When to apply etch primer on a multi-material kit?

[Mol_PMB]

I'm building a 7mm loco kit which is mostly nickel silver, some brass, but with many 3D-printed components (chimney, dome, smokebox door, water fillers, brake gear, sandboxes etc)

The last multi-material loco kit I built I used Halfords grey primer, which went on very well but has been susceptible to chipping off again on the nickel silver parts.

So this time I'd like to try an etch primer.

 

My question is, should I apply the etch primer before I attach the 3D-printed components (i.e. when the loco is 100% metal) or should I glue the 3D-printed components on first and then etch-prime?

 

Here's a pic of the loco with some of the 3D-printed components just placed in position. Note that it can be separated into sub-assemblies for painting (footplate, tanks, cab and bunker, roof, smokebox, boiler, chassis).

 

I'd also be interested in recommendations for which etch primer to use.

The final condition of the loco will be mostly black and weathered, like this:

(thanks to br2975 for the image, linked from where he posted it on the MSC Railway thread)

 

Many thanks

Mol

 

 

 

 

[Enterprisingwestern]

I'm a U-Pol etch primer man, and in my experience (so far anyway) plastic and resin isn't affected by it, so I use it as normal at the end of the build.

Although it is an etch primer, it's not like you're spraying neat sulphuric acid on the model.

 

Mike.

[michl080]

Hi,

 

I agree with Mike and would like to add that you generally can't glue anything on a painted surface. Fix the 3d-parts on the metal and prime it afterwards. I am doing it that way all the time.

 

Michael

[Mol_PMB]

Many thanks to both for your thoughts. I’ll do it that way. 

Mol