Cutting a mesh in half

I have a mesh which I have imported from an OBJ file. I would like to apply Material A to the section of the mesh which is on one side of a given plane, and apply Material B to the section of the mesh which is on the other side of that plane. (A potential plane is indicated here as a blue line.)

To do this, I need to split the any faces which intersect this plane, and select all faces on one side of the plane so that I can apply a material to them. How can I do this in the current versions of Blender?

I’ve tried using the knife tool (K) in cut-through mode (Z), but the cuts haven’t been reliable. Even when they were, after the cut was finished I couldn’t figure out how to select only the faces on one side of the cut. (The details were too fine to be reliably selected with any tools I know, such as the circle select tool ©.) I tried using the rectangular selection tool activated by pressing B, but it only selected the faces on the near-side of the mesh.

We used to have a procedure to cut a mesh using a plane in Blender 2.4, but it involved using mesh boolean tools which appear to have been replaced, and I can’t figure out how to adapt it.

You could use the bisect tool. Mark a seam along the cut line, then in face select mode use L to select linked faces


go int the ohrto view,and then press z,then with b select the one side for the material 1,go to the materials panel,add a material,call it material 1,apply it,than deselect the half,and select the other half,go to the material panel again,and add another material,call it material2,apply it and there you go :).need video?.

Any serious reason why you want to stick with this, instead of using blender to make usable mesh in 5 minutes?

I give it under 1 minute. except for the monkey.
(edit) in previous versions, the knife tool could do this, but i think it lost the ability in recent versions.

@Modron: One still have to figure how to make Bisect and Subsurf play together and how to not allow to stretch materials… more or less… I keep it 5 ;).