The PLA hull was sanded down starting with a heavier P150 grit sandpaper. After that I switched to P220 and finally P320 to get the hull as smooth as possible. After I started sanding I soon realized that PLA is much less forgiving then I realized. It took approximately 3 hours to sand the PLA to a desirable smooth surface as see in figure 1.
Figure 1: Sanded PLA hull. Roughness can still be seen.
Once the hull was cleaned of any dust and debris the next step was applying a thin layer (no thicker than 1/16 inch) of “3M Acryl-Green Spot Putty” as seen in figure 2. This was done to fill in any imperfections left on the hull. The putty was applied using two pieces of construction paper which allowed some flexibility for the curvature of the hull. A respirator was also used to combat the intense odor of the putty (application should be done in a well ventilated area).
Figure 2: Spreading green putty over hull.
After I let the putty dry for 2 hours (directions only say 15 minutes) it was time to sand the hull again. Just like the first time, I started with a heavier P150 grit and worked up to a finer P320. The second sanding process took about 2 hours in order to get the surface where I wanted it. Minimal blemishes need to be buffed out, but so far I am very happy with the way the hull has turned out.