Odd Non-Planar(?) Face

Are these:

called Non-Planar faces? How do you fix them? When modelling with quads, this seems to happen a lot, especially with proportional editing on. When a solidify modifier is used, it draws a weird border around the quad. Why is that? How do you detect these in blender?

- Solidify example

you can’t fix them except by converting them to triangles. otherwise just try to avoid them by placing your edge loops carefully.



Flatten faces tool, (See menu: Mesh -> Cleanup -> Make Planar Faces)

Thanks! I see that flatten faces tool, and it might work, but how do you convert to triangles? Is it a modifier or something?

command: ctrl T