Thank you Gaieus, Remus and Anssi, It's surely the co-planar surface problem (Z fighting) since I remember re-drawing the same surfaces somewhere. Will re-examine the drawing and find out. Thanks a lot Bye Mario

Thanks a lot Jim, you'll have understood that I am a beginner with Sketchup. Have already tried your suggestion and solved the problem. I understand that Dynamic Component is supplied with the more professional Sketchup version and would make things easier. An incentive to purchase in the next future I hope. Bye Mario