Foam triangles were cut using a hot wire on a large bench with a jig to get exactly the right kerf so tiles will join at the right angle. More tiles added gradually, starting with the very top pentagon at the dome apex.Note that in a geodesic shape, the triangles that make the pentagon are slightly different in dimensions to the hexagon tiles. This is what shapes the structure into a nice hemisphere. For glue I used Selleys 'No More Nails' which works as a glue in two handy ways. First as a one application glue, or the method I used, as a contact adhesive. Surfaces were smeared with the glue then left to semi dry. Then brought together. It forms a very good bond, which has not deteriorated in 10 years.
Each node where five or six tiles met was also smeared in a layer of this glue to strengthen the joint. I also wrapped each joint both inside and outside with gyprock self adhesive joining tape. Glue was smeared over this tape and formed a nice webbed, strong join.
A note about glues: Some purpose made glues for foam dissolve part of the foam on contact. These are no good because some of the integrity of the join is lost due to surface area of the join being compromised. After trying quite a few, and not having the budget for the best, which is a 3M product, No More Nails, in caulking gun cartridges was the best solution I could find. Next came the dome slot, which had to be a perfect set of curved plywood rails if I ever wanted a door arrangement to slide nicely along it. The design of the doors and rails was basically made up as I went along. In hindsight, there are a few things I would have done differently with the doors but I had never made a dome before. With many of the outcomes it was the best thing I could think of at the time and I think it has stood up quite well.
Doing the slot cut was quite difficult because the line follows a very convoluted edge of triangles. It came down to firstly drawing a rough line and cutting with a boxcutter blade. Then trimming using a straight edge until both sides of the slot were cutting through the same points on the same respective tiles and the slot was parallel. The plywood slot was layered with several curves in a sandwich so that it would have strength for the weight of the doors. Both outer and inner running surfaces were routed to make a smooth surface for wheels to run on. Curves were then glued directly to the foam using a large amount of glue. Dowels were drilled into the foam to attempt a tie into the strength of the overall shape. Overall, the slots contribute to holding the shape of the entire hemisphere, but the foam did that by itself anyway. As a test, very early in the construction, I laid my entire bodyweight over the top of the dome before the door slot was removed. Spheres are one of the strongest shapes, even when made of foam :)
The Papier-Mache experiment
Joe from Oregon clad his dome in a concrete stucco or render. In hindsight again I should have gone down this path. But in the months that this project flowed I tried little experiments with cladding. Obviously the best was to fibreglass it but that would cost big dollars. I could have just bought a Sirius dome or pod for that kind of money. Concrete was my main option but my attention was diverted to my scale model I had built before construction had started. I had made if from cardboard but glazed it with a smothering of Aquadhere wood glue. This had formed a very hard surface when left in the sun for several days.I tried a multilayered papier-mache using newspaper on an offcut of foam. I tried a multilayered canvas on another. Another using the cheapest calico fabric I could get from a craft wholesaler.
The best one that dried the strongest when drenched in a solution of woodglue was the papier-mache. Here I made a decision based on: if it all failed then I could rip it off and render in concrete anyway. So from this point on I spent literally weeks adding layers of newspaper to the foam shell. One layer East-West, the next North-South. I did this because newspaper has a grain. It tears easily in one direction better thatn the other. Same as plywood really. After sun-drying many layers and wheeling the dome in and out of the shed it was starting to form a very strong skin. As long as I did a very good job of weatherproofing this skin it should last for years. It took on the feel of a very tightly strung canvas skin and was very hard to dent even with a sharp object .