Reversed normals

[mmodernc]

I imported a surface that had been created in Datacad, converted to dwg then imported into Revit as a mass that was then converted to a curtain system. The problem was that the normals on nearly half the polygons were reversed and therefore the thickness of the curtain panels went the wrong way. It is possible to use the handles of each panel when selected to drag the faces into the right way. Is there a way of aligning normals in Autocad. I know that you can do it in Viz but you cannot save the model back to AutoCAD.