My first burn through clear

MikeS

MikeS

Camaro Nut
This is my first encounter with a wet sanding burn through the base I'm dealing with. I did a search and several threads are mentioned how to deal with this but may are from 2011 so I wanted to see if the process changed much with the SPI blending solvents.
About the panel: it's a hood and this area is in a very visible part so the repair needs to be as perfect as it can get. It has 3 coats of PPG DBC butternut yellow base that has been activated. Followed up with 5 wet coats of SPI universal clear with 10% retarder added to 4 out of 5 coats. The base/clear is about a month old and has been curing in my garage at 80 degrees average. I blocked dry the clear with P400 initially to level (reduce chances of urethane wave) followed up with P800 wet then P1500 wet. I broke my own rule and was speaking to someone on the phone when I was attempting to wet sand out a spec with P1500 and went through the clear and base and into the sealer. The exposed area is approximately 1/4".
My idea to fix it was to sand the surrounding area with P800 (unless P1500 will provide adhesion?) then mist in some activated base with a touch-up gun, followed by a few coats of universal clear and with a separate gun spray SPI blending solvent as per the tech manual between each coat. Afterwards I would wet sand the repaired area with P1500 to match the surrounding hood area and continue with P2500, then 3000 & 5000 Triazact disks and then polish & glaze. This is the same process for the others panels that are now completed.
Do this method seem sound?

Thank You,
Mike
 
A clear blend in a hood is probably the most difficult place to do it. panels that have been sanded flat like yours is even more difficult. I would at this point just scuff the whole hood, spot my base in, and re clear the whole hood.
 
dmattingly;n85279 said:
A clear blend in a hood is probably the most difficult place to do it. panels that have been sanded flat like yours is even more difficult. I would at this point just scuff the whole hood, spot my base in, and re clear the whole hood.
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Doing that without repriming might result in a bullseye (ring) where the edge of the burn thru is, I would sand the entire hood again and spot prime the affected area let that dry good to seal the rings edge down then sand and redo the hood. If you used the same process throughout the entire project I would be worried about how thin the clear is on the other parts, thin clear is not good.
 
DATEC I agree. When I posted I didn't pay attention to where he sanded all the way to sealer. I was thinking just sanded thru the clear, but with the base sanded thru it definitely needs primer.
 
OMG.....All this for a 1/4" spot that is just down to sealer? Gesh......I may go back to SS if this is what working with BC/CC is like. I was hoping the blending solvent would blend the repaired area in. If not then what's the purpose of a blending solvent? Now I know for my next car restore I will definitely be going back to SS. :)
As for remaining thickness after polishing, it is averaging between 2.5-3.5 mils using before and after measurements with the thickness meter on designated spots. The 5 coats were very wet and each with an 80% overlap. The retarder made the clear flow out pretty flat so it took little blocking with P400 dry to level. Just this one spot on the hood is my fault being I wasn't paying attention while I was talking on the phone.

Mike
 
I'm sorry but the same reaction could happen with SS and to go thru all the hard work you have done I would not want to see you blend the hood (no way, no how if mine but that is just me). You are always better off having a sealed paint panel, meaning no blend spots. In time the blend will show, that will always be your jobs week spot on the paint side.

You will feel better once you fix it right like it never happened and I'll be proud of you too ;), for what ever that is worth.

Just to make sure you understand you can blend the base but clear the whole panel.
 
You're probably right.....I've come this far so no cutting corners now. I looked over the hood and figured at this stage I may as well just block it with P600 to get rid of the P1500 cut it is at now to ensure better adhesion. Mist in some primer surfacer then catalyzed base and once dried just flow coat it. I figured with the blocked flat clear as a foundation the new clear should flow out nicely especially if I add some retarder. I'll shoot 3 coats then when cured after a week or so work it up with P1000, P2000, 3000 and 5000 Trizact then polish. I'm sure glad I didn't take down the temporary paint booth.

Thanks for the input!
Mike
 
As a follow up to my going back to SS comment, one reason is because if while color sanding I see a spec (typically it looks like one very tiny grain of pepper) in the paint, at least it's on the surface and can easily be removed whereas with BC/CC, you don't know where the spec is. It can be on the base surface below all the clear layers, or within the clear layers. One thing I have learned while working with BC/CC is that the darker the spec is, the closer to the surface it is so it can be removed relatively easy. Dimmer, and it is very likely well into the paint layers and you can only hope that while trying to wet sand it out that you don't go too far and risk clear burn through. Now, on a dark color car it's likely not noticeable, but on a very light color it is very noticeable. I don't know...is seeing a lone spec something to live with with a light color BC/CC job? Maybe I'm just being too critical on myself. I've heard people have one or two in their fresh jobs from production shops.
OK.....sorry for the long reply....back to a coffee :)

Mike
 
that spec you are talking about is what can make a white job a nightmare. those that say white is easy really don't know any better. Yes white for body work makes life easier on that side of the job, but when I do any car and when I am teaching someone I always say treat it as though it is black going on. on the paint side white is and can be a real hair puller you go blind from the light and sometimes loose track of where you are in the passes while spraying body and head movement helps. A speck of anything other then white will show and here goes your hair in big clumps sometimes. when I make each pass and while waiting for it to flash I look hard for anything, it can get stressful but make it a habit. That way hopefully you will be able to pull it out with a piece of clean tape. Don't worry about the little mark left behind it will either flow out with the next coat or be buffed out when completed I also remember where I did it and will give it a little extra coat in that area first and let it flash before starting the next coat.
 
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