Earth soda bottles

Has anyone found a use for 2 soda bottles?  I was thinking about filling them with some kind of soil/sand mixture, possibly painting them or covering them with some kind of coating to make them last longer and then using them as bricks to make walls, etc.  Any ideas here?

Yes, we have done that with plastic soda bottles. Not 2-litre size, just normal serving size, whatever that is, like maybe 500 ml or 700 ml? Huge numbers of them wash up on the riverside near our school. We filled them with sand/soil and used them as bricks to build up the sides of the raised beds in one of our greenhouses. I thought they'd disintegrate in the sun within a year, but actually they didn't and have lasted several years now. I guess the greenhouse plastic glazing keeps enough UV out. They are squashy though, and the walls have deformed. Doesn't matter in this application, but wouldn't be good in the wall of a building if that happened.

If the bottles were painted or coated, would that make them last longer?