Step 9  Upper bell construction, steel top, frame & door unit

 

  Upper bell construction

Building up the rest of the bell it is best to have some kind of guides. One method is to clamp laths to the four corners at the bottom slab; mark them with the layer heights (which are height of the concrete blocks + 10 mm joint for layers 3 and 4, and height of the firebricks + 7 mm joint for layers 5 to 8). Use spacers to bring the laths 2 mm away from the bell and level the laths carefully. String can be used between the laths to get each layer exactly level.


Lay the concrete blocks for layers 3 and 4 using cob.


Laying masonry with cob is really different from making
it with cement. Do some tests first; the cob shouldn't be too dry or too wet. Put a "roll" of cob on the previous layer and press the blocks down onto it. There must be no gaps!


From the 5th layer you use the firebricks. Before starting to lay these, you glue the vertical joints of the bricks that come in the middle, using Moviset, and let it harden for a day. Only at the corners you use cob for the vertical joints. This way, it’s easier to repair whenever there are cracks in the upper bell, once you use the stove. A crack is repaired by making the cob wet again and push some new cob into the joint.


Lay the firebricks for layers 5 to 8 using cob; the horizontal joints here are 7 mm.


  The top frame

Lay the steel frame over the bell’s top using cob. Carefully check the

1 mm margins at the sides. Remove the cob that squeezes out. Height (cob + steel) should be ± 10 mm.


   The steel top

Now lay 4 strips of superwool on top of the bricks, and place the steel plate. There’s a margin of 4 mm at the sides between the plate and the frame.


 

glue

cob

   Placing the frame & door unit

Take the frame and fit it over he protruding front of the firebox. Outline the exact places on the stove and drill holes for the plugs and screws. Fix the frame and attach the door to it.


   Trapdoor

One last thing: placing the trapdoor. Once a year it might be useful to cut it open and clean the inside of the stove. Fix it (airtight!) with sealant.