materials wont apply - always grey object

I have a ceiling on a room that i've modified to have a lighting trough around the edge of the room. No matter what material I apply to the object it renders as default grey - everything else in the dwg renders fine. I cant remember exactly how i modeled the ceiling - its definately solid modeled as a 3d solid so the the 'skin' should be on the outside. What could this problem be??

had you just done a linear map of the ceiling?

Have you tried adjusting the tiling and scale of the ceiling material? Maybe it's tiling so small that it just appears grey.

maybe its something to do with lighting. will take a look