Sunday, May 8, 2011

Sunny 2.0: The Big Muddy

Last weekend Greg and I rebuilt the foundation for the clay oven and poured a concrete counter-top. We took the forms off on Tuesday evening and for our first concrete counter-top attempt, it turned out really great. On Saturday (yesterday) Greg headed to Menards for some stuff he needed for installing some drainage tile in some low areas in the vineyard. Before he left, he mixed up some coffee colored stain in a spray bottle and sprayed the concrete. It dried pretty quickly and looks great. We may do another layer of stain once Sunny is finished, then we will seal it.

While he was gone, I got started on Sunny. I hosed off the concrete and spent some time leveling the sand bed and installing the fire bricks. I leveled the sand, added a little, and slid the bricks into position, and tamped them down with a hammer so they were flush with the edge of the concrete.

Once done with that, I gathered together all the bags of sand I could find and started building the dome on top of the bricks. The dome will serve as the mold for the oven shell and once the shell is hard enough to support it's own weight, the sand can be pulled out leaving a cavity. I got about half way through building the dome when I realized I might not have enough sand. I stopped, shoveled all of the sand into 5-gallon buckets, and went looking for something to take up some of the space in the dome. After considering several things, including a 5-gallon bucket, I realized that whatever I used needed to be able to fit through the 10-inch tall doorway opening, which would be the only way to remove it. This eliminated the bucket as an option. I eventually settled on four plastic milk containers. I filled them with water and tightened the lids, and arranged them in the center of the circle I'd drawn as the outline of the dome. I then started piling all of the sand back into a dome shape.

Before I built Sunny 1.0 I had read Kiko Denzer's book "Build Your Own Earth Oven" and used it as a guide for my own clay oven. One mistake I made, in spite of the book's indication that it was pretty important, was that I made the door too tall, which caused a lot of heat loss, and took a long time to heat it up to temperature. I had used a slab of quartzite as a sort of lintel and it was unable to withstand the high temperature, and eventually fell apart (well actually it exploded into pink shards).

This time, instead of a horizontal rectangular opening, I'm going to use an arch which will make building a door a bit more complicated but should be a very strong opening.

Back to the sand, once I'd piled up a dome the dimensions of the oven cavity I wanted (17 inches high, 29 inches across) I soaked some newspaper in water and covered the dome with it. This helps to separate the oven shell as it dries, from the sand which will be removed by hand. It makes removing the sand easier, and also prevents sand from clinging to the inside of the shell of the oven, and raining down on your pizza as it cooks. Any bits of paper still clinging to the oven shell will burn out with the first fire.

It was really windy and I had some problems with keeping the newspaper stuck down on the dome, and it kept drying out so I had to periodically mist it with the hose, and finally just put a block of wood on top of it.

I had all of my buckets of mud that I had saved from Sunny 1.0 and it was wet and ready to use so I got started building the oven.

I picked up big handfuls of mud (sand and clay in a 1:1 mix) and started going around the bottom of the dome, building a wall roughly 4 inches thick.

As I moved around the oven in a spiral, the wall got higher and higher. I used a piece of 2 x 4 to firm and shape the wall as I went, and made every effort to keep it a consistent thickness all the way up. The wind helped to quickly dry the mud and stiffen it, but I realized there was some slumping on one side (the mix used there may have been a little wetter than ideal) and so I slowed down the building process to allow the mud to set up a little and gain some strength to support the weight of the wall.

This took the better part of the day and as I got close to the top, I realized I was going to run out of mud before I ran out of dome, so I gathered up a bunch more clay from a hole Greg had dug the other day, and watered it down. I added sand and spent at least an hour trying to get it homogenized by hand. By the way, I don't recommend this method. My hands are still extremely sore, and I can barely type.

I managed to get most of the clay and sand incorporated together but not before using more water than I should have, leaving me with a very wet mix.

I decided to let the mix set up overnight hoping that the clay minerals would rehydrate and take up some additional water into their actual crystal structure, making for a smooth mix with plenty of strength. The two separate mixes may be a problem when I go to finish the oven if the new mix and the old don't bond together well, but I think I have a solution for that. I have a bunch of 4 inch galvanized nails that I'm going to stick into the existing shell and use them as a kind of rebar or "key" to tie the two together. It may still crack but since the insulation layer will be going over it, I'm not really worried about heat loss, just the strength of the shell.

Today (Sunday) I hope to finish the inner shell, finish the insulating layer, and cut the door opening. I think I'll leave the sand inside for a few days just to support the "weak area" as long as possible.

Once the insulation layer is finished I'll let it set up for a couple of days, and then mix up a third layer of mud that will include fine chopped straw, sand, and clay. This will be the finish or plaster layer and the texture will allow me decorate it either by sculpting a design or adding some pebbles in a cool pattern. After that, the only thing left to do is put on the stucco textured coating on the vertical faces of the cinder block foundation, and then paint it. Oh, and start cooking pizza...

The last picture demonstrates the difference in color between the Old Sunny clay and the new clay dug out of the ground a couple of days ago. The sand to clay ratio is about the same so hopefully it will shrink pretty uniformly as it dries. My only concern is that the Old Sunny clay has been subjected to high temperature (but not high enough for it to undergo vitrification obviously) so it may not respond the same way to firing the oven.

Guess we'll find out. I can always start over again. It's only dirt, right?

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