Every wall in this house is covered in really sloppily-done textures, some of the ridges and lumps are as much as 5 mm high. The roller I've got is useless on it, you can go over the same spot 10 times and still not cover it all.
Can someone give me some advice?
I'm looking at a longer pile roller, but would long (18mm) or extra long (24mm) be better for this?