Step 4  Making the lower section of the bell and the core’s firebox

Lower section of the bell

Place the cast bottom slab in a suitable place for working. It must be level. Construct the first layer of concrete blocks on the bottom slab. Use mortar with cement : sand in proportions 1:5. Take care to control the dimensions (height is 170 mm + 10 mm joint) and make sure the structure is square and level.

This lower part of the bell is now ready for transport to the site.

Making the firebox

This building description assumes that the core is built off-site for transport to the final installation location. The core is built up on a transport board that must be sturdy enough to carry its weight. A sheet of 18 mm melamine-coated chipboard or similar works well.

Place a pair of battens parallel on the transport board and lay a couple of the bottom firebricks in place between them to get the correct spacing. Fix the battens lengthwise on the transport board. This structure will hold the bottom firebricks in place during the build.

Construction work is easiest if the transport board can be placed on a workbench or raised to a similar height.

(An alternative method is to construct the core in-situ on top of the bottom slab.)

    About glueing with Moviset

You are going to glue the core together with Moviset or a similar refractory glue. Open the Moviset bucket and pour off the covering liquid, which can be saved for later use. Mix the glue well until it has the consistency of beaten butter. Add a little of the poured-off liquid if necessary. At the end of a day’s work with Moviset, replace the liquid to prevent it setting in storage; add some extra water if necessary.

Spread the glue over the surfaces to be glued: both surfaces need to be covered completely (not thick, only ± 0,5 mm). There must be no air spaces when the surfaces come together.

Moviset sets within 24 hours when the temperature is 15°C or above. At lower temperatures, setting time is not yet known, but it may be much slower.

    Bottom firebricks and firebox

This building description assumes firebricks with measurements 220 x 110 x 30 mm, and for the bottom of the core 220 x 110 x 50 mm. For the bottom you need four full firebricks and one cut firebrick.

Exactly in the middle of 3 (full) bottom bricks, you cut out a notch of 40 x 20 mm. This will form the slot that accepts the floor channel.

Butter one edge of the first firebrick with Moviset and lay it on the transport board. Butter two edges of the next three bricks and lay them in place. Carefully apply pressure across the four firebricks until the Moviset begins to squeeze out. A large clamp helps with the application of a little pressure. Now measure for cutting of the fifth firebrick; the total length of the core base must be 506 mm. Cut the final brick to achieve this total length (remembering to take account of the 1 mm of Moviset). Make sure the bottom bricks are level and let dry for a short time.

Glue the walls of the core onto the base: three firebricks placed vertically for the left, three for the right side. Try to make sure the firebricks that will be visible at the front of the core are all flush; this is simply an aesthetic consideration. Allow to harden for a short time.

Next form the port at the rear of the core. Glue the two vertical port castings and then the lintel casting across the top. Careful measurement is necessary here. Most important is that all of the rear port castings are perfectly vertical and aligned so that they form a flush surface (for later installation of the riser). The top of the port lintel should be level. The port opening must be 40 mm wide.


1. Transport board

2.  Floor bricks

3.  Walls, port bricks

4.  Upper port brick

5.  Top bricks

6.  45º bottom bricks

4 mm space

Finally, glue on the firebox top, which consists of one casting, one whole firebrick, and one firebrick cut to size such that the front of the firebox is flush. The part-firebrick goes at the front with cut face inwards to ensure that top joints are offset from the wall joints (for added strength) and to preserve the aesthetics of the front. (Remember that the front edge of the firebox is visible to the end user when the Roquetinho door is opened.)

The 45º chamfered bottom bricks can then be glued into the firebox, ensuring that all gaps are filled with Moviset. Leave open a space of 4 mm between the bottom bricks and the front of the firebox. This is where the floorchannel’s frontplate will fit in.

The 3D Sketchup file for the core is in the Roquetinho-folder.