Step 5 Construction of the bell
Drilling holes
Up from the second layer, the corners are not only glued, but also additionally secured with a screw. For this, holes with a diameter of 6 mm are drilled on the longer parts, 25 mm from the side. In the shorter parts the holes are drilled exactly in the middle of the ends; that's where the plugs come in.
Drilling is done with an ordinary concrete drill, and a diamond drill. Working with diamond drills is shown in this YouTube-video.
Precise marking is required. Do that with four lines around the hole, as shown below. Drill the hole in the longer part from both sides.
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Second layer
Before you finally put the layers in place, you first make a test fit. On a flat surface you put the layers together without glue. Test that the screws will be tight. They should not be too loose, but certainly not too tight either. If necessary, you can drill out the hole a bit, or use other plugs.
The second layer is laid on top of the first with cement mortar 1:5 (1 part portland cement to 5 parts sand). Height of the mortar layer is 9 mm.
Place the four concrete blocks on the mortar one by one and glue the corners. With the help of clamps you press the parts exactly into place. Measure the two diagonals to make sure it's exactly square. If necessary, use the large clamp to correct. Once everything is square and level, tighten the stainless steel screws.
Now cover the top of the firebox with Superwool.
Third and fourth layer
Place spacers of 10 mm high in the corners an place the four concrete blocks on top. Use a level to check whether they are exactly above the previous layer.
Glue them together and secure with screws. Make 9 mm high spacers from iron and replace those of 10 mm with these; the concrete blocks will rest on these spacers.
For layer 4, make a small scaffold on both sides of the stove so that you do not have to lift above your head.
Fifth and sixth layer of fire concrete
Layers 5 and 6 are made of fire concrete, as described in Step 2. Only when it has hardened properly you drill the holes for the screws. Make a test fit first.
Once the bell is completed you can fill the joints with cob:
1 part clay powder mixed with 1 part fine sand, and then mixed with water. Use masking tape to get it nice and tight.
You drill the first 2 mm with a regular concrete drill, without the impact function. Drill the next centimeter with the diamond drill: this allows you to make very precise corrections. The rest can be done with the regular drill, and then with the impact function.
Superwool 35 mm wide
Overlap
A nut can also serve as a spacer
