07-08-2016, 05:08 PM
I have built concrete corner posts for my fence using 12" x 12" x 8" column blocks, 6 blocks tall. I started by drilling 1 1/2" holes into the rock as deep as I could go which was about 18" deep. These holes were located at the inside corners of the concrete blocks. I used anchoring cement to grout 1/2" rebar into the lava. The anchoring cement is available in small tubs at Home Depot. You have to mix it really runny so it will flow into the hole around the rebar and you have to be fast because the stuff begins to set up in a couple of minutes.
You need a large rotary hammer and a 1 1/2" bit of sufficient length. You also need a large solid chunk of lava where you need to put the post. If you do everything right, and with a bit of luck, your finished posts are cemented into hundreds or thousands of pounds of solid pahoehoe and aren't going anywhere. So far my posts are keeping my fence drum tight. They are probably holding hundreds of pounds of tension, cantilevered directly out of the ground without diagonal braces, and the installation required only cleaning away the surface dirt down to the underlying lava, then drilling.
You need a large rotary hammer and a 1 1/2" bit of sufficient length. You also need a large solid chunk of lava where you need to put the post. If you do everything right, and with a bit of luck, your finished posts are cemented into hundreds or thousands of pounds of solid pahoehoe and aren't going anywhere. So far my posts are keeping my fence drum tight. They are probably holding hundreds of pounds of tension, cantilevered directly out of the ground without diagonal braces, and the installation required only cleaning away the surface dirt down to the underlying lava, then drilling.