Interior Paint 4


This post covers three shorter workshop sessions. In the first two sessions I removed the contaminated paint with sandpaper. You can see the results of this here. I used 400 and 600 grit sandpaper to achieve the desired results. In retrospect I would recommend using only 600 grit or higher. (The paint data sheet calls for 400)

I needed only to repaint the areas that were contaminated with improperly mixed flattening agent. Mainly about half of the parts and the rear seat back bulkhead. Here you can see the parts after sanding.

And here are the parts after painting. 

The humidity when I arrived was over 70%. Turning the fans on and opening the barn up quickly dropped the humidity.

I bought mixing cups and paint stirrers from Amazon. I was not going to have a repeat of the last performance.

My method for mixing the paint is below.

I couldn’t be more thrilled with how the paint turned out today.

Tips for painting with a single stage and a flattening agent:

  1. Air supply:
    1. Compressor: I have a large oil-less portable compressor that can handle the volume adequately. It is a 33 gallon husky that can handle 5.1 SCFM at 90 psi. Ideally you’d want the largest compressor with the highest SCFM you can get. I opted for this model as it runs on 120VAC and can be somewhat easily transported. For an HVLP gun running at 20psi it’s more than sufficient.
    2. Filters: I have three filters between the compressor and the gun. The first is at the compressor exit. This filters particulate well, but being so close the compressor means it does a poor job of removing moisture. Next, after 50 feet of hose, I have a home-made dessicant dryer. You can see the details of that dryer here. Finally, I have a disposable inline filter at the gun.
  2. Ambient air:
    1. Dust free: I have done my best to create a paint booth that can ensure I have clean dust free air inside. I have used two fans and HVAC filters to achieve this. It is not perfect. For more details on my paint booth check here.
    2. Humidity and Temperature: I have no way to control humidity or temperature in my paint booth. I have a temperature and humidity sensor in the paint booth and I do my best to achieve a temperature greater than 70 degrees F and a humidity lower than 50%. The warmer the temp, and the dryer the air, the quicker the paint will dry.
  3. Mixing with a single stage:
    1. Thoroughly mix your paint and flattening agent using a drill mixer. Do not rely on hand mixing no matter how thoroughly you think you have it mixed.
    2. Combine your paint with activators and hardeners as necessary.
    3. Combine activated paint with flattening agent via a cone filter. Mix thoroughly again using a drill mixer.
    4. Transfer the mixed paint to the gun again via a cone filter. It is vital to ensure the flattening agent has thoroughly mixed and that any clumps are filtered out.
  4. Paint Gun:
    1. Setup: I use a 1.2mm tip for single stage paint. For priming I use a 1.8mm tip. The compressor tank is pressurized to full capacity (approx 165psi). I then step this down to about 60psi exiting the compressor. I then step the pressure down again at the gun to 20psi. Your numbers will likely vary, but here is the goal. The gun should have 20psi at the inlet. If you use a regulator at the gun it will have an initial residual pressure greater than your setting and the initial burst from the gun will be at a greater pressure (for a fraction of a second). As you continue to hold the trigger, the pressure will fall to an even pressure. I play with each of the regulators to do two things. First, ensure that with the trigger pulled and held the pressure remains 20psi. Second, that the difference from the initial trigger pull to even pressure is as minimal, or nonexistent as possible.
    2. Use: Its imperative that you spray perpendicularly to the surface at a consistent distance and at a right angle to the surface. Here is a great video from Eastwood on painting technique.
    3. Cleanup:
      1. Remove remaining paint
      2. Add acetone to the spray cup. Swirl around and shake cup. Spray a portion. Dump acetone out. This will remove the majority of the paint.
      3. Add a second set of acetone. Swirl around and shake. Spray this acetone through the gun. Vary all the gun settings as you do so. If step do is done thoroughly, the spray in step 3 should be almost clear.
      4. Break the gun into all its components and clean with brushes, acetone, and rags every crevice, hole, and surface until it is free of paint.
      5. Store tips, needles, and components in acetone.
  5. Working with flattening agent: The flattening agent is a suspension of what is basically a white chalk. When dried without mixing it makes a flaky chalky mess. The mixture is very sensitive to proper mixing. Additionally, the amount of spray will affect the gloss level of your paint. A light coat will appear more flat, and a thick coat will have more gloss. As a result if you are uneven in your painting technique, your result will have varying amounts of gloss. It is critical with a flattening agent to do three things.
    1. Ensure a consistent mixture ratio
    2. Mix thoroughly before mixing with the paint, and after mixing with the paint. Use a cone filter before placing in the gun, and use a filter at the bottom of your paint cup!
    3. Spray evenly and consistently!

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