GW grey spray - primer or not?

[Lazaris]

Hi everyone,

I bought a can of Mechanicus standard grey spray at my local GW shop, and I intended to use it as a primer, but it just came to my mind that it might not be one...

I checked online, and people seem to disagree: half of them say that you need an undercoat (a black primer I suppose?), the other half say that they used the grey spray straightaway and it worked.

Sooooo, can I have a clear answer? Pretty please?

Thanks!

[Patriark]

I use mine as a primer directly on plastic and resin miniatures and it works great! Note though that the colour is exactly the same as GWs unpainted plastic, so it's quite difficult to se what areas of your plastic minis that have paint on them. For that reason only I would consider a black or white primer as a base. 

[Sheriff]

I thought it was primer... seems to work fine. Only model i had issues with was fine cast but i think that's just fine cast being fine cast. 

[Spiky Norman]

I used mine as a primer and it worked just fine.

[Lazaris]

Thanks for your answers! I tried and I can confirm it works fine!

[merzbau]

It's weird how about half of GW sources (Duncan, various studio painters in White Dwarf, etc) say it's fine and half- presumably out of an excess of caution- call for a primer coat underneath. I was wondering the same thing lately (especially after a staff painter in the, IIRC, January WD noted that the sprays are "solvent based" and thus suitable for undercoating) and was planning on running a few tests on spare models to try it out...

[RuneBrush]

I can confirm that all of the current range of GW sprays work perfectly well as a plastic undercoat/primer layer onto bare plastic.  Have used probably half a dozen different colours recently and all solid as a rock.  The previous range were very hit and miss if you used them like that so this is likely where some of the confusion has come from.  What I would say though is that the lighter/brighter colours benefit from two or three light coats rather than one thick one (whereas Chaos Black largely you can get away with doing in one) and if you want a really bright (or dark) colour, then using Corax White (or Chaos Black) will help you adjust the brightness.

[Trokair]

I have used the Grey spray both on its own and with a black primer underneath. It seems ok on its own though two thin coats are better. 

The manager at my local GW told me that the chemical composition of the coloured spray is a bit different from the black and white primers and that it has less of the binding agent that makes the paint work as primers.

[Killax]

You can use it however you like. In my 15 years of Wargaming Ive never had any paint chip off plastic models. Because GW's line is currently almost completely plastic I'd say you will do fine with either option. If you do go for a black undercoat first you might aswell get a small advantage by painting it in a "zenithal way" with grey but at the same time that advantage really remains only if you intend to paint with thinner coats of paint, close to glazing, akin to washes. 

In the case of "white metal" and resin models I have had models who's paint chipped off. For "white metal" and tin models the acryllic properties of paints simply said are less ideal, yet most people prefer to paint with acrylics because most shops carry these kinds of products. For resin models the only reason why chipping has occured for me either had to do with cleaning the model incorrectly (too fast) or the actual model being damaged.

So far as I know there is no difference in chemical bond between any of the sprays and because they are all acrylic sprays they match a lot of the pvc properties the models have and thus are ideal to be used in combination. 

TLDR: You can use Grey as a prime coat just fine, there are advantages you can obtain by essentially pre-shading/pre-highlighting when you use Black first and pre-highlight with Grey. I use Black first and pre-highlight with white. As white is ideal for a caucasian skintone and brighter colours.
Grey is ideal for more natural colours as brown, green and blue. Black actually is less ideal but speeds up the 'shading' most people have difficulties with getting right.