So, the test projects for the concrete work were sucessfull. I still need to get a grinder and grind/polish/seal the test bits to make sure they will finish up the way I want them, but it works. I now am comfortable with the process, and ready for more. This means it’s time to start thinking seriously about the big project I want to do, the desk top. This was inspired by a polished concrete computer desk project I saw on Instructables awhile ago.

As I’ve posted in the past, I built my current computer desk. It’s made from a pair of rectangular structures that house computers, with a desk top stretched across the top. There is also a pair of thin, tall shelves that rest on the top of the desk. By design, the entire setup is modular – each rectangular section that hold a computer is totally separate from the desk top, and the shelves just rest on the top of the desk. My plan is to replace the desk top itself with a concrete slab. This is going to happen when I move the office into the shed, after the shed is refinished with insulation, better power, and an air conditioner. Due to size and weight limits in the shed, I’m currently planning on making the concrete slab 8’x3.5’x3″.

One of the first major considerations is that a slab of concrete that is 8’x3.5’x3″ will need significant internal reinforcements. Likely rebar, which was designed specifically for this kind of work. Rebar is cheap, easily workable (if you get the thinner stuff), and has roughly the same thermal expansion coefficient as cast concrete, so it’s less likely to crack over the long term. There is also epoxy-coated rebar available, which helps to cut down on corrosion issues internal to the finished product. I’m not sure the slab will be under conditions where this could be a problem, but it’s something to think about. There’s also the idea of mixing reinforcing fibers into the concrete mix as I go – there’s a spun basalt fiber that I’d like to try – but that is going to add cost and complexity to the project. I think I’m going to go simple and old school and just stay with the rebar.

The next question is “how strong are the end sections of the desk”? Well, they are strong enough for me to stand on, which is good, even at my heaviest weight (252 lbs this spring). Considering that the slab will be 600-800 lbs or more, this is good, but I may need to redesign some of that, or add addiitonal supports. Part of me is tempted to get some 4″x4″ wooden posts and use them as table legs. We’ll see.

Finally, there’s the question of cable runs etc – do I want to punch holes in the slab to route stuff through? I can’t do it later and be practical, as I won’t be able to move the desk once it’s in place, and I don’t want un-needed holes. I do know I want some in place. The PowerMac Cube comes to mind in that case. I also want to consider adding mounting hardware to allow me to attach monitor arms to suspent the iMac and a possible Cinema Display or TV down the line, so those supports will have to attach to the back of the desk, and be anchored will in the slab itself. There is also the possibility of simply running thin holes directly through the back of the desk, to run the threaded support rod from the mounting hardware through the desk.

Really, I want to do this project, and not get too wound up in making it overly complicated. I’ve finally gotten the mix and wetness down properly, and I can consistently pour a decent slab without too many bubbles – so this could all work. The one thing I’ve not tried – a coloring agent – doesn’t seem very difficult from what I read online, so that’s not an issue either. The biggest thing now is to find the time to actually do this. Then comes the logistics work of renting the cement mixer, buying half a ton of cement, and getting it all to the house. It’s going to be a serious workout lugging the bags, mixing, pouring, etc, but that’s not the end of the world.