Stage 6: Installing Arch Forms

The arch forms are installed on top of spacers set, unfixed, on top of the box forms. The are shimmed plum but are only held in place by the pressure of the bags around them.

arch forms installed

Note the depth of the arch forms is the same as the box forms. This is because they must provide both an arch surface for the vertical door/window wall on the outside, and an arch surface for the dome as it begins to close in.

arch forms installed top view

A close up view of the door form.

door arch close up

Here is a model of what the dome is supposed to look like when the bag work and plaster is all finished. This gives a clearer idea of how the door and window openings will look like. The final structure will end up having slightly more extended openings as we decided to add a little more mass than the initial design. Looking back, it was probably was not necessary but this is an experiment after all.

model and arch forms

When using unstabilized soil, using fanbags around the arches is probably the strongest construction method. To make fanbags, a box-form was used where the bag was filled and tamped completely, and then set in place on the structure. Fanbags are not as heavy as a regular bag. And, being that they are solid makes them easy to maneuver. If possible, it is recommended that one makes the fan bags on the structure. In our case, however, the dimensions of the structure were small enough that it made more sense to mass produce these on the ground while other work was being done on the wall.

box form for fan bags

Two fanbags have been set in place around the window. Note the continued use of the lathe, wrapped around each layer.

fan bag close up

A view of the first fanbags from above.

fan bag top view

The bagwork continues. Openings in the domed part of the wall are technically challenging. But they sure look cool as they come together.

fan bags continuing

The end of a long day.

end of the day, fan bags continuing

We’re getting closer to the top. Another couple of layers and we’ll be ready to install the keystones.

nearing keystones

Because of the dome wall getting smaller, the number of fanbags increases. Note the gaps in between the fanbags. These irregular openings are filled by setting a bag directly in the gap and filliing and tamping to shape.

nearing keystones top view

Now, the keystone bags begin. Just like a brick or stone arch, the keystones are what keeps it all together. These are hand shaped directly in place, three bags at a time, up on the wall.

starting keystoneskeystones keystones finished

Tada! There you have it. The inside keystones of both windows were finished first allowing for the dome wall to be continued independent of the outer keystone work.

begin outside keystones

Now let’s finish off the dome!

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