It wasn't "unfollowable", it was more I didn't see the choice you suggested in the menu -- actually it was grayed out. It was these steps:
"-now put a layer mask on your “damage” layer and hide the whole thing.
-Select the layer mask for your damage layer
-make your selected color white
-Using your funky brush you can now draw in additional damage wherever you messed up the walls extra. its like magic or something!
-finally to help define the edges of the broken stone we’ll add a layer effect like so:
"
When I was on my damage layer, there was no option that flat out said "Add Layer Mask" -- my choices were Reveal All, Hide All, etc. I chose Hide All and it created a filled black layer mask, but when using my funky brush, it seemed to just draw a shadow under the walls rather than damage on the walls. Or maybe I just drew on the wrong layer or some other newbie mistake. I thought it looked OK without that extra step in this case, though, so I deleted the mask and went to the next step.

Now I want to try to adapt this to creating a beach scene since one of the games I am running by post has the players trapped on a deserted tropical island. I'm thinking a sand instead of dirt layer and a longer grass texture for the grass layer, and a more tropical looking tree texture for trees.