i have a surface piéce and i want to rebuild it as a volume piéce

Can you attach the *.sldprt file here?

You can turn a Surface into a Solid by using the Thicken command.  If the Surface is completely closed, there is an option to turn the enclosed volume solid in the Thicken command.  If the Surface is not completely enclosed, you will have to define a thickness for the Surface.

Attaching the model is always a good idea when you can.