Gray detail/now tan detail cleaning/surface prep?

**BraselC5048** · 08-08-2023 14:48

My first attempt at test-painting a gray detail (which apparently now is tan detail) model resulted in thinned Vellejo matt black (always dries perfectly flat and smooth in an hour or so) still glossy a day later, and apparently a tip of a fingernail can scrape it off. To me this suggests poor surface adhesion. I'm assuming I messed up the gray detail surface prep. (I suppose that the tan detail that replaced it is identical, except tan?)
My surface prep consisted of a one hour soak in full-strength Simple Green, then rising under the faucet, then a couple hours soak in clean tap water, then being mostly dried with a largely lint-free towel before being left to finish air-drying. I had 'thought' this was about correct. I'm assuming I messed something up, so what's the correct gray detail pre-painting cleaning and surface prep process?
Thanks.

**ReducedAirFact** · 08-08-2023 15:21

I think the material is so new that we're all learning together, but I have to think that a spray primer coat would help with adhesion.

**malachi** · 08-08-2023 15:24

Seems like the Simple Green prep should be fine, although I don't usually do that (it's a good idea to remove any solvents, etc though). Perhaps it wasn't completely dry?

I normally spray a couple coats of Rust-oleum Matte Clear to seal/fill "pores" then prime it in black or khaki. Sometimes I'll seal it with another coat or two of Matte Clear after the base coat is on if I'll be handing it a lot during painting (ones that are mostly PC10 or silver).

**BraselC5048** · 08-08-2023 16:30

After I took it out of the water soak it sat out for something like two weeks. I used to use Model Master flat black spray enamel, (spray can), which is normally pretty forgiving and firmly adhering to just about everything, but on Shapeways stuff I'm hesitant to use anything other then acrylic, since FD reacted with anything else. We're sure that what's now tan detail is safe to use enamel on? Vallejo paints aren't particularly good in the adherence department, and the symptoms fit a slightly slippery plastic.

**ReducedAirFact** · 08-09-2023 01:02

I used a spray primer on my test print. ( Primers are *meant* to stick.) But I don't remember the brand. You are wise in saying you should always test a primer or paint on some obscure part in case there is a reaction.

**Jager** · 08-09-2023 10:05

Originally Posted by BraselC5048

Vallejo paints aren't particularly good in the adherence department, and the symptoms fit a slightly slippery plastic.

That's interesting. I use Vallejo almost exclusively, and haven't had an adherence problem. I usually use a different brand primer, but I have used the Vallejo primer in the winter (no spraying).

Karl

**CrashCraig** · 08-09-2023 12:00

Another data point-I've used the Model Master Primer brand on Shapeways including Grey PA12 as well as all sorts of miniatures for many years and never had a problem with it adhering to the model as well as holding acrylic or enamel paints.

**Flying Helmut** · 08-09-2023 13:36

I have never primed any Shapeways planes.
I have never needed to.

**Larry R.** · 08-09-2023 14:54

I don't know if it is necessary to clean 3D printed models. Resin or injection moulded kits need cleaning due to the mould release agent.

**BraselC5048** · 08-09-2023 20:11

Originally Posted by CrashCraig

Another data point-I've used the Model Master Primer brand on Shapeways including Grey PA12 as well as all sorts of miniatures for many years and never had a problem with it adhering to the model as well as holding acrylic or enamel paints.

Originally Posted by Jager

That's interesting. I use Vallejo almost exclusively, and haven't had an adherence problem. I usually use a different brand primer, but I have used the Vallejo primer in the winter (no spraying).

Karl

I always did (pre-Shapeways) a basecoat (no primer) of Model Master flat black, then touched up the inevitable spaces that were missed with thinned Vellejo flat black, then painted on top of that. The Model Master spray cans stick to just about anything, but the Vallejo which I do use exclusively I've noticed that, if the spray flat black is rubbed off, sticks fine to resin and injected model (probably stryene) plastic, but against white metal it rubs off easily.
After discovering FD from Shapeways reacts with enamel on those I used thinned Vallejo flat black on its own, and it worked perfectly.

But this "failure to dry" problem has only occurred before on the clear plastic Shapeways discontinued a while back. I'd imagine it would occur on the actel plastic commonly used in model railroading due to its slippery nature (low friction for wheels and trucks) and flexibility (it springs back easily, used for protruding parts, and to make parts that attach by flexing it to get it to fit into holes, after which it goes back into the correct shape.
I've got no doubt a spray enamel flat black would stick to it, I'm just worried about discovering six months from now after they're all painted that the now tan detail plastic reacts with it. It doesn't seem likely, and if it wasn't Shapeways it could be taken for granted, but I don't know if being fine with enamel is something I can safely assume.

**ReducedAirFact** · 08-09-2023 23:24

Originally Posted by Larry R.

I don't know if it is necessary to clean 3D printed models. Resin or injection moulded kits need cleaning due to the mould release agent.

It probably depends on the material. Versatile Plastic (nee WSF) and PA12 materials are supported by unfused powder, so there's nothing to " wash off" except loose powder. The now-discontinued FUD was supported by a layer of wax which was melted off in a hot oil bath. The oil was supposed to get washed off, but sometimes some was left behind. I'm not sure what supports this new material during printing.