Are crown molding corner blocks a good idea

Crown moldings, or any corner trims really should be nailed to a stud, not simply into unbacked drywall. Without good support, the molding will warp out from the wall causing gaps in coverage to open along the edges.

With real crown, there is a hollow gap behind the molding as only the top and bottom edge touch the wall. The wider the molding, typically the deeper the void behind them. This gap results in having to use longer nails to reach the wall and support wood behind the sheetrock.

One method that works well to make installing the molding easier is to first install a backer/nailer to the wall. Depending on the size of the hollow behind your crown, cut or rip some scrap board, plywood or even strapping, then nail it along the top edge of the wall against the ceiling. You can shoot as many nails as you want to assure the backer if firmly attached to the studs or wall plates, as it will never show anyway. Now, when you go to nail your crown up, there will always be a solid wood backer anywhere you shoot a nail. You can also use shorter nails, or at least not have to use extra long ones. This method is also helpful when your walls are not perfectly flat and an extra nail is necessary to draw the molding in tighter to the wall in irregular areas. Good Luck

What is important when nailing crown molding is hitting a solid background. This can be plates for small crowns or studs. What I prefer to do is add a profile (triangle) piece of scrap wood, such as mitered plywood or ripped 2X4 stock into the corner and nail it into the plates and studs. No problem if you miss or have to use a lot of nails to find a good solid backer because it will be covered by the crown. Now when you go to nail the crown, you will have a good nailer everywhere. I usually use nails along the top edge down 1/2 inch from edge and same along the bottom edge. This helps close any gaps along the ceiling and wall. You can go back after and fill any gaps with painters caulk and touch up to match the crown (if painted) or the wall/ceiling colors respectively.