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Most of the answered related questions seem to be for smaller sized TVs. So here's a similar question with slightly different condition.

I have a 85 inch TV I want to mount on the wall, so it will be 100+ lbs.

The TV mount I purchased is full motion but my studs does not align with it nicely. So the TV will be off center if I place the TV mount on the studs where they currently sit.

So my plan is to get 3/4" plywood and bolt it to the TV mount with nut and washer. Then use lag screw to attach it the plywood to the 3 studs in the wall.

The other option is to use lag screw two horizontal 2x4 into the three studs then attach the TV mount to the 2x4s.

My question is will the plywood option have enough hold for a 85" TV with full motion TV mount? Also will 2x4 in this case be stronger?

A more general curiosity is the strength TV mount on 3/4" plywood with bolt + nut vs 2x4 with lag screw?

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    What you are concerned about in the mounting of the TV to the plywood with bolts and washers is the Sheer Through Thickness, see Plywood Design Specs (pp 2) which for normal 5-ply 3/4 in. on 16" centers is 93 lb/in or more. This would be roughly per-bolt. The per-bolt weight carrying (Planar Sheer) is multiple times as strong. The Sheer Through Thickness for the TV is only due to the bending moment (TV weight x dist from plywood) which will be a fraction of TV weight if less than 1 foot from plywood. 3-4 bolts are fine. Commented Jul 6, 2022 at 18:48

2 Answers 2

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There are "three stud" TV mounts where the backing plate is wide enough that you can connect with at least two studs and then mount the TV exactly where you want, even if it isn't centered on the backing plate.

If you have properly constructed wood studs, four well-mounted screws in two studs is plenty. Don't make it more complicated.

For a full motion mount with a big TV, my suggestion as to where you invest time and effort is buying high quality lag screws, making sure you are dead center on the studs where you mount them, and predrilling so you get full strength without splitting the wood or breaking the bolts. Know how thick the drywall/plaster/whatever is. Know how far into the stud your screws will penetrate. Know exactly what's behind the wall. That's what will make or break a full motion installation. Start with a suitable TV bracket (ie a wide one) that can hit two studs, without extra layers of wood, and with your TV exactly where you want it.

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    On my initial research most of the mounts that are "wide" doesn't really swivel left and right (which is what I want), but I probably did not spend enough time looking. You are right, maybe I should just get a different mount, I guess I was trying to avoid it in back of my mind due to shipping + restocking fees.
    – Allan Suen
    Commented Jul 6, 2022 at 0:16
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    'TV mount I purchased is full motion but my studs don't align with it nicely.' any mount that you should use for an 85" TV will be over x2 studs somewhere (doesn't matter where) at 16"c. Otherwise it's not a mount for an 85" TV. Get double braced. My advice is to buy a $300 mount for a $4k TV.... w/e lags it comes with will be fine.
    – Mazura
    Commented Jul 6, 2022 at 9:48
  • It bears repeating: well-mounted, properly sized, high-quality screws.... I've gotten some pretty cheap lag screws (poorly manufactured of weak metal alloy) included with mounts that I've sheared off with little effort. I bought some good screws from my local hardware store to replace them and had no problem. I wouldn't trust my high-end TV to inferior mounting parts.
    – Suncat2000
    Commented Jul 6, 2022 at 18:13
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Yes.

3/4" plywood is very strong, and if you use a sheet of sufficient size will provide very good support. Assuming 16" stud centers I suggest about 52"w by 16"h. This will give good lap over the side studs and enough height to provide rigidity. Add length as needed for positioning or for wider stud gaps. Mounted with three 3" screws on each stud you can hold far more than your TV requires.

You can actually use lag screws into the plywood*. No need to futz with bolts and nuts. Positioning can be a real pain with that approach. Just be sure to pilot properly (slightly smaller than screw shank diameter) and don't overtighten. Screws should be 5/16" or larger. 3/8" is probably ideal, assuming your mount can accommodate.

* You haven't specified what "full motion" is, but I'm assuming a reasonable extension and not a three foot articulating arm. (I wouldn't want to move an 85" TV around like that anyway.)

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  • Thanks. By full motion I actually just want a TV mount that can swivel left and right, but it seems like most mounts don't support that on a big TV without having an arm that extends far out.
    – Allan Suen
    Commented Jul 6, 2022 at 0:10
  • @AllanSuen - "With 2 double supporting arms and 3 articulations swiveling up to 120 °." $378.99 google.com/shopping/product/… "but I probably did not spend enough time looking" - nor thought for a second that I'd be spending a third of the money on a mount.
    – Mazura
    Commented Jul 6, 2022 at 10:19
  • full motion is just a vague marketing term that means the mount can adjust the display in two or more directions and/or angles. The technical specifications for the mount usually state the maximum range limits of those directions or angles of movement.
    – Suncat2000
    Commented Jul 6, 2022 at 17:57

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