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Getting a durable finish

Old 05-20-12, 01:08 PM
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Getting a durable finish

I have always heard that home-made paint jobs are not as durable as professional finishes, and sure enough, the two frames I have painted look very nice but chip easily. What makes the difference? As far as I can tell, I can do exactly the same prep work, and use the same paint and painting techniques as anyone else. One thing I did not do was to bake the frames afterwards, but supposedly the paint hardens just as well with time. What do the proís do that I canít? And how can I come as close as possible to achieving a professional finish with a DIY job?
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Old 05-20-12, 07:37 PM
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What materials are you using?
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Old 05-20-12, 08:15 PM
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kroozer- Part of the short answer is that the chemical make up of the paints that are easily applied (and actually bought in the first place) are for the cost of purchase and application ease. Not durability. The primer's abuility to adhere to the base metal, the paint's ability to do the same to the primer (and any sealer layer between), any modifing additives (reducer/accelerator) the resulting thickness of the finish and lastly the hardness of said finish are all a factor. While you didn't say what kind of paint you've used canned package paint is at best a cheap compromise. Andy.
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Old 05-20-12, 08:33 PM
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I used different materials each time, but it both cases it was high quality automotive paint and primer, applied with a spraygun. I removed most of the old paint chemically, and finished with and old knife and sandpaper. The first frame was primed with zinc chromate since it had some chrome plating. The main base color was Dupont Chromabase metallic blue, and I finished with several clearcoats. I don't remember the materials I used on the second frame. It was a different primer and base, but still good quality materials from the same store. I painted it in the autobody shop of a friend.
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Old 05-20-12, 09:24 PM
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kroozer- Two different data points make a hard start. The painters that i've talked with have used a single system for a number of pieces before they begin to understand the range and variabilities involved with that system. I'm no painter but do unserstand that it's a very complex arena. So i'll see what the experts can offer. Andy.
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Old 05-20-12, 11:07 PM
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I appreciate your points, Andy. It sounds like you're suggesting that it is indeed possible to get a good, solid, durable finish using the paint I used, but it's mostly a matter of refining techniques, mixes, timing, etc. My problem is that, even if I was using a single system, I paint a frame maybe once a year or so, not nearly enough to effectively refine a system. The finish on the first frame turned out OK (though not great) as far as durability goes, but the second one is unacceptable, to the point where I'm considering stripping it and doing it over. It looks beautiful but it just chips and scratches way too easily. I took my time with it and tried to do everything right, used good materials, and had my friend at the autobody shop checking things out from time to time. I put down 2 coats of primer, 2 of base, and 2 clearcoats. Plus the contrasting color and detail work (outlining lugs, etc.). Maybe I should have just used more paint, I don't know. Now I have another frame that needs to be painted, and I'm thinking of brush painting it with Chromabase.
Cheers,
George
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Old 05-21-12, 06:58 AM
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George- When i first started to build i did my painting. WE used Imron as it was the cool stuff at that time. While my paint work was acceptable I was never comfy with it. Like you I didn't paint enough to get a good feel for it. This and the hassle to establish a painting set up made me go to real painters. And I have tried a lot over the years! About 7 years ago I rau across Doug Fattic and won't go elsewhere unless he were to retire. A true master with a paint gun, has a great eye for color and is a nice guy too. He's the one who convinced me that as a builder my personal frames were the most importnt to look good. Most lay people judge the frame by it's cover. Andy.
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Old 05-21-12, 11:37 AM
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On my last paint job I used automotive paint from Sherman Williams. The primer is amazing. Its their epoxy based primer intended to be used on heavy duty vehicles like dump trucks. I havent had a scratch yet that has penetrated the primer. The paint on the other hand has chipped and scratched fairly easily. I believe this has to do with commercial frames being baked. I also was in a time/weather/temperature crunch and rushed the clear coat. I only applied 4 light coats. 10 coats (or fewer heavier coats) might make it more durable. That said, the finish was excellent.


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Old 05-21-12, 11:56 AM
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the people I know that paint frames say that baking promotes drying, but does not promote durability.
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Old 05-21-12, 12:15 PM
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There are UV curing paints, putting them under UV lights has effect.
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Old 05-21-12, 02:20 PM
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Any idea how strong the UV lights have to be?
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Old 05-21-12, 02:29 PM
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my expericnes is limited.... but the frame I painted with auto paint has had pretty durable paint, the paing with rattle cans not durable at al.

this is what i did (after much reasearch on forums)

stripped frame chemically and then used scotchbrite pad

gloves on

clean frame with acetone

used acid etch primer

dried to recoate time

used high build up primer

light sand

used 3-4 thin coast color using a preval (forget paint brand, but is was automotive, hit it with reducer and start painting) I allowe enought time so that I could get all the coats on as soon as recoat dry time was complete.

then 4-5 coasts of cataliyzed clear... again careful with recoat times.

this is on my son's fixie.....so far very durable. One big chip but that was not a paint failure.

overall i think bike paint gets much more abused thad does car paint...so it could the there needs to be lower expectations as to bike paint durability?
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Old 05-21-12, 07:45 PM
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Originally Posted by unterhausen View Post
the people I know that paint frames say that baking promotes drying, but does not promote durability.
Unterhausen is right. Even after baking a frame can take months to completely gas off.
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Old 05-21-12, 08:17 PM
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Acetone is good for cleaning stuff off, but isn't always clean itself. Some of it contain sufficient trace amounts of oil that it is not actually clean. I have lots around for composite stuff, so I use it. But I always follow up with alcohol. And where possible just use the alcohol. I wonder if there is a clean brand, or medical, or something.
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Old 05-22-12, 12:05 AM
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Forget chemical stripper, just get it sandblasted. Its pretty cheap if you go to a general place. Like $30. And you won't risk lung damage.
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Old 05-22-12, 04:47 AM
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Originally Posted by MassiveD View Post
Acetone is good for cleaning stuff off, but isn't always clean itself. Some of it contain sufficient trace amounts of oil that it is not actually clean. I have lots around for composite stuff, so I use it. But I always follow up with alcohol. And where possible just use the alcohol. I wonder if there is a clean brand, or medical, or something.
The paint manufacturers have a product for this. Ask your jobber. A good prep is both chemical and mechanical.
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Old 05-22-12, 07:00 AM
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Manufacturers first priority in designing professional car paint isn't durability. They know auto body guys want to get a good look on as fast (and cheap) as possible. Ease of use and the speed it can be applied are what makes paint sell so a job can be profitable. The car is not likely to be in the owner's possession long enough for him to come back and complain. Bike paint jobs (as mentioned) take a greater beating and require the most durable kinds. In my experience, a base coat/clear coat system (when the color coats are very thin and need to be protected by clear top coats) are not as durable as a polyurethane enamel like Dupont Imron (although I use both).

There are all sorts of factors that contribute to paint problems once the best ones have been selected (and the worst ones avoided). Of critical importance is the amount of time that has elapsed between coat applications (which very depending on temperature and humidity). And of course you have to usually pick reducers that are matched to the temperature when spraying (and one can't spray when it is too cold). If too much time has gone by the top coat won't bond with what is underneath. The best show quality paint jobs require lots of sanding between primers and color coats and clears. This can lead to contamination that keeps later coats from sticking as well. I use cleaners that paint companies design for this purpose.

Over the years I've discovered what types of paint are the most durable for each layer (primer, clear coat, etc.) and will sometimes intermix products from different companies to get the best results. I also often use a sealer paint between the primer and the color. This increased the bond between the two and provides an even undercoat color for greater top coat consistency and clarity.

And by the way - as has already been said - baking a frame does not increase its durability. The general description of painting steps I hand out to my framebuilding class students is one full page but the instruction sheets for my painting class students are pages long. Of the 3 primary skills used in making a frame, brazing, filing and painting, I think painting is the most difficult.
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Old 05-22-12, 08:44 AM
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Dough,
Any suggestion where to find a place that sells Imron? Looking at Dupont's site it mostly lists autocollision centers. Do you still clear coat it?

Any opinion on the previously mentioned UV curing?
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Old 05-22-12, 01:37 PM
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My experience with the topic... hope you continue using car paint as well.

1 if you cant sand blast the frame just use a steel wool to etch it really good so the primer gets a lot of surface to stick really well.

2 use your favorite car primer, the nice about epoxy primer is that covers really well. Since I paint in my backyard i use u-pol high surface primer that is a car professional grade rattle can primer, awesome stuff. Never a single issue with this thing not even peeling on the dropouts that is the usual problem in any paint job.

3 use car paint, since your friend knows about this i wont give you any tip because the paint will come up as good as the painter and the paint is. I have used cheap ass paint and stuff like dupont, nason and sickens for example.

4 clear coat... the clear coat has to be sanded and shot depending on the paint instructions, some paints you have to clear after like 30 mins or 3 hours, with others you can wait 12 hours to do it. In the case you want to clear next day always you can sand with 600 grit wet sand paper and shot the clear over it. I always used 3 coats or 4 because I sand the clear a lot to get rid off of imperfections in the surface and then a super nice polishing.

IMO the results in the finishing will depend of the clear itself and in the how much you sanded and polished the clear coat.

Some clears are really bad and other ones no matter how bad the paint is (if primer is good) the clear will be as hard as a rock and will protect the base color just like in a car; that's the reason I use nason clear coat, If the clear was shot wrongly or the wrong clear coat was used then the rocks and junk will get to the paint and the paint job will nick really easy.

Somebody mentioned about UV protection curing???? 1st time i heard about UV curing.... If the clear doesnt have UV protection the clear will turn yellow after a few months, rattle can clear coat like rustoleum doesnt have UV protection (they have one that does now) and in quality is not neither even close to the hardness of polyurethane clear coats. Rustoleum paint and clear is just junk for a descent and durable bicycle paint job.

The day somebody shows me a paint job like this using rustoleum i might change my mind about that paint.







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Old 05-22-12, 01:46 PM
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Never used that paint but a friend told me is pretty good, that brings me to a basic problem... did you follow the instructions to paint with this paint?

From what I have read, the paint and the clear uses a hardener, if you dont put that the paint will take longer to dry and wont get as hard as it was designed. When you dont use hardener or you are painting in the wrong temperature specially during the winter (i have painted under the snow) you have trick the paint... play with the mix ratios, heat the paint or even heat the frame a tiny bit so the paint sticks how it should be. My fav one is to heat the paint a few degrees so when you spray it it wont hold air humidity and will dry faster.

The only thing I can think of in your problem is that you applied the clear wrong.

Originally Posted by roburrito View Post
On my last paint job I used automotive paint from Sherman Williams. The primer is amazing. Its their epoxy based primer intended to be used on heavy duty vehicles like dump trucks. I havent had a scratch yet that has penetrated the primer. The paint on the other hand has chipped and scratched fairly easily. I believe this has to do with commercial frames being baked. I also was in a time/weather/temperature crunch and rushed the clear coat. I only applied 4 light coats. 10 coats (or fewer heavier coats) might make it more durable. That said, the finish was excellent.

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Old 05-22-12, 02:06 PM
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Temperature played a factor. I was doing it at the end of fall at the very minimum of the temperature range. I guess "chipped and scratched fairly easily" is fairly subjective. This is my commuter and gets regularly raked against other bikes and poles when I lock it up.
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Old 05-22-12, 08:17 PM
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I just stopped by my local paint store and they have Dupont Imron. All else being equal, is this going to provide a more durable finish than other paints? I've always heard really good things about it.
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Old 05-22-12, 08:35 PM
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Everyone using a decent mask to deal with the toxic vapors? 3M has one for about $30-40 that works well from what I've heard.
I don't think you can buy Imron in CA, for quite awhile actually, EPA doesn't like it.

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Old 05-22-12, 09:54 PM
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Here in Mexico we still get all the good stuff.
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Old 05-23-12, 08:33 AM
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Browsing through a car forum there was a post by a Dupont employee. Looks like Imron is a generic label used on a variety of paints now. The reputation for durability came from their industrial strength paint that was maid in the 90s. Now most available-to-consumer "Imron" paint is just generic car paint. They also claimed paint science has come a long way and there is better stuff out there now.
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