Acrylic Paint Issue

[Mark Aldrich]

OK Acrylic Warriors, what did I do wrong? I was attempting my first hair spray chipping technique. I used Model Master Italian Olive Green as the base. I then sealed it with three coats of Model Master clear flat. I then applied three coats of hairspray. This was followed with Model Master Acrylic Radome Tan and in numerous spots, the tan paint cracked. This might be a blessing as these will be obvious places to apply the technique, but I wanted to decide where they should be, Any ideas or thoughts on what I did wrong?

[Ron Bell]

That's usually a sign of disparate drying, meaning the coat on the top dried before the coat on the bottom. When the bottom coat shrinks a bit as its carrier dries, since the top coat is already dry it can't accommodate the change and it cracks. You've got four coats to deal with. I'd start by letting each coat thoroughly set, not dry, set.

 

Another problem is an acrylic/oil/lacquer interaction. You can paint acrylic over anything, but don't put oil over acrylic or lacquer, or lacquer over anything except lacquer or you risk an interaction such as bubbling, cracking, peeling or just not adhering. An exception is you can spray lacquer over other paints as the thinner mostly evaporates before it touches the surface. However, spray it too heavy and you'll get the above effects. Check all your paints to make sure they are compatible. I know more than once I have purchased MM paints thinking they were their oils but then found out they were their acrylics. Very similar labels in some cases. Also check the hairspray. Some are alcohol based, some not.

 

In some cases, these effects can be beneficial. Since acrylics don't adhere well to much of anything and never really set hard, they are good to use over oils or lacquers for chipping effects as they can be easily "chipped" off leaving the under color showing.

 

Others may have more specific advice, but I've found these are the usual suspects in my screw ups.

[Mark Aldrich]

Thanks Ron. Among other issues, I guess I am supposed to use gloss to seal the undercoat. It turned out decent for my first attempt. Think there is too much paint on things like the tools. Sure it will get better the next time I attempt it.

[BryanKrueger]

A gloss coat between paint and HS isn't always necessary. It depends on the effect you are after. The HS technique has a lot of variables.

 

One of the most critical is how thick the top coat of paint has been applied. If the water can't seep through the top color, it won't reactivate and loosen the HS.

[pmhayward]

Dido Bryan. I had an issue last year with trying the same chipping technique. I would wait atleast a full two days between coats. That way all the de-gassing and drying can occur.

[BryanKrueger]

I airbrush with Tamiya and always thin with their laq thinner. I usually wait a couple of hours and then apply the HS. I've pushed it to 15min but then I run the risk of rubbing the Tamiya paint off high spots when I'm scrubbing. I've never had problems with layers reacting nor cracking.

 

For the HS I use Tresemme (sp?) Ultra Fine Mist. If I'm in a hurry I shoot from the can - 2 light coats are usually enough for most light scratches. 3 if you are chipping off large chunks. If I only need to chip certain areas or want to control the amount of HS, I decant the HS into a jar and use my AB to spray the HS.

 

The HS chipping effect is one of those techniques that needs a lot of practice and personal experimentation.

[Mark Aldrich]

Thanks guys! I am not a BIG weathering guy. I rarely do it so it will be sometime before I try again.

[Highlander]

In general, I have found that you should let any coat of anything you put on a model dry for at least 24 hours. 72 hours for oils. The problem usually is that you don't want to add weeks to a build just letting stuff dry. So you find ways of speeding things up. Often by reducing your wait time for drying. As I'm doing right now on a 1/72 scale Sherman's clear coats, which I've let dry for as little as three hours.

 

You don't have to do this, but you should. You can learn your materials and develop techniques where you don't need to, but you should. Because, eventually, you will discover that you really should have.