Electrical – Re-mounting electrical switch box between studs after removing plaster and lath

A swiveling or articulating TV mount will tend to want to pull itself out of the wall when swiveled or extended, more than a flush-mount bracket would. Therefore, this situation calls for a bit of over-building to ensure safety, and to put up with the additional stresses of moving the bracket around.

You will need the following:

• A sheet of 3/4 inch plywood, cut as wide as the gap between the studs, plus at least 3.5 inches. It should be at least 50% taller than the mounting bracket. Hardware stores sell cut pieces of plywood that are 2 foot by 4 foot, so this is an easy choice as it requires only one cut if you don't mine the plywood being a bit over-sized.
• 6 qty of 3.5 or 4 inch lag bolts, or a box of 4 inch deck screws.
• 6 or more 1 inch bolts as fat as possible that fit through the mounting slots on the bracket, plus matching t-nuts and washers.

I suggest you pre-paint the plywood to match the wall or the bracket. Either will minimize the appearance of the plywood.

Center the bracket on the plywood and mark the holes. Drill holes big enough for the t-nuts and install them on the back side. Hang the plywood on the wall and mount it with the lag bolts or the deck screws. If you are using lag bolts, make sure to pre-drill the studs before installing the lag bolts. Since I can install a screw with one hand, I often use 2 deck screws to initially hang the plywood on the wall, then drill and install the lag bolts.

If you use only deck screws, try to find ones marked with a shear force rating and over build by a factor of 2-4. Or just install at least 6 or more per stud to be safe.

The 1/16" difference is not a problem. You are allowed up to 1/4" difference. The slight recess is much preferable to the box edge standing proud. Since nothing ever lines up precisely at this level of construction, better to err a little low than a little high.

The flange thickness is also not a problem. It will push the wallboard outwards a bit, but the resulting bulge will occur over a substantial distance, so it will not be discernible to the naked eye. It's similar to the slight bulge when the ends of wallboards are butted on ceilings and then taped over. There is an obvious bulge if you place a straight edge on it. But once everything is finished, an unaided eye cannot see it except with unusually oblique lighting.

These sort of boxes are a great solution to tight installations.