Problem with Tamiya lacquer not curing properly...

[Carson Dyle]

I recently had an issue with a primed and painted surface not curing properly. I’m still not entirely sure where I (or it) went wrong, so I’m turning to the experts.

The kit in question is resin. After thoroughly washing and sanding the main body I primed it with Tamiya grey. Evercoat Easy Sand was used to spot putty a few small dings and dents. After getting the surface where I wanted it I topped the whole thing off with a final coat of Tamiya white primer. Allowing for the primed surface to cure for a few days, I sanded and buffed it out to a smooth finish. This process took a couple of weekends.

Next I proceeded with the topcoat, applying warmed Tamiya pure white lacquer via rattle-can (by this point the primed surface had been given a few days to cure). I laid down the paint in light mist coats, allowing 15 minutes or so between passes, slowly but surely building up a solid base coat. I spent about a half a day on this.

After achieving full coverage the painted body was set aside and allowed to dry. I’ve followed the process I’ve just outlined on dozens of models over the years, so none of this was new to me. Business as usual, working indoors in Southern California in (roughly) 70 degree temperatures (give or take 5 degrees) and low humidity.

After four days of drying time, I buffed out a few minor imperfections (dust particles) with 2400, 3200, 3600 grit and set the body aside for further assembly. So far so good; by all appearances the surface was now ready for final buffing/ polishing. But here’s where it gets weird…

A few days later, as I was inspecting the body for any stray dust bits I might have missed, I discovered that certain areas on the surface had become slightly “tacky.” Upon further inspection I discovered I was now leaving finger prints on certain parts of the model where the paint had become “soft.” Clearly some sort of chemical reaction was occurring (or not occurring) which was keeping the surface from properly curing.

Frankly, I’m at a loss. I’ve had a fair amount of experience getting glossy surfaces with Tamiya paints, and I’ve NEVER encountered a problem like this before – not even when I’ve built up more primer and more paint on the surface, and allowed less cure time before sanding. What really puzzles me is how I had been able to sand out the body after four days cure time with no sign of trouble, only to have the paint go wonky on me three days later. WTF?

I’m also no stranger to working with resin parts, but I can’t help but wonder if in this case the body “gassed out” some sort of chemical in a way that inhibited the paint from curing. It’s the only thing I can think of that might account for the sucky conditions I’ve described.

I don’t know if I can salvage the model at this point, and in any event I’m more interested in isolating what went wrong so I don’t repeat the error.

Sorry for the long description, but any help you may be able to provide is greatly appreciated.

[MPWR]

Originally Posted by Carson Dyle

I can’t help but wonder if in this case the body “gassed out” some sort of chemical in a way that inhibited the paint from curing.

That's exactly what it sounds like, especially in that the problem appeared days after spraying. In which case it is not so much a 'mistake' you made as a simple incompatibility between the resin used and Tamiya (and likely all) lacquer paint. I very much doubt that there is any primer or other technique that would have allowed you to spray lacquer on this model without it reacting later.

There are alll kindsa resins out there, with alll kindsa strange ingredients in them. Many (most?) are perfectly stable and paintable. But some are decidedly obstinate, And will never be paintable with some paints. I found a brand of resin years ago sold for modeling that softens styrene. A decade after completing the build, the solvents in the resin still keep styrene in contact with it soft and molten. I don't use that stuff anymore....

Who made the kit?

[CrateCruncher]

I also would suspect the resin is the culprit here. A while back I mixed some "iffy" looking resin that was about 3 years old. One of the bottles had solid flakes floating in it. I mixed up a batch and it cured but left an oily residue on the surface. Who's resin is it?

[Carson Dyle]

Thanks for the replies.

I've heard war stories over the years involving resin-related mishaps (e.g. incompatibility with lacquer) but I've never fallen prey to this sort of snafu until now. Bound to happen sooner or later, I guess.

The unfortunate thing is this kit was produced by a buddy of mine who's been working on it for years. I was doing the first build-up for him to use as a marketing sample.

If there's one thing worse than screwing up your own model it's screwing up someone else's. Thing is, at this point, I'm not sure what I could have done differently.

[CrateCruncher]

Dude,
You didn't screw anything up. If anything, he wasted your build time by giving you wonky resin. I'm sure he'll appreciate you telling him about the problem.

[Didymus]

Sounds like you followed the right procedure for resin. Some people soak resin bodies in Bleche Whyte or other bleach solutions; I soak mine in regular household bleach, and then scrub them with Soft Scrub with Bleach. But I'd still go with the majority and say the problem was with the resin and not with the modeler.

In my experience, Tamiya primer is the most stable and least reactive primer you can buy. It sticks to practically anything and doesn't react chemically to metal, plastic or resin surfaces. So something was very wrong with that resin, IMO.

You will be doing your friend a favor if you tell him what happened.

[freakmech]

When working with resin I like Gunze Mr. Resin Surfacer alot. Ive had "soft" spots before using Tamiya products but laying down Mr. Surfacer first has eliminated this so far. I can then spray Tamiya fine primer over the Mr. Surfacer. Im not sure if the resin is the culprit or the mold release used but either way your friend might want to experiment with the products used before thinking about releasing this kit to the public, if at all is the intention.

[klutz_100]

1. The good thing is that all your friend has to do is try another resin. I personally use Axson resins and have no incompatibility issues with Tamiya, Gunze or Zero paints over both Gunze resin primer and Tamiya primer.

2. It might be worth your while stripping this model back to the bare resin and trying again with a different primer. I think that either Zero Resin Primer or Gunze might be worth a try. You might find that they create a better barrier. At least you will be richer for the experiment

3. It might be useful for all of us if you could let us know what resin he actually used. It might help others avoid similar issues in the fututre?

[Carson Dyle]

Originally Posted by Didymus

I soak mine in regular household bleach, and then scrub them with Soft Scrub with Bleach.

That’s essentially my technique a well. As I said, I’ve never encountered a problem like this before, but in any case bleach did little to help.

Originally Posted by freakmech

When working with resin I like Gunze Mr. Resin Surfacer alot.

I’m picking some up this AM and will give it a try. I also have a batch of self-etching primer recommended by my local auto supply finisher, so I’ll runs a couple tests with that as well.

Originally Posted by klutz_100

It might be worth your while stripping this model back to the bare resin and trying again with a different primer.

Yeah, I’ve already begun stripping. What a mess – but, as you say, it’s been, and continues to be, an educational experience.

Originally Posted by klutz_100

It might be useful for all of us if you could let us know what resin he actually used. It might help others avoid similar issues in the fututre?

I’ll see what I can find out.

The fellow who cast the parts has apparently used the same brand of resin for many years without ill effect. Who knows; maybe I just got a bad batch.

Anyway, thanks a million for the thoughtful replies. They are greatly appreciated.

[MidMazar]

I agree with everyone else. Has to be the resin. Like a few stated before me, strip it and try a less harsh primer like gunze.

Also what could have happened was the body wasn't cleaned thourghly enough before applying primer. As you say it only happened in a couple spots. But that might be the case, im leaning with everyone else. Bad resin.

[MPWR]

Originally Posted by klutz_100

2. It might be worth your while stripping this model back to the bare resin and trying again with a different primer. I think that either Zero Resin Primer or Gunze might be worth a try. You might find that they create a better barrier. At least you will be richer for the experiment

Not to be critical, but that actually seems rather pointless. Why waste the primer, paint, and time on a surface that you don't expect will be paintable? If the resin is outgassing solvents (which we have reason to believe it is), no amount of 'the right' primer is going to seal it or act as a barrier for paint above it. This is not a matter of picking the right products. In all likelihood, this part will continue to outgas for many years to come- and it will continue to ruin whatever is painted onto it.

[klutz_100]

Originally Posted by MPWR

Not to be critical, but that actually seems rather pointless. Why waste the primer, paint, and time on a surface that you don't expect will be paintable? If the resin is outgassing solvents (which we have reason to believe it is), no amount of 'the right' primer is going to seal it or act as a barrier for paint above it. This is not a matter of picking the right products. In all likelihood, this part will continue to outgas for many years to come- and it will continue to ruin whatever is painted onto it.

Criticize away, Andy I was only thinking out loud

I really don't know the definition of outgassing and I am anything but a chemist (I did google it though and the definitions I found kind of matched my intuition) but I would have thought this had been caused more by a chemical reaction with the resin rather than "the release of adsorbed or occluded gases" :O That's why I was thinking that a different barrier coat may produce different results..? Who knows? You may very well be right but I would still be inclined to try it anyway just because I am bloody-minded

[Carson Dyle]

I decided to strip the paint just for the hell of it. I re-primed the effected parts with self-etching primer, and am now going to wait a couple weeks to see what happens. Call it idyll curiosity.

Meanwhile, because I have serious doubts that the stripped parts will ever be usable, I've requested a set of replacement parts from the manufacturer -- parts not derived from the same batch of tainted resin. I'll prime and set these aside for a couple weeks as well. With any luck the replacements will hold their gas, as it were, and I'll be able to chalk the whole thing up to experience.

Thanks again for taking the time to help a brutha modeler out.

[Didymus]

Originally Posted by klutz_100

You may very well be right but I would still be inclined to try it anyway just because I am bloody-minded

Ditto. It would be a shame to toss the casting after only one try. I would bet MPWR a bottle of Gunze Mr. Resin Surfacer ($6.00) that using it after vigorous scrubbing with cleanser-with-bleach will solve the problem. And something might be learned in the process. (Knowledge is priceless, right?)

Carson, have you told the resin caster about the problem?

[Carson Dyle]

Originally Posted by Didymus

Carson, have you told the resin caster about the problem?

Oh, yeah.

The guys responsible for the kit in question have been nothing but helpful in terms of isolating and correcting the problem.

As I mentioned above, this is a first ever "demo" build of this particular model -- a model that has yet to be made available to the public (for obvious reasons, lol). Having worked very long and hard to get this far the last thing the manufacturers want is to send out faulty parts.