Cleaning resin parts

[Salamander]

Okay, I keep having problems with certain resin kits and primer adhesion.

So I wonder whether my preparation method is okay:

1) Remove parts from trees, remove tabs and other imperfections.
2) Wash parts under running tap water, give them a good scrub, sand off the more visible molding lines and tab left-overs.
3) Soak parts in water + dishwashing liquid for 1-3 weeks.
4) Scrub down under running water again, let fully dry.
5) Apply primer, let fully cure.
6) Wetsand remaining imperfections, if needed first apply Tamiya putty and let it dry for a few days before sanding.
7) Repeat steps 5) and 6) until happy.

Figure kits seem to be alright in general, but I keep having issues with mecha kits (all from the 1990s of earlier). Anything made from rougher resin works out fine (the figures often use this), but some older kits have this weird waxy finishing, and I have a hard time getting the parts clean enough. Often the primer (Mr. Hobby products) just flakes off. It's a pain in the behind.

So far I've tried two different dishwashing liquids, slightly better result with the stronger one. It can't be the water, right?

Any suggestions?

[Johnnycrash]

Other than NOT needing to soak the parts for weeks, looks fine.

Try a different primer. I use an auto primer for ALL my modeling. It's a little more aggressive, so test it out on scrap first. There are some primers known as "etching". These have an even MORE aggressive bit. Should be good for resin, as it is not known to melt under most solvents.

[Salamander]

Other than NOT needing to soak the parts for weeks, looks fine.

That's because whatever they used to prep the molds on the older kits is a total pain to remove. For most recent resin kits a few days seems to be enough. Makes me wonder if the problem might be that the mold release agent remains on the older kits are maybe completely dried out (all volatile parts gone) and whatever remains is just sticky like hell.

Try a different primer. I use an auto primer for ALL my modeling. It's a little more aggressive, so test it out on scrap first. There are some primers known as "etching". These have an even MORE aggressive bit. Should be good for resin, as it is not known to melt under most solvents.

I'll have a look at the DIY store later this week. Mr. Surfacer and Mr. Resin primer don't work on these kits.

[kenlilly106]

Have you tried cleaning the parts with a degreaser? Here in the States we have a product called "Super Clean" (used to be branded as Castrol Super Clean) that's a very strong water-based alkaline degreaser.

It will remove waxes, silicones, paint, chrome plating and its undercoat, etc. from kits. I don't know if its sold in the Netherlands but you might have something similar.

I will soak the parts overnight in straight Super Clean, scrub and rinse thoroughly and let dry. Make sure to wear rubber gloves, this cleaner is hard on the skin.

Another thought is to try cleaning the parts in lacquer thinner, this will remove about any surface contamination.

Something I've noticed about some kits is that even after cleaning with degreaser and lacquer thinner the surface can still feel very slick, I think in those cases its that the master and mold are very, very smooth and the resulting casting is super smooth as well. The solvents in regular primers can't etch into the resin so the paint stays on the surface.

In this case scrubbing the parts thoroughly with an old toothbrush and scouring powder such as Comet will lightly etch the surface and take the shine off the parts, this should give the primer enough 'tooth' to stay on.

Ken

[WildHouseModels]

Agree with the others here - you need to use a good degreasing agent but it also depends on the quality of the resin and how the casts have been created. The resin might have a coating on it from the mould release agent and this is what needs to be stripped off.

Using simple detergent in most instances work (or even using OXY Powder here in the UK if you are trying to get rid of a tough agent).

[Salamander]

Thanks all, will see what works best on this kit.

Of course, some more primer flaked off parts I superglued together, so it will also include discovering whether superglue can survive those products...

[Wug]

Don't soak. Most plastics will absorb a small amount of water.

Keep the trees, tabs and stuff you cut off the parts.

Clean the parts with Superclean or a tire cleaner. Wear gloves and maybe eye protection. Keep the cleaner away from pets and children.

If the parts don't feel clean, test lacquer thinner on the scrap. If it doesn't harm the resin clean the parts with lacquer thinner.

Mike

[seam-filler]

Using dishwashing liquid to do the initial clean is OK, but for soaking? - not so much.

Dishwashing liquid (particularly in Europe) has surfactants which means it lowers the surface tension. If you soak the parts, they will absorb some of this stuff - especially if the resin is a bit porous - which makes it hard for the paint to adhere to.

Degreaser is best. Actually, neat distilled vinegar is pretty good!

[starmanmm]

sometimes, if you do the above (minus the long soaking time) is to lightly sand the part will also help with primer attaching better.

[Lonewolf]

I usually only soak parts for an hour, maybe two at the most. Then I lay them out on paper towel and let then air-dry overnight before I start working with them.