Dickson finished the four walls that serve as a template. He used a rebar form to get the catenary arch shape to each wall. Above he has started on the first course that lies on top of the wall and where the strings are attached.
After looking at it I thought it would be better to build the horizontal course at the same time so we get a better bond and better weight distribution into the bottom of the groin. this is where about 2,200 kgs has to be distributed, hopefully over 4 bricks.
We are not sure the limits we can go with the horizontal courses without form work below, but we stop at this level.
The most difficult part to figure out was cutting the groin pieces. Hopefully the next pictures will give you an idea.
Dickson has marked the header side by using the string, and the stretcher side not in view by using a brick dry laid in place.
After in place with mortar it looks like this.
And a close up.
Why do we extend the brick out past the line? It would be another complicated cut, and cutting bricks destroys the smooth surface of the header. seems to look better this way.
It is a shame to cover this , but we need to make it waterproof.
Now we finish the arch over the walls. and start to the vertical courses parallel to the wall. This is not the way groined vaults are done with form work.
Butter a brick with clay/sand mortar 5mm only. tap into place and hold for 5 seconds and it will stay up until you finish one course.
Lay 3 courses and move to another side. No strings yet. build the arches up to 1 brick away from the groin.
After pointing.
