Hi Ricardo, yeah something like that is not going to get thickened automatically, in particular areas that are very tightly curved in a small area like this spot you have here are problematic:



What thickness are you trying to make?

The most basic starting point is to use Edit > Separate on the object so that you have all individual surfaces and then run Construct > Offset to generate offset surfaces of those. That will then give you a bunch of surfaces to work with, many of which will need to be extended areas built or trimmed with other surrounding surfaces.

For areas where the surfaces are all smooth to one another and don't have super sharp hooks like the above, you can leave those areas joined together and offset them as a connected object.

Another area that will cause difficulty is the degnerate corner situation that this surface has - it's not good to build a 4-sided surface with 2 of the sides tangent to one another, it makes for an indistinct corner which can easily be folding back over itself a slight amount making for a chaotic surface normal in that area of the surface:




Probably the actual easiest way to build a thick result from this would be to import the model into a different CAD program that has a better thickening mechanism in it, but that particular surface above will probably complicate the transfer into a different program too. That's the same surface that has the sharp hook on it also so you may need to actually reconstruct that particular surface to be better quality as a first step.

- Michael