4. Alternatives. The sponge is common, I tried some steel wool, but it wasn't coarse enough to make any difference, but I used it for a tiny bit of a smoother finish. However, half way through my job, I found this sitting in the garage:

It is a kind of rough foam sanding block, it was perfect. It was a bit rougher, so it gave a better finish. But don't worry if you can't find it, the sponge does a great job, and is of a good roughness.