Color Differences between coats (single stage)

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PostPosted: Tue Mar 28, 2023 12:32 pm
Hi All,

Newbie here- please go easy on me.

Problem: After three wet coats of single stage paint, wet sanding with 1500, and buffing, I'm getting pretty terrible color variations as I sand through my third coat into my final coat. Pics below- sorry for not embedding the images. I can't for the life of me figure out how to do that from google photos as the links don't seem to work using the IMG code.

Product: PPG Delfleet Essential ESSS Polyurethane Single Stage. 6:1:1 paint, activator, and hardener, with optional recommended reducer. This is a solid color (not a pearl or metallic).

Prep: I mix the paint in the gallon can on a paint shaker for about 5 minutes before every painting batch. Mix the paint and stir thoroughly (3-5 minutes). Strain the paint into the gun. Use the same exact paint in the gun for all three coats.

I've finally figured out how to get the paint to lay down with minimal orange peel and no runs. I'm really not sanding much at all, but there are a few spots where I sand through the last coat into the second coat and in those areas, I'm getting a color differences (stratification lines like a topographical map). It's super hard to pick up on camera after sanding and buffing. I'm sharing two pictures here, each with a version that shows the color lines I'm talking about. It's really obvious in person (and totally unacceptable).

Question: what am I doing wrong? I know I need to repaint to fix this, but after having repainted the vehicle multiple times now, I'm at my wit's end. This thing is gonna get scrapped if I have to redo the paint again.

I can provide tons more info on my process and approach, but didn't' want to make you fine people read a dissertation.

Thank you so much for your help. I'm about to jump off a bridge at this point, after years of restoring this vehicle (1976 toyota landcruiser FJ40, formerly a rust bucket).

https://photos.app.goo.gl/LbgoicmTW4UcHW2r5

https://photos.app.goo.gl/vkAoxvWvCtWP5oCV9

https://photos.app.goo.gl/irgPEs8iraJ9kPvi6

https://photos.app.goo.gl/NgfSC6saVwtTSQEZ6

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PostPosted: Tue Mar 28, 2023 4:34 pm
With your photos, you can upload directly here. When posting a reply, scroll down until you see Options and Upload Attachments tabs. Select Upload Attachments, browse to the picture file and add the file.

I can just see what you're talking about in those Google photos, but it may help if you take some more - from a slightly different angle and lighting. It's very hard to see what's going on in the Google ones.

Usually I can spot problems like this, but this one has me a little stumped. Can you give us some more information on things like room temperature, flash off times, gun used, how long from spraying to sanding and ambient temperatures?
Chris



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PostPosted: Tue Mar 28, 2023 5:15 pm
Thanks for the reply!!! I see the upload option now. I wish I had taken more pictures, but my phone was having so much trouble picking it up.

I've added one additional pic of one of my fenders in daylight. hopefully you can see the color variation a little better there.

First pic- if you look closely in the reflection of the towel I'm holding, you can see the meandering line where the color changes.

PXL_20230326_213103841.jpg


Same pic, but with a red line drawn to show you what I'm talking about:

Pic 2 with line.jpg


Same deal here, but on another panel. First pic is without my red line showing you where to look. Second has the red line drawn on to show you where the issue is. Sorry it's so hard to see.

PXL_20230326_213113725.jpg


Pic 1 with line.jpg


Here's a picture of a fender out in daylight. If you look in the area where you can see the reflection of my phone, you'll see a dark wavy line.

PXL_20230326_210205058.PORTRAIT.jpg


Unfortunately these are all the pictures I have at the moment.
Last edited by pierps on Tue Mar 28, 2023 5:28 pm, edited 1 time in total.



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PostPosted: Tue Mar 28, 2023 5:24 pm
Regarding additional details:

I'm using the standard activator (ESX510, for 60-68 degrees F). My booth is a makeshift plastic sheeting booth that is fairly well sealed, in my heated and insulated garage. Two big HEPA filter/ blower units pushing heated air into the booth, causing positive pressure, exhausting out of a few smaller openings to the outdoors through the garage door.

I'm heating the shop to 70 degrees, and getting 50% relative humidity. I check the paint and the parts with an infrared thermometer to ensure they are also at around 70 degrees. I know this is slightly over the top end of the range for the activator, but when I open the garage door while painting and flashing, the temp does drop to the mid 60's.

I'm applying three fairly heavy/wet coats. Recommended flash time is 10 minutes, but Ive been waiting 15-20 minutes between coats to avoid solvent pop.

Gun is a Devlibiss GPG2. Kind of a middle-of-the-road gun. 1.3 MM tip. 22-25 PSI.

I'm meticulous about the prep, I'm shaking the paint with a paint shaker, and stirring the mixture very thoroughly. Using the same paint for all three coats- all poured into the cup of the gun at the same time. literally the same paint.

What I've wondered is whether I'm putting the paint on too think, causing the pigments to settle into the bottom the wet coat, causing that dark dividing line in my pic as I sand down. That, or during the 15-20 minutes of waiting between coats, the pigment is settling in the cup of the gun and needs to be re-stirred?

After posting this, I got in touch with a body shop I'm considering having take the paint work over for me. The guy has 45 years of experience, and lots of experience with single stage. I told him my predicament, and he said "oh, yeah that always happens when you sand through coats of single stage. you're changing the color of the paint as you sand". I'm not exactly sure what he meant, but he told me that with single stage, you have to be extremely careful when wet sanding, to not go through your outer layer or this will happen nearly every time... which is just lovely.

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PostPosted: Tue Mar 28, 2023 6:43 pm
Thanks for the extra info. Sounds like temps and activator are pretty good.

Flash times sound ok, but are a bit dependent on how thick you're laying each coat on. Like you, I suspect this may have something to do with it, but in all the years I've been painting I've never had this happen, unless I used a different mix of paint. As for pigment settling, no, not in a solid colour although it can certainly happen with a metallic.

If I look at the photos I think I can see a colour difference between the top of the last coat and where you broke through. Being darker is, clearly, more evident where one can see the feathered edge and this makes me think that it may have been put on too heavy and hasn't properly flashed off/cured.

Beyond that I'm scratching my head. Maybe some of the other guys can offer more.
Chris



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PostPosted: Tue Mar 28, 2023 6:58 pm
it sounds like you did everything right. and can't see why this happened. and i can't see getting a different shade from sanding through a 3rd coat of S/S, UNLESS after you sanded through the 3rd coat and some of the second the paint film thinned out and if there is a light colored sealer or primer under this, this COULD be the problem.
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PostPosted: Wed Mar 29, 2023 6:40 am
Looks to me like the coats of paint did not fully melt into each other. So, when you sanded and buffed, you sanded off one layer, and the division line between the 2nd and 3rd layer is visible, not so much a color change.
Similar to when trying to do a blend on older paint, and it doesn't melt in completely.

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PostPosted: Wed Mar 29, 2023 8:44 am
chopolds wrote:Looks to me like the coats of paint did not fully melt into each other. So, when you sanded and buffed, you sanded off one layer, and the division line between the 2nd and 3rd layer is visible, not so much a color change.
Similar to when trying to do a blend on older paint, and it doesn't melt in completely.


This was my thinking as well. It looks like the edge of a top coat on a blend or possibly a coat that wasn't applied all the way to the end of the panel. Seeing it is on both sides at about the same position.
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PostPosted: Wed Mar 29, 2023 10:05 am
Thanks so much for all of the replies!!

I know my pictures aren't super great... but one thing I've been thinking that I didn't say in prior posts, which some of you have noticed, is that the dividing line where I cut down into the next coat is where the color difference is most severe. Staring at the panels in person, it's REALLY hard to perceive a color difference in the areas on either side of the dividing line.

So it sounds like the group is aligning around the idea that the coats didn't meld together, and that maybe it's because I put it on too thick and/or didn't allow enough flash time?

A few follow-up thoughts:

PPG says the recoat window is 10 minutes to 72 hours. So aside from taking longer, what's the downside of waiting, say, an 30-45 min between coats to make sure it flashes off correctly? The pot life is only 2 hours, so if I'm doing three coats, i need to be mindful of that.

And I suppose I need to get one of those paint mil gauges, spray on a test panel, and make sure I'm not putting the coats on too heavy?

PPG also recommends 2 coats with 10 minutes of flash time. I put on three heavy coats thinking it would give me plenty of margin for error for cutting and buffing. But is it possible that somehow putting down more coats than recommended is the issue?

One more tidbit is that I'm thinning the paint using PPG's recommended reducer (ESR300). They say not to thin beyond 10%... After all the trial and error, I concluded that I needed to go somewhere closer to 20% to have any chance of limiting orange peel. Could using too much reducer cause issues of the coats not melding together?

Thanks for all the support! I'm glad I joined this forum!

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PostPosted: Wed Mar 29, 2023 3:27 pm
pierps wrote:what's the downside of waiting, say, an 30-45 min between coats to make sure it flashes off correctly?


No downside at all, other than, as you say, the extra time and need to watch pot life.

pierps wrote: I need to get one of those paint mil gauges, spray on a test panel, and make sure I'm not putting the coats on too heavy?


This is a really good idea, albeit that it does involve some cost. You'll be surprised at how much paint you don't need to put on.

pierps wrote:the group is aligning around the idea that the coats didn't meld together, and that maybe it's because I put it on too thick and/or didn't allow enough flash time?


I can't see how the first could happen, but certainly the last two.

pierps wrote:After all the trial and error, I concluded that I needed to go somewhere closer to 20% to have any chance of limiting orange peel. Could using too much reducer cause issues of the coats not melding together?


No, more likely the opposite. And it's not like you're over reducing by a huge margin. 10-20% is fairly normal. As for the orange peel, that's really a technique thing. Light coats will actually result in less orange peel than heavy coats, as will slightly higher inlet pressures - IIRC you were at 22-25psi where I'd probably be between 28-32psi, depending on gun and air cap.
Chris
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