How to thicken a twisting solid

I have to add thickness to the walls of a twisting solid on the top of an arch and need help on how this would be done. Below is an image of the piece which is twisting in several directions and I need to add 1/2" of thickness to the back of the object. I have tried every type of offset that I can think of, but nothing is giving me the correct geometry. Basically, I need the back of the piece to extrude normal to the back surface, but I can’t get it correct.
Can anyone offer some suggestions?

Hi Stephen - OffsetSrf or Shell is what comes to mind , depending on just what the goal of ‘thicken’ is. It’s possible there will be some cleanup to do, depending on the complexity of the object.


I tried OffsetSrf, but I don’t want it thickened in all directions. It’s a piece of stone and the left side and the bottom are visible. The right side and the top of the “L” shaped profile are the thickness of the stone and I need to change that thickness from 1 1/4" to 1 3/4". I can’t seem to find a way to offset just the “back” faces of the piece without exploding it first.
I’ll try to play around with Shell to see what I find.