My advice is make it on layers...
First step is to make the first background layer, start directly with the color. What you are trying to do is to use the same color evenly for the complete surface. Once you get this you can add some gradient effects easier.
You need to mix the color before you put it in the AB, such that is evenly sprayed. for big surfaces I use normal acrylics (see here how to mix
) Keep the proportion of the mix for you to make more after if needed.
- Mask (cover/protect) what you don't want to be painted and cover everything that goes in another color or can be contaminated. Take special care on this.
- Use thicker paint for the first layers (less water), high pressure and more diluted second layer... put as many layers you need to make it even.
-Follow an order, keep the distance to the canvas always constant, and move at constant speed.
-Don't stay too much in a spot, overspray, or put too much paint that it drips. Wait a bit between layers, let them dry before you add the next.
-Do not use the AB too close or you'll make texture or damage/remove prior layers. Its better to be further than closer.
-Use as much paint as you need... You'll be surprised how many times you have to pass to make it look constant.
This is an example: 1.5x0.5 m, the blue sky is airbrushed and is perfectly flat with 1 single color: