Step 1.3. The form (mold) for the hypertufa.
Hypertufa (in a sense) is a lightweight concrete.
In order to cover the top of the head with hypertufa I had to make something to hold it in place until it cured (set). This involved covering the current structure with polythene (plastic) sheet to stop the hypertufa falling through the support structure, and also fixing a wall (form) around the sides to stop the hypertufa running over the sides.
I stapled and taped some polythene (plastic sheet, such as plastic rubbish bags) over the top of the head and pulled it tight.
Then I ran some tape over the polythene along the top of the inner support structure frame-work, and stapled that as well to ensure extra strength
Then I made a form around the sides of the head to contain the hypertufa (lightweight concrete).
I made the forms out of spare plywood that was 5/16" (7mm) thick. The forms were discarded after use.
Below is the pattern for the temporary form pieces that went around the sides of the head.
The line spacings on the grid above represent 1" (25mm).
Once cut, the form pieces were screwed to the sides of the head. The top of the forms sat a little over 1½" (40mm) higher than the sides of the head.