A Boring Retaining Wall Pour


Moon High over Forms and Foliage

Something is wrong with this picture. What I am showing here is how the forms come together for our retaining wall pour. The wall curves around what used to be the atrium in our old farm house. The forms are 4′ wide by 4′ high right there but on the outside of the curve they must be longer so we had to shim the outside of the curve with 2×4’s to make those forms just a little longer. Then we used LedgerLock screws to join the forms to each other. The forms are held to the opposing form on the other side of the pour by 5/8″ threaded steel rods 32″ on center that penetrate 2×6 brace boards on either side of the form work.

The header boards at the top also hold the forms together as well as making it easier to get the concrete in the narrow wall. This was a 3″ thick by 4′ tall retaining wall. That’s very thin. There is lots of 661010 Welded Wire Mesh (WWM) in it as well as #4 (1/2″) rebar along the top and bottom and it has steel pins connecting it to the old wall. In fact, I used up a lot of my scrap WWM in this wall. With that and its curve I am sure it is secure. When finished the wall will also be buttressed by the next wall east.

The purpose of this wall is to protect the insulation of the building from my plowing, from the chickens pecking (they love pink insulation) and to make sure water running down the mountain doesn’t come into the building. The driveway is landscaped with a slope to keep water away but this represents one more level of protection.


Holly Testing Scaffold

Back on the greenhouse project we had used forms wire to hold the forms together which is the standard technique in the concrete industry but I really didn’t like it. The wire is not sufficiently strong and you have to do a lot of wires to get safe forms. There are other pass through devices that I’ve used in the past, in fact right there on the atrium wall 20 years ago, but they lack the one big advantage of the threaded rods mentioned above: They are a place to hang our hang scaffold.


Ben on Low Scaffold

The threaded rods are strong enough that we can simply place 2×8 planks on the rods to get instant scaffolds. With the addition of some supporting legs they feel rock solid. As we move ever upward this is important. Later we’ll be pouring at 8′, 12′ and finally 20′ for the tower of this building. Secure scaffolding, stable forms and places to clip in while working are important. My decades of rock climbing experience will prove useful…

Another advantage of the threaded rod is I can later use it to tie my outer rock wall when I do a folly tower. We’ll do the inner wall, insulation and then an outer wall. The threaded rod has a small surface area for conducting the cold through the insulation but it will lock the essentially two separate concentric towers together. Another project for another year but I’m working out the techniques now. For this project it will help us super insulate by giving more tie points on the outside for insulation. On the inside the insulation will be under compression so it won’t need the extra supports.


Finished Retaining Wall Poured Looking North

I said this was a boring pour. I like that in a concrete job. Boring is good. Uneventful. Nobody died (I did break three ribs*) and a small amount of concrete tried to escape one hole at the north end but other than that it was a very boring and quick pour. We also had exactly the right amount of concrete which is always nice.

We had a front dump concrete truck again for this pour. I had ordered that since he is able to control where the concrete goes so well. From his cab he can swing, raise and lower the chute to reach all of our wall. This saved a lot of time and hard work. The result is the project went faster, we wasted less concrete and were not as tired at the end of the day. The cost? $20 for the front vs back chute. The one catch is the front chute truck is a lot longer and heavier. He inches around our driveway’s first corner, scooting back and forth a few time

We also used small 3/8″ stone and a high slump of seven on this pour due to the thin walls filled with so much steel. The result was the concrete flowed very smoothly, quickly filling the forms with a minimum of paddling by us.


Finished Retaining Wall Poured Looking South

After we got done with the pour we bevelled the top of the wall so that water will dump to the outside edge. This is the first time we have gotten to do finish work on the Big Project. All the rest of the concrete has been sub slab stuff. Exciting! Usually we go ahead and do the finishing for practice and then have to rough it up before the concrete sets so that the next pour can properly bond to it. Holly says she’s always disappointed to see the smooth slab get scarred up. But it is worth the practice to be able to do it on areas that don’t matter.

As shown in the photo above we have de-formed, that is to say stripped, the super insulated slab for our, er, ice cream shop[1, 2] and started to move our construction materials and form building up onto the slab. All that nice level open space can’t be let to waste! It also means that as forms are made they are right there where we need them.

On the top of the forms you can see we’ve put insulation. This is to protect the concrete from the cold. We also poured with 1% Polarset to help deal with the cold. In retrospect I would have gone with more but the 1% did well.


Finished Retaining Wall Peel

After three days I couldn’t resist peeling one little section. This is a buttress point which just had plywood so it was easy to get at. The concrete is still below a 2.5 Mohs Hardness but it is coming along. The concrete looks great, very smooth and uniform, but is still very green due to the low temperatures. I’ll leave the forms on a little longer while we work on other parts of our project. After peaking I put the plywood back on to protect the nice smooth finish.

So what is wrong with the top photo? Care to guess? The answer is here but don’t peek until you guess. For the adventurous, leave your guess in comments…

*I tripped on a brace stake, spun and landed on another – very gracefully I’m sure. Ribs heal and there’s nothing to do for them but breath gently and not laugh too hard.

Outdoors: 40째F/26째F Sunny
Tiny Cottage: 53째F/48째F