I have a shelf I want to hang up for my son to put up his gaming console and other expensive items. The studs in my wall don't line up with the shelves mounts. I have some drywall anchors left over from hanging pictures that are rated for 79 lbs in 1/2 inch thick drywall and the mounts require 4 screws, two sets of vertically in line. Can I safely mount the shelf with one side in studs and the other with the drywall anchors if I put the heavier items on the side in the stud? The overall weight of the shelf and all items going on it should weigh less than 79 lbs. The shelf is just over 45 inches long if this is relevant.
No those anchors will NOT be sufficient to hold up THAT shelf. Those shelf brackets are too short and there will be a LARGE pulling force on the upper screw.
Assuming from the image that's a 10 inch shelf and the screws at 2 inches apart, hanging 79lbs on the edge of the shelf will get you a whopping
395 LBS of pull force on the top screw.
When you look at that picture and look at the metal end, does it remind you of any tool that is sitting on top of your toolbox? A claw-hammer perhaps?
You may get away with the type of anchor that mushrooms out behind the wall as shown below. Remembering to buy the size that matches your drywall thickness. But I do NOT recommend these either for that shelf.
With the shortness of that bracket, I'd still be concerned that was not enough to hold up much weight. If those fail, it is going to pull down a rather large piece of drywall too.
Personally I would be inclined to add a backer board out of a nice piece of wood, the wider the better, using one of the following two methods.
Option 1: Outboard screws... Board cut to fit to next stud width. In your case 3 (Don't forget to add a 2x4 width.). Mount board to studs then centre shelf on the wood.
Option 2.: Inboard Screws. Cut board to about 1 inch wider than the shelf. Then centre the board on the studs as shown in the image below.
Which method is best?
Use the method that gets the screws in the wood closest to the screws in the brackets. However, be aware that with the "inboard screws" method, the end of the board will tend to pull away from the wall if the screws are too far away from the brackets.
If the boards spans more than two studs, I'd add another couple of screws at each stud.
If you, or the Mrs, don't like the visible screws, use one of the many capping or plugging methods.
Instead of using drywall anchors, another option is to cut open the wall and add framing with 2x dimensional lumber to place studs exactly where you need them.
For this you require the following materials:
- Stud locator (or you knuckles)
- Drywall saw
- 2x4 or 2x6 lumber, the same as the stud sizes.
- Framing nails
- Drywall tape and mud
- Drywall screws
- Trowel or drywall knife
- Framing screws or lagbolts
- Measuring tape
- Matching wall paint
- A beer
Here's what you do:
- Figure out where on your wall you'd like to place the shelf. Locate the closest studs that fall outside the edge of the shelf. Mark an area around the shelf that includes the studs that you will cut out from the drywall
- Cut the drywall where you marked. Be careful that you do not cut: studs, plumbing, electric, anything else hidden back there.
- Cut the lumber to length so that it runs perpendicular to the studs and runs along where the screw holes in the shelf will go. Judging by your picture you may need to run two pieces lengthwise to catch the top and bottom holes.
- Nail the lumber to the studs. You will need to toenail or if you cut the wall past the studs you can nail through the studs. Make sure everything is level!
- Cut a piece of drywall that fits in the hole. Screw it in place using the studs and your new bracing, but of course make sure not to place drywall screws where the screw holes in the shelf will land
- Tape and mud the drywall patch following the instructions on the mud
- Paint the wall to match
- Screw your shelf into the studs using lag bolts