The Thermal Layer, Finishing The Door And Arch

While we left the thermal layer to cure I decided to finish cutting the door before the cob got any harder. I had made a frame for the arch in order to support the bricks while I was laying them. I made sure that the outer arch was about two inches taller than the height of the oven door. I measured out centered and marked the final height of the door on the oven. The I used the arch template to mark my curve of the oven door. Then I decided I wanted a one inch reveal of the oven door. OK I know more fancy words. The reveal is the part of the door the you see that sticks out past the bricks. It looks like a frame that is visible inside the frame of the bricks.

I built the frame with a 2x4 base and 1x2 risers and arch. In order to get a nice smooth curve I made kerf cuts 1/4 inch apart 1/2 inch deep with a table saw. Then I nailed the arch to the center riser and then the end risers. I also ran the outer risers along the blade of the table saw to cut the ends of the arch smooth and in line with the outer risers. This technique created the template, curve and corners beautifully. However I ran into a small problem when I used the form to make the arch. This form needs more support than only the center riser. As you can see in the picture below the weight of the bricks flattened out the sides of the curve. So I would recommend adding one or even two more risers on each side.



Yes that is another one of my kids. Jason was trying to convince me that the oven was big enough to be his new room. You can also see what I was talking about where the curve flattened out on each side. You can also see the inner door and it's reveal that I was talking about.

OK now on to the cutting of the door. I wanted to find something to make a clean smooth cut for the door through the cob. I realized that I had a MultiMax vibrating tool that had blades designed for cutting grout and concrete. I figured this would be a good tool to try. The MultiMax worked like a champ. The only issues I had was that I had a tendency to cut at a downward angle because of the bolt on the bottom of the tool and holding and working that much vibration killed my wrist. I found that if I ran a shallow cut or two into the thickness of the side walls of the door then went back from the front and cut out the opening in layers it worked very well. If you wanted to use a hacksaw at this point instead of the vibratory tool you could, but that MultiMax cut the time down considerably.

To build the arch I started from the outside and worked in to the center. Leave the very center brick for last as this is the keystone. This is the brick that will hold and lock the arch together. I used about 1/2 inch of cob mortar between the bricks and the pressed the keystone into place. Also remember to fill all around the top of the risers to provide a solid bed of cob to lock the arch in place. It sounds harder than it is. Leave the arch support in place for a day or so the mortar can harden. There you have the first brick arch I ever built but, it won't be my last.