordability) and/or the best method to go about painting plastic so it comes out affordable and nice looking.

I tried to seek the advice of a paint store but by the time the guys done talking I'm already looking at a fortune. Then again, I'm sure the simple $5 can of Kyrlon plastic paint isnt going to be all that great either.

Hopefully some of you have some insight on this. Thanks.
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Old 04-11-2015, 01:47 PM   #2
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I've had two issues with spraying plastics in the past - adhesion failure and cracking of paint, both when using automotive body paint. What the panel is made of makes a huge difference.

To get decent adhesion you need good plastic primer, especially on panels made of polypropylene (many car bumpers etc) since it has a low surface energy. Over the primer, any paint you use must be sprayed as thinly as you can or it might lift. High-build paints will lift easily when the plastics flex. Commercially plasma/flame surface activation also improves adhesion, but it's not suitable for the home tinkerer.

The cracking problem happens when you have very deeply scratched or cracked and patched panels, especially if you use a filler for the cracks. The high solvent percentage of traditional 1-K paints gets absorbed by the plastic, especially at the scratch/crack and causes uneven drying of the paint, which cracks. I've seen this on painted ABS, no idea what other plastics do. The way I solved it was by putting on a thin layer of glass fiber. Yes, very nasty!

On fresh, undamaged panels it's much easier.

What equipment are you set up with? If you don't have an air spraying setup don't exclude rattlecans outright. I've had some luck with doing a couple of mudguards (polypropylene) with the Plasti-Kote brand (never seen a can of Krylon - not even sure if we get it in the EU?).
The trick with rattlecans is to use very thin coats, just enough to provide coverage, and NO MORE, letting it dry and then giving another coat as required. Don't try to build up thickness or you will get runs. The last coat should have full coverage to avoid inconsistent finish while with the first coats you don't need that much.
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Old 04-11-2015, 05:10 PM   #3
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Thank you.

Currently my only means is rattle cans. No air sprayer. What I'm doing is filling in some minor scratch/gouges left from someone laying my bike down on gravel. Luckily not going very fast.

The fill material I was sold (after LONG exhaust explanations of what I'm doing with the paint people) was something called icing gold. I dont plan on using much but ya know how it goes, and by the time I'm done the 1/2" area will have a film of material 2" round. I was told that I dont "need" to prime the tank since the adhesion should be fine as long as I have it completely free of oil's and the surface isnt high gloss. I guess there's no harm in still priming it.....

The paint they have, I cant remember the name of the product but its a very expensive spray can specifically for painting automotive interiors like dashes and even fabric or leather. Its supposedly a very thin material and will bond deeper with the plastic on a molecular level whereas most other stuff sits on the surface or is more "plastic" like. At least this is what I'm being told, which is why I'm asking before I go through with this.

They keep trying to sell me on going the automotive paint route with two part catalysts so I wont have trouble with spilled gas affecting the paint but cripes.....by the time I was done, I could have just replaced the tank. This HAS to be affordable.
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Old 04-11-2015, 05:30 PM   #4
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Look at duplicolor rattle can from the auto parts stores.

Prep the plastic; clean, sand, scuff and WASH with a good detergent like Dawn liquid, then dry thoroughly. You should finish sanding with WET 2000 grit paper. Very wet 2000 grit paper. That way your painting does not have to cover and build the scratch marks.

Coat the piece with adhesion promoter, following directions as to coating and time set before painting, and max allowable time to paint.

Pick the color of your choice and apply a light coat, almost a mist. Recoat in 10-15 minutes giving the paint time to flash, with a second coating, heavier than the first but not the final result.
Again, 10-15 minute wait time then a third, final heavier coat. Now you should have the color you want.
You can allow 20-30 minutes or so then clear coat with a spray can. Let dry 15 minutes and if the result does not have the depth you would like, sand with 2000 grit paper, wetted with soapy water. Sand lightly and be generous with the soapy water.
Rinse, dry, then apply another coat of clear. Let that dry and check the result. Should be pretty good and your paint job will have some flex to it, and be properly bonded to the material surface.
Works for me anyway,. Good luck
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Old 04-11-2015, 07:41 PM   #5
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I used some 2 part automotive paint i got from thecoatingstore.com, the paint is made by urekhem. I used their primer , color and clear on the plastic aside covers, rear fender, fiberglass front fender, and steel gas tank. It's been six months and still looks great with no problems. I sprayed everything with an old Binks 115 touch up gun and a crappy under powered compressor.
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Old 04-11-2015, 10:19 PM   #6
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Paint abs is pretty easy for polypropylene or polyethylene it's near impossible to get paint to stick.

I have flame treated small PE parts and have been able to paint them and the paint even stuck ok.

I used rustolym satin black before the formula change in the mid aughts and it held up ok on my XR650L.

I doubt the new formula paint would work as well.
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Old 04-12-2015, 06:33 AM   #7
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Quote:
Originally Posted by squish View Post
I have flame treated small PE parts and have been able to paint them and the paint even stuck ok.
Any more detail about how you did the flame treatment? Did you use a reducing or a oxidising flame?
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Old 04-12-2015, 06:54 AM   #8
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I painted my belly pan with the Krylon. Looks good and stuck on for sure. But I wouldn't use a rattlecan on a tank.....hard to do light coats especially the Krylon. And took a long time to cure/harden completely. That is I wouldn't think it could be totally fuel proof for a good long while.

PE plastics? I'll go try some of that in a few minutes with the Krylon plastic paint. I bought a large sheet of "high impact PE", I also need to know how well paint would adhere to it.I haven't looked at my test piece for a while, the one where I adhered bedliner to BMW PE plastic without too much prep but a good wash with Naphtha to remove the sillycone/waxes.

To be used before and after sanding them waxes/sillycones removers, you do not want to sand any of that into the surfaces. Will cause fisheyes and them are extremely hard to fix later. Dedicated products for that, such as Rusto "tar & wax" remover are just that, rebadged Nahphta/Camping fuel/lighter fuel etc...etc...! Much cheaper by the gallon at Ace.

Honda plastics? The XR650L white stuff is marked PP. Me not like the white or the scratches from the PO. I have enough Krylon to do that but too large of a surface for nice even coats. Punch can to release the propellant. Dump paint in container....reduce if required and then use the paint gun.

Of course....outside temps and relative humidity considerations will have to apply. And by then the bugs will be out, will have to set up my screen tent to control them and the dust.
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Old 04-21-2015, 09:44 PM   #9
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Originally Posted by gzr View Post
Any more detail about how you did the flame treatment? Did you use a reducing or a oxidising flame?
mapp gas torch with a wide flame spreader

You run the flame over the plastic until you see it flash.

Once it flashes get the paint on quickly, It takes practice.
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Old 04-23-2015, 10:44 AM   #10
MrPulldown
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I have had good luck with Krylon Fusion paint. Not sure about a plastic gas tank. Don't they out gas. All the DR350 guys end up with paint and decals that bubble.
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