i want use de decimator modifier but i cant…
a message apareace…
this is no a manifold!!
what is and how fixed or change???
thanks
sorry my english
I’m sorry I can’t help you, I’ve never seen that…
SOMEBODY HELP HIM!!!
erhhrer…err… you are welcome. 
Manifold is like a closed mesh = no holes. For example if you cut a Sphere in half and chose to Select ‘Non-manifold’ = it would select only the diameter. That help?
In general: A non manifold mesh has edges that belong to more than two faces.
Often you either have a Y shape in your mesh, or inner faces. Inner faces are often the result of extrusions or joins.
How to fix? Find the wrong edges. This is not so difficult. Use a subsurf modifier, make sure you klick “set smoth”, and recalculate normals. Change to shaded view. The black stripes on your mesh indicate where the problems are.
A non-manifold mesh is one where an edge has more or less than 2 faces attached to it. The decimator can handle the one face per edge case but can’t handle the 3 or more situation. You will have to delete interior faces for the decimator to work.
GreyBeard
Finding non-manifolds is even easier: In EditMode unselect everything and click menu ‘Select’ and then option ‘Non-Manifold’.
JaMB
Neither method worked for me. Select Non-Manifold selects nothing. Adding a subsurf modifer shows nothing out of the ordinary. Yet the decimator still claims I have a non-manifold mesh.
can you upload your blend somewhere?