I am painting interior walls that have old textured surfaces and rough surfaces. How do I smooth them out?
Answers:
Paints for external use did contain sand (i.e. Sandtex) but most internal paints and coatings used plastic/resin granules. You really need to remove this completely for best results. However, if you are just patching-up the surface you need to use the same textured paint again on the repaired walls to make them match.
Other answers:
sand it
sand it
Maybe you can get a power sander and sand the whole wall to your liking...
Use a fine grade sandpaper to smooth out the rough spots. Go easy on the surface though. If you want to add texture you can buy it in cans at the place where you purchase your paint. You just roll it on like paint. Or you can have someone come in and spray texture on the walls/ceiling for you.
This is why people like textured surfaces. They hide all the imperfections.
Most of the texturing stuff can be removed very easily with a putty knife. It WILL be messy. Putty knife doesn't need to be sharp.