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Just started using my airbrush to prime some plastic GW models with Vallejo Primer. 2 days later and I'm able to easily scrape the paint off by scratching with my fingernail. I can't remove it without scratching, so it's not like it's just falling off or anything. Spray can primer is usually almost indestructible so I don't know what to expect from this. Just wanted to check if this is normal and if the models will still withstand normal gaming and handling after I finish and prime them?

I've found the same with the Vallejo airbrush primer, specifically the grey one (haven't tried the others). It is kind of rubbery and scratches off easily.

Not sure how well it lasts as I rarely get to play a game so my models are not handled/transported that often.

I have stopped using it though, in favour of the Army Painter coloured primer sprays these days.

Sorry if that doesn't really help much, but just to confirm that I have had a similar experience. Hopefully some of the more seasoned P&M Dakkaites will chime in soon.

Yeah I stopped using Vallejo primer because it's not tough enough for my liking.

If you make sure the model is cleaned with soap and water before painting it, apply a couple of thin layers and don't let it build up too much and then wait plenty of time for it to cure (a couple of days), then it gets tougher..... but it still sucks IMO. If you follow those precautions with other primers they will be even stronger again.

Aerosol primers are usually the toughest. The toughest non-aerosol primer that gives a good base for acrylics that I've personally used is Gunze Mr Surfacer, but it's a lacquer which can be a little bit annoying and it's still not as tough as a spray can primer.

I've been meaning to try Humbrol enamel primer (the one in a pot that you can airbrush on) to see if it makes a good base for acrylics. Enamels are tough, when I'm using enamels I often don't bother priming, so it makes sense that an enamel primer would also be tough, BUT, in general the surface of an enamel is low surface energy thus acrylics don't like to stick to it.... I need to test whether this is also true of the primer or whether it does form a good base for acrylics. Enamels also take longer to cure to their full strength.

Tamiya acrylics when thinned with a lacquer based thinner are also quite tough, but I haven't tried using them as a primer.

I've also been meaning to try decanting some Tamiya spray primer in to a bottle and trying that. It's also lacquer based and although it's expensive if you plan on just spraying it from the can, but if you decant it out and airbrush instead, it actually works out quite cheap.

After reading skink go on about Mr Surfacer, I caved and got some.

It is an order of magnitude better than Vallejo PU primer

Also, My Self Leveling Thinner is the perfect thinner for Vallejo liquid metals. Such a good day

Just some thoughts on various primers.
On the subject of Vallejo primers;I started using them when I was building model plane kits.I found as long you wash the plastic it has no problem being applied,yes it is not tough but to be honest you should not be trying to scrape it off anyway! Handle all primed models carefully.The same goes using it on plastic and metal models;just avoid over handling them during painting. I should point out that I brush it on,maybe airbrushing makes it less durable?
On enamel primer; It is a bit of a myth that has been allowed to grow over the years.As long as it is dry before painting over it then acrylics will have no problem sticking to it. I would suggest using thinner with enamels,the grey primer that humbrol do is on the thick side. Also matt black is good for priming(thinner),there are many people who do use enamel for priming,top British painter(he paints for Wargames Foundry),Kevin Dallimore,uses matt black enamel most of the time and paints with acrylics over it. I have 2 original Land Raiders that I primed with matt white enamel way back when they were released and after all this time the acrylic hasn't peeled/cracked/flaked.
Try them,you might be surprised. It does screw up your brushes though,so buy some cheap ones!
Hope this helps.

kb_lock wrote:
Also, My Self Leveling Thinner is the perfect thinner for Vallejo liquid metals. Such a good day

You mean those alcohol based metallics? I had no idea the self levelling thinner worked on those as well. Do you airbrush them or is that just for hairy brush painting?

Slipstream wrote:
On enamel primer; It is a bit of a myth that has been allowed to grow over the years.

Well when I said "BUT, in general the surface of an enamel is low surface energy thus acrylics don't like to stick to it", that wasn't based on on perpetuating a myth so much as observations and experience. I use Testors Model Master enamels quite a lot, I quite like how they behave when airbrushing them. I've noticed that when I paint acrylics over the enamels the enamel clearly has a lower surface energy, lower surface energy = acrylic doesn't spread as nicely over it. Even if the enamel is a matte finish it's noticeable. The acrylic is also more prone to rubbing off, which I think is due to water based acrylic relying on surface texture and surface energy for adhesion (unlike something like a lacquer or some alcohol based acrylics which have strong solvents that actually bite in to the primer).

Yeah the alcohol based metals, never tried airbrushing them, only with a regular brush. I used to thin with IPA, which helped but was far from perfect. This stuff is beyond perfect, makes using the liquid gold so much more palatable.