Dirt Work 2
The first step in digging the foundation trench was to rope off a dig area. The bottom layer of blocks, called the footer, was going to be turned 90 degrees to the rest, so that they gave the foundation a width of 16 inches.
So I knew my trench needed to be at least 16 inches wide. It also needed to be about 3 and 3/4 blocks deep, which is about 30 inches. I measured out a 32x24 area that was 16 inches wide, and I used a bunch of stakes and twine to mark the whole thing. Before long I had dug up most of the twine and some of the stakes, but I knew basically where I was going.
At this point I had already made my first mistake.
The problem was that my garage was not going to be a perfect 32x24, no matter how hard I tried. This was because I was using concrete block for the foundation and there was no way to obtain a perfect 32x24 using 8x8x16 block. So, I ended up needing something like 31'6" by 23'4" or something wierd like that. It was important to be undersized rather than oversize so that my framing would still go together properly. Remember that OSB comes in 4x8 sheets and if my garage had been 32'8", I would have a tiny strip of OSB at the end, which is not good structurally.
So my trench was too big and I would have to correct for that later as I was laying my block.
One bad aspect about laying block for the footer was that the bottom of the trench needed to be as close to perfectly level as possible. I bought a cheap laser level, and I would level it perfectly at one end of the trench and see where the beam ended up on the other end. I would use this to get the bottom as flat as possible. But the real work of getting it perfect would wait until I was actually placing the block. At that point I would place the beam at the precise height of the tops of the block and make sure they were all exact. Well I never was able to get them perfect, but within about 1" from one end to the other seemed to be fine.
In retrospect, it would have been better to have the footer poured instead of using block. It would have meant another trip for the concrete truck, so it would have cost a lot more, but I could have used forms and leveled off the top of the concrete much easier than trying to get the bottom of the trench perfectly flat. Oh well, it only added about a month to the workload, ha!
Digging for the foundation ended up taking a huge amount of time due to the presence of granite. My mini excavator could only do so much. I had an air compressor, so I decided to buy an air chisel to see how well that broke through the granite. It actually did an amazing job of breaking much of the granite into little pieces that could be dug out. but there were some areas that were too solid. For those areas, I rented an electric jackhammer called a Bosch Brute. It ran on normal 15 amp household current with about a 50 foot extension cord. Not as fast as an air powered jack hammer, but easy to use for an amateur.
After a few weeks I finally had a trench that seemed good enough to begin laying block.