Resin + acrylic + lacquer clear coat = tricorder problems. :S

norbauer

Well-Known Member
RPF PREMIUM MEMBER
I have been having a less than entirely fun experience painting a resin-cast Mark VII tricorder.

I primed with self-etch, painted with Krylon gloss acrylic, sanded, dusted with Krylon silver, and then applied a lacquer clear coat (Watco Clear Satin). Unfortunately, anything other than the lightest of mistings of the clear coat causes the topcoat to wrinkle and crack down to the primer. Very light mist is fine, but anything enough to wet the surface markedly tends to cause this monstrosity:

WP_20140908_004.jpg

Which means I have to sand back down to around the border of the primer and gray and start over.

Some experimentation has led me to the conclusion that this is an issue of a chemical incompatibility between the acrylic and lacquer. Namely, the lacquer seems to be acting as a solvent to the acrylic, even though it is entirely dry. I have another prop that I painted using laquer-based paint and I tried applying the same laquer clear coat on top of that copiously (far more than the tricorder ever got) and there was no sign of cracking at all. So, as I say, it seems to be an issue of incompatibility between the chemicals. Why the problem doesn't occur with just a light misting is entirely a mystery to me, but using many very very light coats actually does work, notwithstanding the anxiety of trying to apply it without overdoing it.

WP_20140908_005.jpg

Here is my puzzle: now that I've managed to get the prop to accept a clear coat using the lacquer with multiple light coats is also when I have worked out the cause of the problem, so my question is: should I sand everything back down and start over, or leave it as it is (looking fine now) and just cross my fingers that something isn't going to do wrong down the road? My fear is that somehow the lacquer coat is going to dissolve the paint over time and end up cracking anyway.

Any other ideas as to what's going on here chemically or in terms of my technique would be most appreciated. My surmises above may be entirely incorrect.
 
There's a difference between "dry" and "cured" when it comes to paint. "Dry" simply means that the paint won't transfer if you touch it. "Cured" involves the paint bonding to a surface and hardening (as well as being "dry"). Some resins make this harder, though you did use some self-etch primer for extra stick. And lacquer on top of acrylic can cause problems if the acrylic isn't totally cured. (Though I've had instances where I've aggresively applied lacquer (or enamel) over acrylic with no ill side effects.) And perhaps the acrylic ddin't fully bond to the primer, so it is softening from both the lacquer and the primer......

How long between applying the primer did you apply the acrylic color coat? And how long after the color coat was down did you apply the lacquer?

Something you may want to consider is applying several coats of your color coat (to build up thickness) and then do a combination of wet sanding with high grit sandpaper (start @ 1500 and go up to about 8000) and polishes. This will get you a high gloss finish without the need for a heavy clear coat. If you still want to seal the paint after polishing, use light coats of clear lacquer and wet sand that.......

Gene
 
There's a difference between "dry" and "cured" when it comes to paint. "Dry" simply means that the paint won't transfer if you touch it. "Cured" involves the paint bonding to a surface and hardening (as well as being "dry"). Some resins make this harder, though you did use some self-etch primer for extra stick. And lacquer on top of acrylic can cause problems if the acrylic isn't totally cured. (Though I've had instances where I've aggresively applied lacquer (or enamel) over acrylic with no ill side effects.) And perhaps the acrylic ddin't fully bond to the primer, so it is softening from both the lacquer and the primer......

How long between applying the primer did you apply the acrylic color coat? And how long after the color coat was down did you apply the lacquer?

Something you may want to consider is applying several coats of your color coat (to build up thickness) and then do a combination of wet sanding with high grit sandpaper (start @ 1500 and go up to about 8000) and polishes. This will get you a high gloss finish without the need for a heavy clear coat. If you still want to seal the paint after polishing, use light coats of clear lacquer and wet sand that.......

Gene

Hi Gene. Thank you for the thoughtful response. I am vaguely familiar with the distinction between drying and curing, though I don't really have a good feel for the curing times of different paints. Is there any way to gauge this?

I waited over 24 hours between the last pigment coat and the first light clear coat. I did a few more light clear coats that same day and then waited another 24 hours and applied a second set of clear coats. One of those was accidentally heavier than I intended, which is what resulted in the cracked image above, which destroyed the finish by cracking all the way down to the primer (not easy to see in the image).

The reason I wanted the clear coat is actually to have a smooth but unpolished finish. I can only find my pigment color in gloss, but wet sanding that and clear coating on top gives a nice matte finish (when it doesn't destroy everything). Otherwise, the polishing technique you describing would work very well.
 
I always use Acrylic lacquer when I use Acrylic paints, never car lacquer or this happens:(

I'm actually using a high-end lacquer used for woodworking and musical instruments, but I think the same tenet applies.

It was no big deal really though. I just sand back down to the primer (or thereabouts), repaint, re-dust with silver, and then clear coat again. Laborious but fortunately the cast itself wasn't damaged.
 
Oh man, sorry about the crinkled paint. I've been there before and it's painful.

Which Krylon were you using, specifically? I think most of their current offerings are enamel (including the "Colormaster" line in which you would find your Stone Grey/Castle Rock that are the current TNG Dove Grey equivalents). And lacquer over enamel will lift the paint (unless as you noticed you go very very light with the lacquer coats).

As far as satin coats you can go with the light coats of the lacquer, though you risk ruining the paint again with the slightest over-application (though it might be better to allow several days, not just one, before applying any clear over gloss Krylon... that stuff seems to take forever to cure).

I have had nothing but trouble with the current Krylon clear offerings, both satin and matte. It doesn't work as well as it once did. Recently I have been using Testors Dullcote and Glosscote, which is a lacquer but is formulated to be compatible with enamels (as that is a large part of that company's product line). It is unfortunately rather expensive but I at least know it works. Even if I have to do a kind of mix of the two to get a satin rather than matte or gloss effect. It is available in a bottle to be airbrushed as well.

Hopefully someone else has a better clear coat suggestion for you... I could use the advice as well! :)
 
Oh man, sorry about the crinkled paint. I've been there before and it's painful.

Which Krylon were you using, specifically? I think most of their current offerings are enamel (including the "Colormaster" line in which you would find your Stone Grey/Castle Rock that are the current TNG Dove Grey equivalents). And lacquer over enamel will lift the paint (unless as you noticed you go very very light with the lacquer coats).

Yeah, the frustration for me has mostly been in not knowing what was causing the issue, so this thread is helping me feel a bit better. At least now I have a strategy for avoiding the problem in future.

As for the Stone Gray, I am using this one. It doesn't appear to have a line name per se and it doesn't call out its chemical composition, but I have been assuming it's acrylic enamel.

As far as satin coats you can go with the light coats of the lacquer, though you risk ruining the paint again with the slightest over-application (though it might be better to allow several days, not just one, before applying any clear over gloss Krylon... that stuff seems to take forever to cure).

I have had nothing but trouble with the current Krylon clear offerings, both satin and matte. It doesn't work as well as it once did. Recently I have been using Testors Dullcote and Glosscote, which is a lacquer but is formulated to be compatible with enamels (as that is a large part of that company's product line). It is unfortunately rather expensive but I at least know it works. Even if I have to do a kind of mix of the two to get a satin rather than matte or gloss effect. It is available in a bottle to be airbrushed as well.

Hopefully someone else has a better clear coat suggestion for you... I could use the advice as well! :)

The Testors recommendation is excellent; thanks! I just ordered a couple of cans to try to compare it with the Krylon Satin Clear coat (which I also ordered). I like that the Testors also comes in a bottle for airbrushing, which is the next skill I hope to pick up.
 
All good advise here.
I try to use all one kind of paint for compatibility.
If you're going with a lacquer based primer, let cure for a few hours before going with your first color coat which should also be lacquer.
Give it a day or two to air out and hit it with Polyurethane for a smooth finish.
 
You are right on with your guess of solvent incompatibility. Lacquer paints are much more robust and their solvents can attack weaker paints like enamels or acrylics. You can paint any other paint over lacquer, but you have to be cautious painting lacquer over acrylics and enamels. Light coats (like you did) are the best way. That gives the solvents in the lacquer a chance to evaporate quicker so they don't have as much of a chance to affect the underlying paint. Once the lacquer's solvents have evaporated, your underlying paints should be fine.

Another factor is the way paints dry - particularly gloss paints. Gloss paints are designed to skin over, which is what creates the glossy surface. The paint also contracts slightly as it drys, pulling the skin tight. A by-product of that process is that the skin traps solvents in the wet paint under it that then take longer to evaporate. So a gloss coat can feel dry on the surface, but still be soft underneath. When another paint; like lacquer, is sprayed over this hard/soft sandwich, it contracts too. It pulls on the skin of the paint which tears it away from its soft under layer creating the crackling texture we all cringe at. (unless you are painting a 10th doctors sonic screwdriver, ha ha!)

So the best advice is to use all the same type of paint, or at least spray enamels over lacquers and not the other way around.
 
Krylon reformulated their paint recently. The "regular" consumer grade is garbage. what you want is their Industrial grade, that's the original formulation. In fact,several paint companies have reformulated their paints such that the paint takes much longer to cure. Cure times have gone from several hours to several days! Rattle can paint is quick and easy but with new EPA regulations (especially in California) is ,at least in my opinion, making rattle can spray paint a less attractive option. Invest in an airbrush and mix your own paint as one more tool in your arsenal.
 
I primed with self-etch, painted with Krylon gloss acrylic, sanded, dusted with Krylon silver, and then applied a lacquer clear coat (Watco Clear Satin).

That is your problem right there. I have worked in the paint industry, for a manufacturer, for the last 15 years (specifically in the wood coatings area). The Watco product you topcoated with is a solvent-based nitrocellulose (NC) lacquer. You applied that over an acrylic paint. The solvents in the NC lacquer (toluene etc) are not compatible with acrylic paints. They are too "active" and will cause acrylics to crack or wrinkle. You might get away with light mist coats but that is still not a good idea. It does not matter if the acrylic is dry or even fully cured. These two coatings are not compatible.

Bottom line, if you're using acrylic primers and basecoats then use an acrylic lacquer to topcoat. If you're using enamels then topcoat with enamels. If you want to use the lacquer then you need lacquer based primers & topcoats but good luck with that as they are rarely available to consumers.

Also, NC lacquers do not make good topcoats. Yes they are quite durable and easy to apply, the NC resin is VERY VERY susceptible to yellowing from UV light exposure. They also tend to not age well. Case in point, look at old 50 year old guitars and see how the finished checks and cracks over time. That's what you can expected from NC clearcoats years down the road.
 
Great info here, everyone; thank you!

That is your problem right there. I have worked in the paint industry, for a manufacturer, for the last 15 years (specifically in the wood coatings area). The Watco product you topcoated with is a solvent-based nitrocellulose (NC) lacquer. You applied that over an acrylic paint. The solvents in the NC lacquer (toluene etc) are not compatible with acrylic paints. They are too "active" and will cause acrylics to crack or wrinkle. You might get away with light mist coats but that is still not a good idea. It does not matter if the acrylic is dry or even fully cured. These two coatings are not compatible.

Bottom line, if you're using acrylic primers and basecoats then use an acrylic lacquer to topcoat. If you're using enamels then topcoat with enamels. If you want to use the lacquer then you need lacquer based primers & topcoats but good luck with that as they are rarely available to consumers.

Also, NC lacquers do not make good topcoats. Yes they are quite durable and easy to apply, the NC resin is VERY VERY susceptible to yellowing from UV light exposure. They also tend to not age well. Case in point, look at old 50 year old guitars and see how the finished checks and cracks over time. That's what you can expected from NC clearcoats years down the road.

Given the above, would you recommend I sand back down to the primer, redo the paint job, and then use something like Testor's dullcote for the clear coat? This would be my third time doing that, so I'm kind of getting used to it. ;)
 
Testors Dullcote, I'm not overly familiar with that product. Testors website says it can be used over enamels and acrylics. What I would recommend if you are already using Krylon primer and Krylon silver then you should go get some Krylon Acrylic Clear Lacquer. They have it at Home Depot for sure. That way you're safe because you are using all acrylic and all from the same manufacturer. That's the safest route.

I really like the Krylon Acrylic Clear Lacquer. Its great from models. I actually use it over waterslide decals on headstocks for guitars. No I don't work for Krylon but given what you are already using, this makes sense.

One other note to avoid confusion; there is a BIG difference between the acrylic lacquer like I am suggesting for you and the solvent-based NC lacquer that you used. The only thing they have in common is the name lacquer. Technically an acrylic lacquer isn't even a lacquer at all.

Hope this helps.
 
Thanks everyone for the excellent advice in this thread. I wanted to share a few useful resources I've found

Firstly, here is a YouTube video by a professional model-maker. At 5:12, he talks about exactly the problem described above.
http://www.youtube.com/watch?v=qRFjBp5TTwc

Secondly, here is a great resource on paint problems and solutions in modeling (with photos):
http://modeltech.tripod.com/paintprobs.htm

As to my tricorder, I sanded back down to the resin, re-primed, re-painted, re-dusted with silver, and clear-coated again, this time using Krylon as suggested above. I let the clear coat sit for about four days and then, further manifesting my extreme paint neophyte foolishness, I took it home and gently set it on a cloth and then took off for a week-long trip to San Francisco (to see George and Gracie, of course). When I returned, the weave of the paint cloth had left an imprint in the clear coat! :S Now I'm hoping to sand back down through the clear coat without hitting the base and dusting coats to then clear coat again. Apparently, the curing time for the clear coat is very long. It seems I can't win, but I suppose there is something to be said for learning by making all the mistakes first-hand.
 
This thread is more than 9 years old.

Your message may be considered spam for the following reasons:

  1. This thread hasn't been active in some time. A new post in this thread might not contribute constructively to this discussion after so long.
If you wish to reply despite these issues, check the box below before replying.
Be aware that malicious compliance may result in more severe penalties.
Back
Top