Clearcoating Painted Props.

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SuperSpark

New Member
Would appreciate some advice.

I printed several duplicates of a mini 3D Printed prop I designed. So far, I've resin coated and hand-painted 3 of them.

The first was painted with tamiya acrylic paints. For many reasons, this was a bad idea and I was told why later. However, I got it done and clear coated it with some Krylon Clear Coat spray to protect the prop and... Something weird happened.

I clear coated it, but it was like the paint was getting cooked and melting off it. I used a foam brush to clear out a glob of clear coat out of one area and the paint job, which had been done for several days, just melted right off where the brush was. Furthermore, because I would clear coat one side at one point and the other side the next day when it dried, I noticed that the melted paint pooled around the bottom, somewhat sticking it to its bed at parts and bleeding the melting paint into parts of the opposite side, which then forced me to paint it over and clear coat again. Clear coating the other side had the same problem, though it was tolerable due to one side only having one color.

For the second one, I someone recommend me Vallejo paints, so I only used Vallejo paint in my desired colours instead. Much easier to paint with. I also used a different clear coat spray by Tamiya, as it said it was specifically for plastics. I sprayed the backside first since it was a single color and... Same problem. The paint melted over and ruined part of the paint job on the opposite side. I've since repaired the paint job and painted the 3rd print... But now what?

My prop is painted with black, white, and metallic silver paints, both in tamiya and vellejo brands. Recently, I was told that metallic paint have all sorts of odd melty reactions with most clear coats, so this is also a possible factor, though I don't quite understand why.

Last time I painted and coated a 3d printed print prop I made was several years ago, but detailing didn't matter because it was spraypainted one color and the paint never seemed to melt off like that when I sprayed that same Krylon clear coat. There is actual detail on this print and because of that, I've had to repaint these, the first one especially, several times. I'm not very knowledgeable with paints and a bit afraid of continuing to clear coat them without understanding what's going on. I don't want to have to fight with repainting this again.

Why is the dry paint is melting off the print from the clear coat? What can I do to stop it? How can I seal it?
 
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renaissance_man

Sr Member
RPF PREMIUM MEMBER
Have you given the paint plenty of time to cure, at least 48 hours, maybe even 72 hours prior to clear coating.
Also it is best to stick with the same brands when clear coating.
Having said that I've used Mr Hobby semi-gloss and gloss clearcoat on Halfords spraycan automotive paints and tamiya spraycan paints.

Make sure the paint has cured, the air is warm and not humid and do a test piece prior to committing to painting the final prop.
 

SuperSpark

New Member
Have you given the paint plenty of time to cure, at least 48 hours, maybe even 72 hours prior to clear coating.
Also it is best to stick with the same brands when clear coating.
Having said that I've used Mr Hobby semi-gloss and gloss clearcoat on Halfords spraycan automotive paints and tamiya spraycan paints.

Make sure the paint has cured, the air is warm and not humid and do a test piece prior to committing to painting the final prop.
In each case so far, I've given the paint several days to dry. I believe the last time was like almost a week. At this time, I haven't touched it since early Saturday morning and that was only for minor touch ups since most of the painting was finished now over a week ago. Right now the first 2 are the test pieces. My 3rd one is the best one, so I'd like to figure out what's going on here and why this is happening first.

So environment is a factor in this? I'm doing the clear coating in my garage which I guess average temperature or slightly lower. I could do it on my balcony so it's outside but that's right beside the air condition unit, which I'd rather not risk having the fumes sucked into. Might it do better to put it by a heater while it dries?
 

Rogviler

Well-Known Member
I've used all of those combos and not had anything like the reaction you describe. The closest would be when I used a Krylon lacquer clear too heavily and it started to wrinkle the paint slightly in a few areas, but that's pretty mild compared to what you're describing...

So I would 100% suspect the substrate causing a reaction to the clear. What are they printed in and what is the resin that you coated them with? You can get all sorts of reactions between different types of plastic and paint, the most notorious example being vinyl and nylon reacting with enamel paints to create a sticky mess that never dries. So that would be my guess.
 

renaissance_man

Sr Member
RPF PREMIUM MEMBER
Make sure both the prop and can or clearcoat are at least at room temperature. Avoid moisture in the air, try again on a warm dry day.
Painting and clearcoating can be a pain. I sympathise with your trouble here.
As the Rogviler said, avoid enamel paints.
 

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SuperSpark

New Member
I've used all of those combos and not had anything like the reaction you describe. The closest would be when I used a Krylon lacquer clear too heavily and it started to wrinkle the paint slightly in a few areas, but that's pretty mild compared to what you're describing...

So I would 100% suspect the substrate causing a reaction to the clear. What are they printed in and what is the resin that you coated them with? You can get all sorts of reactions between different types of plastic and paint, the most notorious example being vinyl and nylon reacting with enamel paints to create a sticky mess that never dries. So that would be my guess.
The object was printed in PLA plastic. I resin coated it with XTC-3D. The last prop project I painted was my Millennium Puzzle, which I printed in PLA, resin-coated, primed, spray painted gold, then clear coated. I don't remember it having any such sort of reaction when I sealed it with the same Krylon clear coat, so I'm very confused. My friend taught me this same method that he uses to finish his prints and even he's baffled. This is the first time I'm sealing something hand-painted.

Random thought but could it be I'm spraying too close to the object? I know it says to keep some distance but maybe it's not enough?
 

SuperSpark

New Member
Wanted to provide a little more context to see if maybe that makes it easier to solve.
IMG_4465.JPG

These are my Wonder Pendants based on The Wonderful 101 Video Game. I designed them myself from scratch, including the original 3D Model and 3D Printed many of them in PLA, later resin coating them in XTC-3D. These are my 2nd and 3rd painted ones, which I primed and painted around a month after coating them. The first painted one (not pictured and made with Tamiya paints) is 'finished' but with some imperfections for various reasons including what I pointed out in the original post. These ones were painted with Vallejo paint. The smaller one on the right here has been clear coated on the back.
IMG_4463.JPG

When I clear coated the back of the smaller one, it created this mess. The silver paint melted into a puddle and I had to move around to make sure it didn't stick to the cardboard and potentially flood the opposite side. That is what happened with the first one with Tamiya paint using Krylon Clear Coat. However, on this one, I used Tamiya Clear coat in hopes it wouldn't turn out that bad again and it did. I'd like to figure out what's happening before attempting the bigger one.

These are the Clear Coats I have. Recently someone told me that at least one of them might be lacquer based and that might be a problem? I don't understand paint enough to really understand what that means, why it's an issue, or how to tell if it is lacquer based.
IMG_4467.JPG
IMG_4466.JPG
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Maybe that makes it easier to understand what could be going wrong?
 

Rogviler

Well-Known Member
That is totally bizarre. The only negative thing that lacquer can usually do is lift the paint underneath, but you'll see that as bubbling or cracking. I've never seen it flat out melt everything... So when this melting off of the paint happens, does it then fully dry afterwards or does it stay tacky? You may just need to do very light mist coats. Like dusting the surface with quick bursts from 12+ inches away. I have experienced clear coat kind of softening metallic paint and sucking it up into the clear, and I can imagine if you sprayed the clear on until it was so heavy it ran it might do what you're experiencing. Hmm...

Well, one easy test would be to use all the same paints and clear but on a neutral surface like wood or metal. If it still does it then it must be the finish alone after all.
 

SuperSpark

New Member
That is totally bizarre. The only negative thing that lacquer can usually do is lift the paint underneath, but you'll see that as bubbling or cracking. I've never seen it flat out melt everything... So when this melting off of the paint happens, does it then fully dry afterwards or does it stay tacky? You may just need to do very light mist coats. Like dusting the surface with quick bursts from 12+ inches away. I have experienced clear coat kind of softening metallic paint and sucking it up into the clear, and I can imagine if you sprayed the clear on until it was so heavy it ran it might do what you're experiencing. Hmm...

Well, one easy test would be to use all the same paints and clear but on a neutral surface like wood or metal. If it still does it then it must be the finish alone after all.
It is so weird and it's not a one time thing either. I had to spray and repair the paint job of the first one several times because of this weird reaction and it's no coincidence because even with different paint and a different clear coat it STILL happened on the back of the second one. The weird thing is that when it dries, it's fine. It's solid and smooth and the paint does not all melt off so it still retains the colour. However it also solidifies and sticks to the bed on the opposite side, ruining whatever paint might have been on or around it. It doesn't just do it on a heavy coat of clear; the melting begins pretty much immediately. I REALLY want to finish these last 2 and perfectly finish the big one so I can put this project to bed (I hate painting TBH), but kinda scared to do so if I'm gonna just ruin it.

So far, I've found people give me different answers online, but no consensus on WTF is happening. Someone recommended I try finding an acrylic based clear coat since I'm using acrylic paint which I guess makes sense? I found an acrylic clear coat to potentially get, but what baffles me in my research for trying to understand paint and clear coat is how the hell what kind of clear coat things are unless it specifically says so and why this is occurring. On another site, someone told me that the Tamiya spray at least is a lacquer and so is the krylon potentially... But none of them say lacquer anywhere. Really want to figure it out before I buy yet another clear coat with potentially the same problem.

EDIT: Here's how the first finished one looks under the Tamiya Paints and Krylon Clear Coat. It's done and it's sealed mostly fine, but you can probably see a bit of evidence of me fighting against the clear coat. The darker area on the bottom right of the W is where the clear coat was melting when I poked it with the foam brush, in addition to the general melting elsewhere. I had to paint corrections over the clear coat and then clear it again... Twice. Not fun.

IMG_4471.JPG
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Rogviler

Well-Known Member
It's actually easy to tell what type of coating it is. If you look at the directions on the can and under "clean up" it says lacquer thinner then it's lacquer. If it says mineral spirits or acetone it's enamel. Plastic reactions aside, you generally want to use all of one or the other, or you can put enamel over lacquer but generally avoid lacquer over enamel since it can eat the enamel. I'll have to see if I can replicate the issue and figure out why.
 

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Aditrap

Active Member
RPF PREMIUM MEMBER
I’ve had this happen to me once on a print covered in XTC but I chalked it up to spraying the coats on too heavy/a combination of spraying a clear coat on a red lacquer layer. I saw some strange melting effect I hadn’t seen but ended up fixing it by repainting the red and using very thin clear coats a day after it had dried. I’m not sure if this is your same issue but I haven’t seen it since.
 

Lear60man

Master Member
RPF PREMIUM MEMBER
Here is my fool proof (nothing is foo proof haha) method of painting: Wash down prop with dawn dish soap in sink. Let dry. Pick up prop with clean cotton towel and wipe down with isopropal alcohol. I dont paint below 60 degrees and above 90 degrees. Oh and humidity should be below 60%. Lastly I make sure the clear coat and paint are of the same family (lacquer, oil, water etc). Read the directions on the back of product for dry times. I broke the humidity rule last week and watched a piece turn into orange peel right before my eyes. Humidity will fluctuate throughout the day and mornings are usually the lowest.
 

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