Shapeways printed parts must be cleaned and primed before assembly and painting. This post explains how to clean and prime Shapeways parts.
Cleaning parts
Shapeways prints a waxy support material wherever support material is necessary. You should remove this waxy support material so CA adhesive can be used to assemble and attach parts. Parts also need to be cleaned before they can be primed and painted. You should clean parts in an ultrasonic cleaner with some Simple Green in warm water. Then rinse parts with clear water.
Priming parts
Shapeways printed parts have some striations on what should be smooth surfaces due to the limitations of the Shapeways 3D printing processes and material used. After cleaning, the parts should be primed with a primer containing fillers like Mr. Primer Surfacer 1000 or Tamiya Fine Surface Primer to make the surfaces smoother. A number of thin coats from a rattle can should be applied.