Is there a way to hatch all the faces wich are facing to 1 side, up or down?.
I have a object wich isnt thick enough to select all faces, but they have to be an other colour than the object
directly above this side.All are single lines and faces, i can not make groups or components.
Switch View > Monochrome [switches of any applied materials]
With a Style which has a distinctive back-face color you can clearly see the front and bottom faces.
Typically the default Style colors are off-white & blue-gray.
If NO faces are oriented the correct way, then treble click to select all faces and Right-click > Context-menu > Reverse-Faces… All faces should then ‘flip’.
However, if some faces are already correctly oriented, Select one face [single-click] that is orientated the right way.
Right-click > Context menu > Orient Faces…
Any connected faces should now be reoriented to the same direction.
This should work on your simple 2d surface, or a more complex ‘solid’ 3d form…
Change your View type back to show materials…
Repaint any reoriented faces that are now wrong…
It’s hard to tell from your dark screen shot but it looks like there are a lot of edges dividing the surface. If you soften those edges you can paint one side with a single click of the Paint Bucket.
In this case I temporarily softened the edges on the low ridges since they aren’t rounded over.
Thanks, that works great. 
Thanks for the message, i will look into this.
