Assigning materials to objects from blender

so I imported a few objects from blender which didn't have any textures or materials on them and then I decided to put a material on them in unity. However, parts of the object have the material assigned to them while other parts of it are grey. If anyone knows a solution to this, please help. update: found that the material texture thing covers such a small area that you can't see it and it all just looks grey. is there a way to solve this, apart from lowering the amount of detail in the object?