Tuesday, July 03, 2007

Il Duomo

Last time, we had just completed another course of stone work. So we start off by filling the top three or four inches of the foundation with concrete because, if you recall, I was determined to make a floor that would not cave in. The first layer of concrete had vermiculite mixed in for insulation -- a nice idea, but poorly executed. I don't think the vermiculite layer will be thick enough to have a material insulating effect. We made the concrete flush with the edges of the foundation.



Next I added a ring of bricks (salvaged from the yard) and two concrete pavers. The idea was to create a circular sandbox on which to lay my firebrick floor (sans mortar).



I dry-stacked a firebrick door frame using angle irons (as suggested by Kiko Denzer). I really wanted to make the entrance point of the oven a little more civilized this time.




I've been dying to try a little brick masonry and this seemed to give the dry-stacked firebrick arch a little extra support. I am hoping the mortar will be insulated from the most intense heat so that it will not degrade too rapidly -- even if it does, it won't seriously undermine the structural integrity of the oven. The paving bricks are stacked in the center to hold in place a piece of drywall that will prevent the sand form from spilling through the door.



I don't have a picture but I laid sand on the concrete floor until it was flush with the two front concrete pavers. This picture shows the firebrick laid on top of the sand. I took some scrap bricks and laid them to the sides of the floor to keep things in place and to support the clay walls.



We spent a surprisingly long time forming the sand mound. Kiko cautions that the form should rise very steeply and then round off gently at the top. For some reason, the temptation is to build a pointy form, which makes for a poorly shaped oven. He says to aspire to a pregnant belly shape, which is probably why it took me so long. Try though I did, my best effort was still a pretty scary looking pregnancy.


Once you sculpt a beautiful sand form, you promptly cover it up with ugly wet newspaper. Mine declared the immigration bill defeated. This helps form a clean break between the sand form and clay to facilitate removal of the sand.



We mixed dry clay and grog -- this is where I part company with purists like Kiko Denzer. I used one part Redart Clay, one part Hawthorne Fire Clay, one part 35 mesh grog and one part course grog that the ceramic supply store had lying around and didn't know what to do with. I measured the "parts" by volume not by weight. In the end I used 100 pounds of Hawthorne, about 85 pounds of Redart and 175 pounds of grog. Kiko uses earth and sand.


After adding water and mixing with our feet, we formed wet bricks.

McGee, desperate to be a part of the process, kept dropping his tennis balls into the clay mixture.


We encased the sand form with the wet clay. I made two larges batches of clay -- which ended up being about three bricks short (not reflected in the photo below - which was more like the halfway point). This was very frustrating. I made a third small batch of clay to top off the crown.

Once formed, I scored the sides with a trowel so that the next layer would have something to grip to.

3 comments:

Ann said...

It is a very beautiful dome (il bello duomo?), and yes, a very scary looking pregnancy!

Liz K. said...

Um, wait! Did you guys get a dog???

Eric said...

This is great. I hope you are going to keep adding photos as you progress. I'm looking forward to seeing how it all turns out.