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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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  • Do you or any of your fellow housemates or guests weigh as much as the TV? If so, do you have any concern walking on your floor? In the US, at least, 3/4" plywood over 16" OC joists are the standard flooring material. If you happen to step dead center between 2 joists, there is no other structural material holding you up when all of your weight is on one foot. That's with the plywood/OSB horizontal on the floor, it's even stronger when it's in a vertical plane.
    – FreeMan
    Jul 5, 2022 at 13:25
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    @FreeMan That's a false comparison. Plywood over drywall vertically into studs while being pulled from some middle position is nothing like pushing some middle position on plywood on joists horizontally on the floor.
    – user19565
    Jul 5, 2022 at 20:06
  • The TV mount I purchased is full motion and not double braced so it's going to hang an 85" TV crooked no matter what. It doesn't seem to be a sorting term so you have to look at the pic before you order. - (As a drummer, I never broke a DB cymbal stand, even the off-brand ones. The crappy ones that aren't can fold up and fall over by themselves. It doesn't automatically mean it's pro-audio gear, but it's deff not if it isn't.) Model number of the mount you purchased?
    – Mazura
    Jul 6, 2022 at 10:07
  • 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.
    – David C. Rankin
    Jul 6, 2022 at 18:48
  • The lag-bolts into the studs will be concerned about the exact same load plus the weight of the plywood. There are strength charts per-lag-bolt as well, but so long as you are sinking the lag-bolts 2" into the studs using 5/16" or 3/8" diameter lag-bolts, you could basically hang small-block Chevy from the plywood. I'd probably use 1x2 strips on the back of the plywood where the studs are to give space for the bolt-heads behind the plywood, Mount the TV mount to the plywood, nail the plywood up and add your 4 lag-bolts 6-12" outside the TV mount and then hang the TV on the mount - done.
    – David C. Rankin
    Jul 6, 2022 at 18:56

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
    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
    Jul 6, 2022 at 9:48
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    A $4k tv had better hover magically above the ground but ya.
    – jay613
    Jul 6, 2022 at 13:35
  • 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
    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
    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
    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
    Jul 6, 2022 at 17:57

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