Humbrol Primer

I'm not sure if it is just matt grey or not, but in my experience, the Humbrol primer is no good, so I would not recommend using it anyway

Simon,
Humbrol Primer isn't in my paint box - I've never used it - I often use automotive acrylic primer.....sounds scary, but I've found that it works really very well. Etches the plastic, provides excellent "tooth" for the color coats, dried REALLY quickly, and no model paints can harm it, so you can spray ANYTHING over it.
For simple structures and builds, it's great - but it can slightly attack areas that have a lot of filler, making the filler show up. In that case, I useModel Master primers like light greys and flat white. They work really well and I've never had any problems with them.

I use Humbrol primer for all my 1/12 Tamiya f1's and think it is a great primer for that purpose. You must allow it to completely cure (i give it a week or so)....once it is cured it is practically inpenetrable. I use Duplicolor laquers over the top with excellent results. Hard finish and great to polish. The thing i like most about the Enamel primer is, if i stuff up the top coats, i can just soak the model in Oven cleaner for 24 hours and it simply dissolves the primer underneath, letting the Duplicolor "peel" off like a sheet of skin!!....much less mess and the plastic is back to it's original flawless condition

I used humbrol primer for a while and it was OK for my uses. Just a bit thick for a good primer. I use 50/50 Mr. Surfacer/Lacqaur thinner now with much better results.
Jeff

Some place years ago I got the impression that Humbrol Primer was orgionaly developed for metal figures especially lead (apparently if you painted lead figures without priming them, they would corrode under the paint, ruining the surface).