Normals are fine, but I still see missing faces from my Blender model

So I made a model in blender (v2.70). All the normals are facing the proper way (I did the recalc normals thing in blender) but when I import the model into Unity there are tons of missing faces. How can I fix this?

Most of the suggestions I’ve seen are some variation of “flip the normals back and forth or recalc them until they work” but I’ve already done that with no luck. Thanks!

You likely have Non-Manifold areas in your Mesh. This can cause missing geometry.

Select your mesh object alone (Blender)

In edit mode, De-select your whole mesh then click Vertex mode. Click Select Menu → Non-manifold.

Manifold mesh is water-tight, hollow mesh.

Non-manifold is caused by holes in your mesh and internal edges. If you have used Vertex Snapping to connect two edges together in a T, this is a prime suspect; They are not joined properly, just placed.

You will probably need to Remove Double Vertices also.

Have you turned on the view normal in blender and just made sure that the recalc worked. I have seen cases where I had to manually change the direction.