Previously, we laid out where the retainer walls will be and squared up the corners. Now we’re ready to start digging for the ground-level timbers.
But first: how will we fasten things in place?
I’m using two types of fasteners. One is 1/2” rebar that I cut into 12-inch lengths. I bevel one end a bit, just to help it pass through the hole in the timber (drilled with a 1/2” spade bit) without snagging on the wood. Unless your ground is hard as rock there is no need to grind the pin to a point. Use these pins to fasten the timber in place on the ground.
For timber-to-timber fastening, I’m using HeadLok timber framing screws. You can use a variety of fasteners, from spikes to lag bolts to deck screws. I researched them all. I’ve used decking screws before and found that they are a bit light-weight for this use. And expensive. I’ve used lag bolts and found they hold forever, but the heads have to be counter-bored into the timbers as well as drilling a pilot hole. Extra work, and the bolts are expensive. Timber spikes are the cheapest, but the timbers will jump around as you drive the spikes in, ruining your careful placement to get a good, plumb wall.
I went with the timber framing screws and am happy I did. The cost is more than spikes, but less than lag bolts (in large boxes), and they are rated to replace a 3/8” lag bolt. They are heavy enough to hold well and coated to resist rust for a long time (manufacturer claims “lifetime of the project”). There are several brands out there, this one is what our local home improvement store carries. My 20-volt cordless drill will drive a dozen or so screws before the charge wears down. A corded drill will run all day if I string a power cord out there.
Starting at the lowest corner, I use a square-nose spade to cut the sod along the inner edge of the orange paint line. I cut another line 5 inches inside of that, then dig out the sod between the cuts. These sod-chunks get moved as plugs to the area where I’ve removed and filled in the small, raised bed boxes.
Then I use a pick axe to cut the trench deeper as the ground slopes up.
I use a 4-foot spirit level to check my progress and to keep the trench flat and level until the depth is equal to the height of a landscape timber. Measure the length of timber you need, cut it, and lay it in the trench.
I’m using 6 mil black plastic as a liner inside the wall. My theory is that this will help keep the pressure treatment in the lumber from leeching into the soil and will extend the life of the timbers. By putting the plastic in the trench so it is under the timbers — and up the outside to just above ground level — as well as lining the inside, it should help keep the enzymes (and insects) in the soil from rotting the wood. The pressure treatment will protect the wood for a time. I’m hoping that by lining the walls, this construct will last what is left of my lifetime — or, at least, what is left of it that I will be able to actively garden.
With the liner positioned and a hole bored through the timber about three inches back from the end, check one last time to be sure the timber is level end-to-end and side-to-side, and check that it’s sitting with its edge along the edge of the orange lay-out paint. Then use a small sledgehammer to drive the pin through the timber and into the ground.
The very first timbers (one each direction from the corner) will get pinned at both ends. From then on (at least on this job), only the far end will get pinned; the other will get screwed to the top of the previous timber as they stair-step their way up the slope.
Join me again next time and we’ll get more into arranging the timbers and joining them.