FoW primer and Model Master vs krylon

[fitterpete]

No I don't want to know which is better
But why they weren't compatible on my tanks? And why only some of the tanks?
OK heres the story.
I primed about 20 vehicles or so with Krylon flat black.About half Warlord half JTFM and Company B.I did not wash them beforehand.The krylon primer took to all the tanks anyway so washing is a non issue.They have been primed for about a week so primer is dry.
So today I spray a couple with FoW British Armour paint and a couple with a Model Master Olive Drab.Heres where it gets weird.
SOME parts on SOME models get bubbly looking and both new spray and old primer can be wiped off with a casual touch.Its like the new paint melted the primer but other parts on the same models have dried fine.
I once had a set of schurzen from Percision Models Design that did the same thing but it was the whole thing not just parts of it and the primer never took either.I washed them with about 3 different things and those parts never did take any kind of paint.PMD replaced them for me though.

Anyone have any ideas? I'd like to avoid this in the future but I'm not sure what went wrong.
I've also used this method on about 40 Tamiya and Bandai kits and never had a issue.

[grant]

First off, you need to wash your tanks. Resin sucks unless it is clean. After you wash, everything's better.

[fitterpete]

The primer was fine and the tanks weren't washed.I painted and sold over 700 FoW resin vehicles and never washed a one.Guess I was lucky.I will say I havn't much experience with the 28mm companies resin(as most of my stuff is 1/50 corgi or 1/48 Tamiya kits) I've only done about 10 vehicles from PMD.I figured the washing thing was BS like it was with the FoW models.

I did think of something else though.I touched up the prime job with Tamiya acrylic brush on.From the way that stuff smells I think they have a alcohol base.
Isn't there some rule about you can't paint enamel over acrylic?

[Evan]

There is a generalisation that you shouldn't mix types of paint but it has more to do with out in the real world like real aeroplanes, boats and cars etc. You can safely put most modelling paints over the top of each other - acrylic over enamel and visa versa. For a good primer over everything, including resin, try Humbrol matt black enamel thinned down 30-50%, you won't get any grease or dirt issues. The usual problem with differing paints is where one has particularly aggressive solvents that will eat anything not compatible under it, lacquers usually fall into this category.

[Comte Michel]

Primers tend to be relatively porous to provide a 'tooth' for the layer of paint to hold on to when applied over the top of it. As such, anything underneath can percolate through and affect your finish. You might not be able to see a layer of mould release or unreacted resin, but you nevertheless can't be sure it isn't there.

So, long story short, like grant says, ALWAYS wash resin or plastic models. Even moulds for metal are often treated with talc, so best wash those too in my opinion if you want to be sure of the results.

If you touched up the primer with Tamiya paint, then you will have created patches of less porous surface, which rather explains exactly what happened. Just fyi, Tamiya paints use a isopropyl alcohol base, whereas most other acrylics are water based. I've found it's best not to mix Tamiya with anything else, but painting over the top of Tamiya with other paints isn't a problem.

There is no problem with painting enamel over acrylic and vice versa. The problem lies with painting cellulose over enamel. So if you use a car primer, you can't re-prime an already painted model because bad things happen.

[fitterpete]

Hey everyone thanks for the answers.Well I guess I will
1) Wash my resin vehicles(What a PITA but its not like I'm doing hundreds of them like the 15mm stuff)
2)Not use Tamiya paint to touch up the prime job(I was out of my regular brush on black so no probs there)
I only have about 6 Tamiya colors and they are all dark base coats so I guess I always painted over them with brush on acrylics not sprays.
Come to think of it I never used any sprays on all the FoW vehicles either.Everything was hand painted except for the black primer.
I still have about 15 28mm German vehicles that are all ready primed black and it seems to be stuck on pretty good.As I don't use any sprays on German stuff(havn't found a base coat that is dark enough to start dunkelgelb for my taste yet)I think I'll go ahead and try to finish one up.
Thanks Pete

[grendels father]

I've gone through this with the resin that JTFM and CoB use. Krylon is ok but testors LACQUER primer works best! especially if you give the resin a quick wash with lacquer thinner. Have not had this problem with Warlord/Bolt Action resin...

[Vogless]

I've had occasional, extreme, problems with that resin.

I've use enamel, adhehesion promoter, washing in everything up to Gasoline.....

My last model with that resin worked out OK, but I can't get paint to stick as well as the Warlord resin.

Now, I have a friend who reports no trouble at all. I have no idea....

[fitterpete]

My problems were with Warlord,JTFM, and Company B vehicles(AEC armored car,Staghound,Chaffee respectivly).So it wasn't a problem with any one resin.

[Vogless]

REALLY? Huh.

I'm surprised. Never had any issues with BA. I just wash with dishsoap, prime with auto primer.

Let us know what works best for future reference.