My task was to attach a 42" Flat Panel LCD Monitor using an articulating arm mount on a 3" thick wall supported by aluminium studs My method would be to replace a piece of drywall with a piece of plywood that spans three aluminium studs. I would then use toggle bolts to attach the mount to the plywood. I finished it off using layers of drywall compound, sanding, and painting.
The Wall
As seen from the above picture, the wall is 3" thick. There is 0.5" of drywall on either side of the wall, meaning the studs supporting the wall are 2" thick. The studs themselves are simply aluminium drywall support studs and are not solid. The studs are 16" apart. I tried my best to find out all this information before ripping off the drywall by asking my condo's superintendent.
The TV
The TV to be mounted is a [url='http://www.westinghousedigital.com/details.aspx?itemnum=44#VALUE']Westinghouse LVM-42w2[/url]. It is a 42" 52lb. Flat Panel LCD.
The Mount
The mount used is the 8.40lb. 20" articulating arm LCD mount, [url='http://www.peerlessindustries.com/Products/BrowseProduct.aspx?modelID=156865&productID=149296']Peerless Industries SA740P in black.[/url]
The Steps
1. I first identified the location of the studs. I accomplished this using a Zircon SL Electronic Stud Finder. From this, I determined that the studs were 16" apart and marked their locations on the wall with a pencil. I'm not sure if it was the sensor I was using, or the fact that these studs were aluminium, but the studfinder indicated that these studs were about 2" thick - In actuality, they were just over 1" thick.
2. Then penciled the dimensions of the required plywood. I decided that I needed to distribute the weight across three studs, which means the length should be 48". I also decided that approximately 20" in height would be required.
3. I then went to Home Depot and asked them to cut me a piece of thick birch plywood (1/2" thick) to the dimensions of 48" x 20". They would not cut me a small square in the middle for wires. Unfortunately, Home Depot screwed up the cut because it was not a perfect rectangle. Insist that the plywood is perfectly rectangular!
4. I then started cutting out the drywall I was anxious and did not want to wait another day to buy a jigsaw to help with this process... So, I used a utility knife. Ugh - long, difficult process. Fortunately, I had some help.
.
5. I placed the custom-cut piece of plywood into the cutout. The cut-out was about 0.2" wider than the plywood, to ensure a perfect fit. You can't see it in the photo, but along the bottom-left and the top-right of the plywood, there is a larger space than there should be, and it did not rest on the metal studs appropriately.
.
6. I then used 11 drywall metal screws to attach the plywood to the aluminium studs. 3 on the first stud, 5 in the middle, and 3 on the end stud. (insert picture) I would have used 5 on each, but as I mentioned, the plywood was not cut in a perfect rectangle, so it did not rest completely on the end studs.
.
7. I slathered on the drywall compound. This is where I had to really learn how to do a proper job. The proper way to do this is to apply a very very thin layer of the drywall compound using the largest putty knife you can find. There should be very few ridges and very little need for sanding if applied properly. Then, let it dry, sand it, and apply another layer - extending past the edge slightly more. Dry, sand, and re-apply - eventually, you should be tapering off the compound about 6" from the actual edge.
I, again, was anxious, and just attemped to slop on as much as I could. It's not supposed to look like this. I placed drywall tape along the edges of where the plywood met the drywall. I then placed putty all over the plywood to give a similar texture as the wall.
.
8. I sanded using an automatic sander using coarse sandpaper... and painted. I wasn't happy... and my condo was filty with drywall dust! So, I re-did the putty... this time, the proper way. I used three layers of putty, and it barely required any sanding.
This time, it looked decent.
9. I then used 2.5" long 1/4" toggle bolts to attach the mount to the plywood. I did not use the bolts that came with the mount since those are meant to be used in a solid 2"x4" wood stud... not a 1/2" thick piece of plywood...
If you want pictures of the bolts I used, I can post them, but these were the standard ones.