Reflections of The Dragonfly Den, June 2009–and Beyond: A Form to be Reckoned With!

8-10 July 2009 – As I mentioned in the previous post, I was using scrap/crap wood to make the top oven slab form. Being basically cheap, I had scrounged pieces of wood to make the form not realizing what a critical part of cement work it is. I cut several pieces of plywood to act as a form bottom for the areas over the bays and the front span. Again, I jammed some scrap wood under the plywood and figured that was all I’d need to support the concrete poured on top. As you can see, the form was better suited to a load of packing peanuts. I was really lucky that the poured concrete did not collapse my rickety form while it was fluid & curing. It was a real heart stopper when I experienced the force that a yard of concrete can exert pushing out when poured into a form...again, I was really, really lucky I didn't end up with a big mound of concrete where my oven stand was supposed to be. I now appreciate when I see someone has installed a strong, braced form for ANY concrete work.

To back up a little, I had decided that I wanted to include an ash chute into the build. I didn’t want to be shoveling out the oven (or hauling ash & coals around) when Susan was setting a dinner table. Being able to pull the ash into a container to be dumped later (after the party) seemed a good idea. I researched and found that if you put a solid block of something into an area to be filled with concrete, it’s called a void form. Once the concrete hardens, the void form is removed and surprise...there is a “hole” in the concrete. I took two pieces of 2x4 the length of my projected oven opening, nailed and glued them together (what an idiot, over-achiever I was on that) and wrapped them in plastic. A couple of screws up through the plywood base piece and the ash slot was ready for the pour.

I used 3/8" rebar on the main slab and ran a couple of ½" rebar pieces paralleling the ash slot void form. I figured since the ash slot would be in the front span, a little extra strength wouldn’t hurt. I also had a couple pieces of angle iron and I simply laid them along the front edge of the span and over the left bay. The rebar was bent 90 degree into alternating holes of the side-wall blocks. These block holes would be filled with concrete, tying the sides into the top slab with not only concrete but rebar. The other holes were simply filled with crumpled newspaper and cardboard to keep out concrete...no need to fill all the holes.

As I mentioned in the FB forum, I attempted to mix all the cement myself for the top oven slab and alternate block holes. Two batches, two bags of ready-mix cement each and I realized that there was no way on earth I would be able to complete this job before things started seizing up.

In retrospect, one of the smartest things I did in this entire project was to call the local ready-mix delivery truck and have them bring me out a yard of concrete. Fortunately there was a truck available and he arrived before noon. I think he was quite amused with the form I’d built, but was really helpful and we got the slab poured. He showed me how to scree and float the slab so it was finished pretty nicely. It was interesting that this man said he remembered our house foundation was one of his first jobs...almost 40 years ago...wow!