Clear coat help

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#1

Hello everyone. I have a situation that maybe some professionals can shed some light on. For however long I’ve been messing with carbon parts I’ve been shooting clear coat on top. I never had an issue when I overlay a part and clear on top and it only seems to happen when I clear coat on top of sanded raw carbon fiber. I’m trying to figure out why I get what looks like “surface solvent pop”.

Here are my steps
Clean part of frekote 770 and spray glue with acetone
Wet sand part with 320 grit sandpaper
Wash with dawn soap
Clean with acetone again
Let dry
Clear coat with a cheap mini gun and southern polyurethane clear. I typically do 2 wet coats or 2.5 wet with the .5 being a tack coat. I wait between 20-30 minutes between coats and use the correct hardener for the temp outside.

Everything lays down smooth, but as things dry the surface forms very little pin holes on the surface. I say this is solvent being trapped and escaping but it’s at least on the surface and can be wet sanded out where if you have solvent pop you pretty much have to strip the clear off and redo.

I’m trying to avoid wet sanding so that’s why I’m asking you guys. I DO NOT have this issue if I’m overlaying an item and it has some type of epoxy or vinyl Ester resin on top.

I wonder since sometimes I in mold clear with sunshield topcoat if that would work. Does anyone recommend spraying that for a clear coat?

Or does anyone have any suggestions about this? I use adtech 820 with slow hardener. I let the part cure for weeks sometimes before clearing. I use a desiccant snake and also another filter on that.

This issue is very frustrating and the reason I clear afterwards sometimes is that some molds aren’t perfect.

Any suggestions?

#2

In automotive refinishing, usually solvent pop = strip clear coat all the way off.
SPI has a reputation for making a good product. Maybe call them and see what they say. Often you can get the owner of SPI on the phone. The answer may be using a retarder and spraying much lighter coats. Solvent pop most often happens when it is very hot and humid, and also when it is breezy and drying the surface of the clear too fast.

#3

What weather conditions are you spraying in, humidity etc? I occasionally get light pitting in my clear coat that is different to solvent pop, but I’ve only ever had it occur in cooler conditions when moisture is a possibility. I don’t mean cold and raining though, I mean like 18 and partly cloudy.

#4

Yeah I guess I think it’s solvent pop but it’s just on the surface and only occurs hours into curing.

The spraying conditions vary but I would say higher humidity in the 70-80% range. I use a slow hardener already and Spi only has one more that’s considered very slow.

Maybe I’m spraying to close? I am using a pos mini devilbliss detail gun with a small tip but again I use it on painting other things and don’t have this issue. I’ve sprayed Spi clear in even hotter weather and don’t have these issues so I’m certain it’s not the clear it’s mainly from clear coating on top of raw carbon.

Hanaldo. What do you do with the light surface pitting? I think we are experiencing the same thing. Do you just wet sand and clear? Also how many coats do you usually do including if you out a rack coat on?

Also have you ever sprayed sunshield topcoat as the clear or wouldn’t that hold up to well in direct sunlight as a regular automotive clear?

#5

Sunshield topcoat is my primary clear coat, it’s exceptional. Much better than anything else I have used.

I generally just rub the pitting out. Depending how bad it is, I either sand the surface totally flat with 180 grit and reclear, or with minor pitting I wet sand it out with 1200 and then compound.

I do think it is related to the weather conditions, as in perfect weather I have never seen it. I normally do 2 very light mist coats, and then 2 or 3 full wet coats depending on if I will need to sand the surface at all.

Surprisingly,the worst result I have had was when I sprayed on a particularly cool day, around 15 degrees and only beat the rain by 2 hours. I knew they were bad spraying conditions, unfortunately when jobs need to be done they need to be done! So I was using my oven to help things along, setting it to 40 degrees and putting the part in there for 5 minutes between coats. Initially this appeared to work perfectly, when I was finished spraying the part was absolutely stunning. So I put the part in the oven at 25 degrees for an hour before ramping it up to 50 degrees to cure it overnight. When I came back in the morning, the part was covered in the worst surface pitting I have seen. Had to rub it back with 180 and go again, this time with better results.

My conclusion from that is the weather affects things more than expected. I think what was likely happening is solvents were being trapped in the coating, and instead of the oven helping them to escape it was actually making the surface set up too quickly. So by the time I sprayed my final coat, I had a bit of solvent build up in the coating that didn’t present itself immediately due to the outside temperature. Then when placed in the oven, the coating viscosity would have lowered and the solvents would have boiled, causing my issues.

#6

Yeah I hear you about the climate. I think now that you mention you use duratec sunshield as a topcoat. I find that the sunshield topcoat is a little more forgiving then regular automotive clears. I’m just wondering the durability of them is all really and if put out in the sun would they start to fade or peel.

#7

Not that I’ve seen. I’ve got parts that have sat in the Australian sun for 4 years now that are as bright as the day they came out of the mould. Could potentially still happen, but I would have thought that if it were an issue then it would have started to happen by now.

#8

Definitely don’t mean to thread jack, but I’m not sure if we’re experiencing the same thing. Here’s a picture of my result with Sunshield after sanding and polishing. From 10 ft away and at a angle, the piece looks great. If you get close and look straight on though, you see what looks like a textured surface. the surface is actually smooth, and will look like this until I go all the way through the clear to the resin. Is this the same thing? If not, anyone have any ideas? I can’t remember what exactly the spray conditions were, but I let it dry in the sun for weeks before sanding. Thanks!

#9

Can you wet sand and polish it?

#10

That just looks like you haven’t built up a thick enough coat to me.

#11

This IS after it’s wet sanded and polished. It’s weird because sanding down doesn’t do anything. It’s like, inside the clear coat. When I look very closely, it’s like extremely small circle marks or super short hairs. If you look at it 10 feet away when it’s laying down, it looks great. Great reflection of the sky, and you think, great piece. Only when you try to look at it like you’re looking in a mirror do you see the problem.

Hanaldo, could you explain your reasoning on what you see? My process was one flash coat, wait 4 minutes, one heavy coat, wait four minutes, one heavy coat.

Thanks everyone.

#12

I think it is perhaps just the photo then, as from what I can see that appears similar to my parts after I do the first coat.

Could you take a picture of it with some reflection so I can see the surface more than the weave?

#13

How old is the sunshield? How long has it been open for? The styrene evaporates quickly which can thicken the duratec, which can then trapping more air and defects. You can add duratec thinner to thin it out, which helps a lot. Not sure if it will help with your gloss level, but I think its worth trying.

#14

Here’s a couple more on an angle. Unless it’s reflecting off a light, it’s difficult to see what’s going on. The Sunshield probably sat for a couple months before using in a cool garage, but this was piece was sprayed within a couple of weeks of it being opened. I wish I could take a super zoomed picture, but I don’t think I have a camera capable of it.

#15

are you using a foam pad or wool pad to polish? Some times foam pads can get the surface too hot from friction

#16

I’m using a harbor freight cutting foam pad, but the polisher is set to low speed.

#17

Is the laminate well cured? epoxy laminate, or PE/VE?

#18

I use East Coast Resin epoxy. I’m sure it was dry before I cleared. I’m not sure what to think. I have a 2k spray can clear I might try this weekend on a different piece.

#19

That’s very very odd looking.

You say it’s gloss smooth? I’m wondering if maybe the surface wasn’t perfectly smooth?

I’ve used sunshield that was sitting outside and has been open for months without issues.

#20

Awesome info. I’m going to try it out in the next few days

I guess one last question is can I spray this on top of automotive clear?