Step 5  Lower part of the riser and assembling the core

Cut two riser castings to the same height as the port, less one mm to account for the Moviset at the bottom of the casting. This height should be around 251 mm, but it should be measured. Best is to mark a pencil line at the exact height, then use a grinder to cut along the line such that the pencil mark just disappears; this will give the 1 mm allowance for the Moviset. One edge of these two riser castings needs to be cut at 45° to fit against the firebox port. Mark the 45° line across the two ends and draw a guide down the
outsideface of the riser. Clamp a 45º guidelath on the inner face and carefully cut with a small grinder. (Short upper sections will be glued in later to bring these riser segments up to the full height.)

Each of these cut riser castings can then be glued with Moviset to two others using a 135° lath to set the correct angle (as shown in the picture). Leave these assemblies to harden for a while, then glue them to the firebox port. The tops of the cut riser castings must be flush with the top of the firebox port lintel. Now, before closing the riser with the final casting, the heel must be fixed in place at the bottom of the riser with some glue, filling up (completely!) the space underneath it with cob or glue. Ensure the correct position/angle by inserting a lath cut with a 45° end into the port through the firebox. Now close the back of the riser with the final riser casting using Moviset.

Three short sections of riser casting sit on the port lintel to complete the lower riser. It is important that the inner face of the middle casting is flush with the rear of the port lintel to ensure a smooth interior finish to the riser. Also take care that these small pieces are not too tight. If necessary, cut away a fraction until they make a loose fit (with space for the 1 mm of glue). Adjust all angles and ensure the riser is symmetrical, vertical, and sealed all around while the Moviset remains workable.

Now leave the core assembly to set hard before transporting it to site. At this point you can already glue the upper riser together. Like the bottom part, half of the castings are 350 mm of length, the other half 330 mm. Making it this way, the upper part will fit exactly in the bottom part.

Also you can already glue together the firebricks for the upper bell (see Step 9).


grind in an angle of 45º

First cut two bricks the same height as the port,

then grind them in an angle of 45º.

... then glue the heel.

Glue these castings together, using a 135º lath (picture) ...

... then glue them on the bottom and onto the firebox port ...

... and the 3 short sections

(glue joint at the bottom is 1 mm)

Finally, glue in the back riser casting...