Gunpla Painting Exercise: Water vs. Alcohol Paints & Primer Test

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If you want your model kits to have a flawless, professional finish, understanding the theory is only half the battle. Now, it is time to put paint to plastic.

In part two of our Gunpla 101 series, we are diving into a hands-on Gunpla Painting Exercise to test exactly how water-based products hold up against alcohol-based (Aqueous) products. From the initial prep work to the ultimate masking tape adhesion test, here is everything you need to know to prevent your paint from chipping.

1. Preparing Your Plastic for Paint

Before you even think about loading your airbrush, your plastic needs to be completely prepped and clean. Skipping these essential steps will instantly ruin your paint job.

  • Washing the Runners: A tiny speck of dust hidden in a crevice will completely mess up your primer. Washing your plastic in an ultrasonic cleaner or with soapy water is absolutely necessary.
  • The Drying Phase: Cleaning is important, but drying is critical. Leftover water droplets will prevent the paint from bonding to the plastic. Always use a cotton swab for detailed drying in tight corners.
  • Sanding for Water-Based Primer: If you are using a purely water-based primer, you must sand the pieces first. You aren’t trying to grind the plastic away; you are just using an 800-grit sponge to rough up the surface so the primer has something to grip. This step is tedious but mandatory for water-based bonds.
  • Gap Filling: For annoying molding lines or gaps, use Tamiya Epoxy Putty. Mix it one-to-one, apply it to the gap, let it cure for a full day until it is as hard as plastic, and then carefully sand it flush.

2. Airbrush Setup & Spraying Technique

Having the right gear is great, but using the correct technique is what gets you that buttery smooth finish during your Gunpla Painting Exercise.

  • The PSI Settings: Following the Badger airbrush instructions, I highly recommend using a 0.5mm nozzle and setting your compressor pressure to roughly 28 to 30 PSI.
  • The Pulsating Technique: Never try to cover the entire piece in one heavy, wet press. Instead, pulsate the trigger. Your first coat will look like barely visible dust. By the second and third coats, you will start seeing the solid color build up cleanly.
  • Mixing Custom Colors: When mixing a custom off-white, I combined pure white, a drop of gray, metallic flakes, and water. However, I found that alcohol-solvent paints (like Tamiya and Aqueous) sprayed much easier and nicer than purely water-based Gallery colors.
  • Inner Frame Painting: For the inner frame, I used Tamiya acrylic gunmetal pre-thinned with lacquer leveling thinner. It surprisingly worked incredibly well and didn’t smell like a harsh lacquer spray.
  • Immediate Cleanup: Since I paint in my room, cleanup is highly important. You should thoroughly clean your airbrush immediately after use so the paint does not dry and get permanently stuck inside the nozzle.

3. The Ultimate Gunpla Primer Test

This is the most important part of our Gunpla Painting Exercise. We tested the bonding strength of a sanded water-based primer against an un-sanded Aqueous (alcohol-based) primer.

  • The Masking Tape Test: After letting the primers cure, I applied standard masking tape directly to both surfaces, rubbed it down hard, and aggressively ripped it off to simulate complicated masking work.
  • The Water-Based Failure: Even with prior sanding, the masking tape completely ripped the water-based primer right off the plastic.
  • The Aqueous Victory: The Aqueous primer, which had absolutely zero sanding prep, held onto the plastic perfectly. There was no chipping and no peeling.
  • The Final Verdict: If you are just doing a simple color swap, water-based primer is fine because it smells less. But if you are doing complicated masking for two-tone color separation, you 100% need to use Aqueous primer.

4. The DK Hobby Hack: Mixing, Masking & Details

Building Gunpla should be fun, not frustrating. Here are a few rapid-fire hacks to speed up your workflow.

  • Metal Mixing Balls: When transferring thinner or mixing custom paints, drop two small stainless steel mixing balls into your paint bottle. It drastically helps mix the pigments and residue at the bottom.
  • The Tape Trick: Never put masking tape straight from the roll onto your painted Gunpla. Always stick it against your skin or a cutting mat a few times to loosen up the extreme stickiness.
  • Gravity Leveling: When using slow-drying enamels (like fluorescent green for Gundam eyes), clamp the piece parallel to the ground. The enamel will naturally level itself out using gravity as it slowly dries.
  • Decal Painting: The HG Demi Trainer comes with swappable chest stickers. Instead of spending 30 minutes masking the entire chest piece, I just painted directly over the stickers using a Gundam marker and enamel green.

Gear Mentioned in This Lesson:

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