Can I mount my TV & wall mount on plasterboard without a stud?
Sounds like real honest to God plaster over expanded diamond lathing or old style wood lathing. 2-3 inches isn't plasterboard (drywall). That's plaster. You should be ok if you installed the anchors correctly and used the correct anchors for the extreme depth of the plaster. Those things can hold up to 200 pounds per anchor. Technically, you should hit studs, but I really wouldn't worry about it if it seems secure. Could it fall off the wall? Yes. What are the chances? Low if you have chosen the correct anchors and installed them to specification. Enjoy your new flat screen!
If the tv is fairly light it should hold ok but the problem with plaster walls is when it breaks up it usually does it in mighty big chunks of it at a time. The older it is the more brittle it becomes. Personally I would have felt better hitting a stud when mounting it but maybe you won't have a problem.
It is probably plaster and it will not hold. You need to locate a stud and attached it to it. Get a stud finder to locate a wall stud. If that is a plaster wall it will break loose in huge chunks and it is neither easy or cheap to repair.
You're okay. Just drill 6-7 holes and rapidly insert wet glue in there, then stick the tv in there
2-3 inches deep? then you should be fine although i would try and spread the weight out as much as possible, the more surface space you use the less tension in one area so use some of those alligator things that go in but not out. use your good judgment on this one if it seems sturdy enough then go for it