to prime or not .........

I'm currently conducting an informal experiment, spraying 24 different metallics (15 Alclad II, 9 ModelMasters and Testors enamels) over 9 various colors of undercoat.  i', 2/3 finished, and so far I've found that some Alclads are more transparent than others, and the base color shows through.  This is particularly so with Titanium Gold.

Alclad high-finish colors (chrome, polished aluminum) must have a high-gloss black undercoat to get the depth of reflection.  For most of the other colors, the critical factor seems to be the surface of the undercoat: the glossier the surface, the shinier the finish metallic coats.  The Aluminum variants cover well, but the surface will be affected by what's underneath.

An "primer" coat of Mr. Surfacer 1000 or 1200 provides two big advantages: 1) it provides an even surface color over any material, which should help with the more transparent metallics,, and 2) it shows up any flaws in filling and sanding so you can rework them before applying the metallic.  It can be polished with toothpaste or automotive rubbing compound.  Be sure to clean the surface thoroughly before shooting the Alclad.  Mr. Surfacer isn't called a primer but rather a filler. However, it has served me well in both applications.

For Chrome and Polished Aluminum I shoot Alclad II Glossy Black Base Coat or Scalecoat Locomotive Black (with Scalecoat's dryer added) over Mr. Surfacer.  I haven't used Future as an undercoat, though I noticed some Alclad labels recommend it.  It would certainly provide an ultra-smooth surface for the metallics.

Alclad contains MEK, and will craze enamel (and perhaps some acrylic) undercoats.  Future could provide a good barrier to protect them.  Always wear a respirator, especially when working with such nasty solvents as MEK.

Hope this helps.

" I haven't used Future as an undercoat, though I noticed some Alclad labels recommend it.  It would certainly provide an ultra-smooth surface for the metallics."

I've used Future as a basecoat on my last three NMF finishes and it works great. It does provide a very smooth surface. I haven't used the hi-finish Alcad colors so I can't comment on those. I'll be using the regular aluminum and dark aluminum colors, which I'm familiar with and have used. My concern here is a color difference between the resin and grey plastic of the "raw" materials after I apply Alcad topcoats. My instincts tell me that I'll need a uniform color to have the Alcad look the same over the entire model when finished. I don't have Mr. Surfacer 1000 or 1200 and plan on using MM grey primer if I need a primer at all. I don't know if Future will take care of that color difference between the mediums or if I need to prime it first then Future it before the topcoats. Thanks for your information, it is very helpful but I 'm still not sure about which way to go here. Thanks again.

Hud

prime it.  better than  having the top-coat chip off later.

I prime everything, especially when using dissimilar materials that have to have a smooth transition between them. It's not so much a matter of uniform base color as to help the eye see imperfections in the surface. It's too easy for the mind to attribute the seam between resin and styrene to the difference in color, when there really is a seam that needs to be fixed.