So, as it snowed lightly today, I thought I would give the sonotube footings a try. (It was snowing, but the temp was hovering around 40) I cut them about two inches, because I didn't want the lower ones on the slope to stick up too much. If this were a real deck, I would want them to rise about 8 inches or more above the ground-line, but in this case, I have a limited scale (I can't go higher than the roof of the playhouse), and there will be minimal human use. I don't anticipate a drainage problem. I may put pea-gravel all around underneath to help with this. Anyway, I put the tubes back in, checked them for level and plumb, and then mixed the Quickcrete (portland cement, add water).
Then, after mixing 80 pounds (enough for one 22 inch sonotube) with 3/4 gallons of water, I put the concrete in the tube. What you want to do is perform a quick slump test, to see if the 'crete is right. You put some in a bucket, and turn it over like a sandcastle. If it slumps a little, but doesn't lose all shape, it is the right consistency. Here I am in the middle of mixing and pouring:
Then I inserted the threaded rod, which is about 12 inches long with a curved end at the bottom, and the threaded bit at the top, in the center of the filled sonotube. I wanted to leave 4.5 inches above the concrete, so that I could use at least 3 inches of lumber as blocking (two 2x4s), or even three layers of blocking with a countersunk hole. Here I am, measuring the rod:
Then, I repeated this process three more times. The hardest bits were physically carrying and mixing the concrete, and keeping the tubes plumb and level. I also noticed that sometimes I had extra in an 80 pound bag, and sometimes was a couple inches short, which is odd since I cut the tubes exactly the same height. But there may have been some seepage at the edges of the paver, or I just lost some as I was dumping it in. Who knows? Anyway, I got them all in, here they are:
Finally, because I didn't know what the weather would be like tonight, and because it's common practice with slabs, I put plastic over the finished tubes, and weighted the plastic with rocks. It takes 24 hours to cure enough to build on, and it takes about 7 days to cure completely. Next stop: deck framing!