The wiki states that
wall-solidification can also be sped up by right clicking a foam block with a block of sand.
I have tried this with both regular sand as well as sandstone.. not sure what else "block of sand" could mean, but neither of those do anything other than place sand/sandstone next to the CF.
If whoever wrote this is intending for the sand to fall into the CF... I don't think any sort of benefit that that brings would have been intended by the devs. If it IS intended to help, then placing sand inside of CF needs to be a little easier to accomplish.
If, however, this portion of the wiki is incorrect.. just say so and I'll go edit it out (if no one has already done so)