Primer adhesion problem

I'm back in action, after a full day of work just on the six piece sleeper.

I wanted to be sure, so I soaked the entire sleeper in oven cleaner for a few hours and all remnants of primer washed right off.

I then used lacquer thinner to release the glue and take the entire sleeper apart. I did this because I was sure that the pieces could be fit a little better and I was correct. Reassembled it all, refilled some gaps and then applied Rustoleum Painter's Touch plastic compatible primer.

The cab and hood did not have any filler or grooves and the primer literally peeled right off with masking tape. They came out perfectly clean and I applied the primer to them as well today.

Tomorrow I will wet sand and fill a few tiny spots and everything should be good for the top coat.

The primer can says the best adhesion to plastic takes 5-7 days so I won't be doing top coat until the weekend again, but after what I went through I'd wait a month if that's what it said. LOL

Thanks for the tips, advice and observations everyone, it is greatly appreciated and I hope that I can be of help here in return in the very near future.

There you have it. Model Master Acrylics have some serious adhesion problems. Prime with some primers that have more "tooth" such as Mr Surfacer, Tamiya White Surface Primer, Humbrol, etc... anything but Model Master Acrylics.

I would always use enamel primer. Always.  The only genre I would even think about spraying acrylic directly on clean styrene is armor. 

For a truck build like yours use enamel first.

I'm building the Italeri Magirus Deutch truck right now.  It was primed with black MM enamel first, then the finish coats of Tamiya Acrylic maybe 4 days later.

I've never had a problem in decades, with lots of masking.   I also use Tamiya yellow masking tape. It just works better.

I'm not at all an expert regarding primers, but here's what I have experienced. I think many of the model paint primers are not primers at all, just flat paints. To have good adhesion you need a primer that will have good properties for "sticking"on the surface, and allow for sanding and masking.

I have had the best luck with Tamiya spray can, and Badger Stynylrez primer applied with an airbrush. As long as the surface is well cleaned prior to priming, I have experienced no lifting when sanding or masking at later painting stages, using these primers.

I don't know much about the commercial primers in spray cans, but there are some good ones out there, that others on FSM have used with good results. I suspect they may be a bit hotter and give good adhesion, like in a lacquer form that "bites" the plastic a bit. But care must be used there, if it's too hot it may melt and deform the models surface.

Hope you get the model squared away.

Patrick

I've never had any luck with the MM Acrylic Grey Primer. I have had the exact same problem you are describing. My experience happened on a build of the Revell/Monogram 1/72 F-22. I had washed the sprues in warm (not hot) dishwater and then let dry, after the kit was assembled, I wiped down the plastic with 91% ISO and the stuff could almost literally be wiped off with my fingers in some spots, and other spots were fine.

If you are set on using an acrylic primer, I would recommend Stynylrez from Badger, so far, I've not experienced paint lifting from the surface during masking or handling. I also recommend the Tamiya fine surface primer and have used other rattlecan primers like Krylon, Rustoleum and Plasticote. Recently, I've noticed that the Krylon brand has changed something and it does not work as well as it used to.

stikpusher

Acrylic or Enamel?

 

Acrylic or Enamel?

BlackSheepTwoOneFour

What primer were you using?

 

What primer were you using?

Hello!

I say if the steel wool did it and didn't need all day for it, then the primer just didn't stick, good thing it's off now. You say the filled and sanded panels had a better adhesion - that would point to some problem with the surface. Maybe it would be a good idea to wash it more aggressively - like with some solvent that wouldn't attack the surface. You could try to wipe it down with Gunze Mr colour thinner or Model Master enamel thinner - or their equivalent from the hardware store, to save some money. Just be careful to test it before on scrap, so as not to damage the model any further. And it would probably still be a good idea to switch to another primer, one that isn't so sensitive as to the surface it's going on. Once again - good luck and have a nice day

Paweł

Thank you. I did manage to get most of it off with steel wool under running water.

The panels that had seen filling and sanding have the primer stuck really well. I'm hopeful I can salvage this without leaving any marks in the top coat when it's applied.

Hello!

That's a really bad feeling, sorry to hear that! Sounds like you did most of the things right - surface washed, scuffed - should be OK. There are many factors that could have gotten in the way, still - things like humidity, or maybe the primer went wrong on you - started polimerizing in the bottle or dried mid-air, before reaching the surface - hard to say. The thing to deteremine now would be if the lack of adhesion is local or more like global. If it's local, you can try to sand single panels or surfaces that are affected and only re-do those. But it probably is easier and faster to remove the old paint (brake fluid, oven cleaner, drain cleaner) and start all over again. I like automotive spray can primers as my first coat, because they eat into plastic some and stick really good. You just have to watch that you get a brand that is not TOO agressive. Tamiya spray can primer is a really good stuff, too. So - good luck with your project, I hope you can save it - have a nice day

Paweł