My 'mil' wants me to put in some heavy duty shelves like I put up in our home for books/business/work stuff. She has plaster walls. I don't--it was easy to find studs on my panelled walls and easy to secure the vertical brackets to the walls. How do I screw in the brackets to the plaster walls without drilling extra holes that can't do anything? Can you tell I have tried and failed with that in a prior project? They actually crumbled on me once. What kind of fastener can I use? What if I need a support where there isn't a studwall? Thanks.