I agree with Brian, the most likely cause of Urethane paint peeling problems is poor preparation of the surface materials. Any oils or residue (even from your fingertips) can screw up the bonding capabilities of the paint.
However, I have seen some paint jobs go bad because the paint shop mixed the wrong primer with the base coat... ie using PPG with Imron or enamel primer with Urethane base coat.
It is interesting to see Brian's note that older Imron catalyst and paint combinations seem to be more durable than the newer Imron formulas. Imron Tech Support (I called them) claims there is no measurable difference in the Hardness and/or durability of the completed paint job.
As far as "curing" the paint when a base coat is applied, you have approximately 24 hours to make any changes to the paint (ie sanding or re-coating or clearcoating with Urethane) before it totally drys on the frame and cannot be changed. Many painters try to speed the curing process a little by using a hot-air hair dryer to somewhat harden the paint, but Brian's suggestion of using a 150 degree oven to complete curing is right on the mark. Tony from Franklin Cycles offered an interesting idea... take the repainted frame and place it in the hot front seat of a abandoned car or truck in the blazing sun. The temp is almost guaranteed to exceed 110 degrees and would easily cure any enamel., laquer ot urethane paint job after several hours!
Regards, Steve Neago "Staring at 2 inches of snow in Cincinnati, OH"
> Mike,
>
> Like I said, paint can be tricky stuff especially on bike frames. There
> are lots of chemical reactions that can produce a multitude of problems.
> I am lucky in that I never learned to paint in the "traditional" way of
> your typical car painter using the guidelines they use; probably save
> lots of trouble by learning to paint bikes from the beginning.
>
> The paint chipping from the under layer is another prep problem most
> likely; but could also be a compatibility or application problem as
> well. Sometimes sanding too smooth is not good for topcoating
> situations; you just have to learn the tricks the hard way.
>
> Not long ago I experienced the first paint failier I have had in 30
> years. For some reason the clearcoat just didn't stick to the color
> coat. The clear began to peel in sheets leaving a perfectly good color
> coat underneith. Never seen this happen before or since; I have to
> assume I did something wrong on that occassion which caused the lack of
> bonding between the color and clear. I had to warrenty the entire paint
> job even though the color was fine; I could not get all of the clear off
> so I just started over. Painful, but one warrenty in 30 years isn't
> enough to get me worrying; I just take an extra step in similar cases to
> insure that there will not be a repeat performance. I actually suspect I
> may have left out one of the components when I mixed that batch of clear
> so I pay extra attention to mixing and won't answer the phone anymore if
> I'm in the middle of mixing paint.
>
> It's really a bummer to get back a fresh (expensive) paint job and have
> the paint jump off like the frame has the plague or something. Bike
> painting is a specialized art and there many ways to go about it and
> hundreds, if not thousands, of combinations of materials to use. My most
> valuable tool is to continue to use what I know works and that I have 30
> years experience using. You end up with very few surprises that way. The
> other best weapon is to hone your skills specifically to produce
> consistant results that give the best performance under the application
> intended. Durability is the number one goal; expert application and
> artistict interpetation are a close second. Obviously a beautiful job is
> of no value unless it stays on a frame as opposed to decorating your
> garage floor.
>
> Gotta paint 3 bikes, better get to it!
>
> Brian Baylis
> La Mesa, CA
> P.S. I'm fine and am making progress towards getting my
> framebuilding/painting duties in balance.
> >
> > rocklube@adnc.com wrote:
> >
> > > Thomas,
> > >
> > > There are lots of ins and outs regarding paints and durability.
> >
> > Hey Brian,
> >
> > How are you? Thanks for the post. I just recently had a local painter
> > respray a Merckx and have not even got the thing assembled yet and it
> > already has a couple of chips:(
> >
> > I think this was due to the adhesion and application method. I had it
> > sprayed with a pearl white with Molteni orange headtube.
> >
> > It look like they primered, then sprayed the orange on the head tube,
> > then masked and sprayed pearl white over the entire bike.
> >
> > The way it chiped at the head tube was that only the pearl white was
> > flaked always revealing orange underneath.
> >
> > Mike Wilkinson