Q. My company makes plastic parts for various industries, and one of our customers has complained about cracking of an ABS plastic part. My question is about the structural strength of the coatings. One of our engineers has proposed that we coat the plastic part using a paint of the same color, believing this will increase its strength, prevent cracking and maintain the same appearance. Do you agree with this? K.W.
A. You can paint ABS plastic parts the same color as the substrate to maintain their appearance and to prevent minor surface crazing, but no paint will increase the strength of an ABS plastic part to prevent structural cracking. Paints are usually applied at thicknesses of 1 to 3 mils (0.001 to 0.003 inches). If the substrate cracks, the paint will crack as well.