One day I realized that I didn't have enough distractions in my life, so I decided to try to make a keyed papercrete block.

What was I thinking? Well - if it worked out I would have a block that could be stacked without mortar. This would make a structure that could be taken apart and moved from place to place if desired, and erected without mortar.

The first attempt was a complicated mold with small "V" shaped keys, offset on opposite sides so they would match. I filled the mold, let it sit a while until the pc started shrinking away from the mold, and took the mold apart. Oops, way too soon to remove the mold, it collapsed from its own weight.

OK, the next thing I tried was filling the mold, letting it settle some, and topping it off with fresh papercrete. I then let it drain and set for a while until it got firm and I could remove the mold without it slumping.

This block didn't collapse, but in curing it shrank in the middle and on top, giving an odd shaped block that would not be suitable for stacking.

On the third attempt I filled the mold and then topped it off several times, pressing the new pc down each time. I left it in the mold overnight. Still too much slump to be usable, but getting better.

Of course, I was aware that the mix I was using wasn't ideal, low on portland cement and without any sand or dirt. Not really wanting to change my mix, I decided to cut up a pc slab I had sitting around, and put a couple of pieces in the mold, filling it except for a couple of inches on the sides and top & bottom. I surrounded them with wet pc, and left it until the next day. When I removed the mold I had a fairly consistent block, looking like it might stack ok.

At that point I decided that this method was too labor intensive, not simple and one step like I prefer.

With that in mind I abandoned that mold design and traded it to a friend who wanted to use it for concrete. He offered to make another mold for me in exchange. When he delivered my design, a mold that makes three large keyed blocks using about a half load from my mixer, I filled it and left it to sit overnight.

When I removed the mold I had three blocks that stack up pretty well without mortar, though they ended up not exactly squared.

After all this, I realized that I had things with a higher priority, and set the project aside.

I don't know if I'll put any more time into this, I prefer geodesics over boxes, and these blocks aren't very useful for domes.