Not done Mid-Surface mesh-add thickness to the elements

Hi,

I did shell mesh by extracting the elements from Tet mesh. Technically they should be connected, just for ex: a cover(shell mesh) on a solid part(Tet mesh). So here I did not extract any mid surface. How should I add thickness here? I am sure mid surface thickness is not going to work. I tried with Mid-mesh thickness as well, it di not work. Could anyone please suggest