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djgrant 10-04-2011 03:03 AM

Mounting huge TV+sound bar above TV with down&out mount
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I'm about to mount a large TV + soundbar above a fireplace and I'd like to hear some thoughts about my plan before I go ahead with it.

I've attached a picture that roughly shows the location of some studs as well as the location of where I plan to attach the mount to the wall. Note that this is the "down & out" mount which swings away from the wall, allowing the TV to come down to eye level. The two large green rectangles in the picture roughly show the position of the TV in the high and lowered positions.

  • Shear load: Should I be worried about 95 lbs of shear on the wall or studs at all?
  • Tensile load: I plan on screwing the four 3/8" x 3" lags that came with the mount into the studs. Because the studs are quite a bit off-centered versus the TV, the left-most top lag will be taking most of the tensile load due to the torque of the TV. I talked to the mount manufacturer and he said that the top bolt or bolts will take about 300 lbs of pull-out force for a 100 lb TV (I assume this is only if the TV is in the pulled-out position, and it will normally be in the down or up position).
  • I'm using 2 different stud finders so that I can make sure to hit the center of the studs. One is an edge finder and the other is a center finder. I figure that getting the center of the stud will be pretty important?
  • Pilot hole size for 3/8" lags. I tested some pilot holes on a 2"x4" and the suggested 1/4" pilot hole didn't seem that tight to me. I tried going all the way down to 1/8" pilot hole and I still didn't cause the 2"x4" to split, even with a hole drilled near the edge of the stud. This stud perhaps a bit softer than what is in my 30 year old walls, however. Anyways, I may use a 15/64" or 7/32" pilot hole just to get a bit more holding power there. Does anyone have any experience with pilot holes for 3/8" stud and what they recommend?
  • I was going to use 4 SnapToggles as well, will these actually do anything?
  • I didn't see the point of putting some plywood or 2x2 backing or anything. I can't see how that will make any difference. Anyone disagree? In the end, all the forces will still transfer to the studs or the drywall. Hopefully they will help spread the load a bit?
This is the first time I have ever mounted a TV, that's why I'm being extra careful. I have done a bit of DIY stuff around the house but I've never hung anything heavy from a ceiling or hung anything ridiculously heavy from the wall. I'm hesitant about having an installer do this as I doubt they are aware of this mount and will not read the instructions for it as carefully as I have. I also don't trust them to take the time to do it right.

Ron6519 10-04-2011 07:13 AM

Open the wall and install additional framing to deal with the weight.

rjniles 10-04-2011 07:18 AM

Another concern is how heat from the fireplace will affect the TV.

Open the drywall and install blocking. Then re-drywall.

josall 10-04-2011 07:38 AM

I thought everyone answered your questions in your 9-19 post. If you are still worried open the wall and add blocking as suggested above. Stop worrying about it and screw the thing up already.

Mr Chips 10-04-2011 07:58 AM

15/64 is the correct size pilot for a 3/8" lag (1/4" in hardwood). I ususally use a 3/16 because they seem to be easier to find in the garage when i need one. Don't go crazy trying to use smaller ones, there is no advantange.

The strap toggles can't hurt and might offer some protection in the event that a lag bolt fails. They are cheap enough and even if they don't help, i can't see any harm in using them

If it were me I'd rethink the mount you are planning to use and switch to a staionary one that will tilt downward slightly. I find this set up much more comfortable to watch, and without creating all the extra leverage and potential wear on the moving parts. Have you tested the viewing heights to see if you would actually utilize the drop down mount? If not i would recommend setting the tv up on top of something at the low height for a week, then using a tilt mount and watch the TV mounted at the higher height and see what you like better. the higher height is more forgiving of different room sizes and furniture arrangements

moneymgmt 10-04-2011 08:10 AM

Your questions have been answered many times over, between this thread and your last one which was identical. If nobody has read the instructions as closely as you why don't you just do what they instruct! If it fails that way you can go after the manufacturer. Keep screwing around with drilling through studs and toggle bolts and all this other junk and you have no way of knowing if it will work, and if it fails, no one to blame but yourself. I'm sure the manufacturer has sold a few of these mounts and tested them per their own instructions; your fireplace is not unique.

djgrant 10-05-2011 01:55 AM

@josall @moneymgmt: Sorry I do not agree.

Many of my questions are unanswered. For example: 1) my last question about installing blocking/backing or whatever you want to call it; 2) my question about shear load, based on the studs I've drawn and the assumption that there are probably some floor-to-ceiling studs there as well to the left and right; 3) my question about importance of hitting the center of the stud. Not a big deal, I'm just going to try to get the center as best I can, but since I've never attached anything major to a stud before, was looking for some real world experience on how important this is (eg. anyone ever caused splitting in a stud by missing the center?); 4) my question about using SnapToggles where indicated in there any point?

I don't think those have been answered, correct me if I am wrong. I'm curious, that's all. I like to know and learn things and ask questions.

@moneymgmt: good point about following what the manufacturer of the mount says rather than deviating from that too much, although I don't think I can "go after the manufacturer" if the something happens to the wall/studs or anything besides the mount itself. I prefer to use as much of a margin of safety as possible, and if I can make the mount more secure without compromising something, I will.

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