As mentioned earlier, I needed to make sure that the top of the concrete around the pier
was 0.5" lower than the surface of the pad concrete. So I started on the pad, laying it out and
creating a form for the concrete before pouring the pier concrete. Because the dome I was expecting was
circular I designed an octagonal-shaped pad. This turned out to be quite fortuitous later when I had to
construct a frame for the observatory I eventually built.
The pad mapped out with the turf removed
I left the turf around the pier hole for some time to prevent its collapse at the top. The
concrete for the pad is 3.5" deep. The ground proved to be uneven and on a gentle slope on the
north-south axis. Hence, in the image below, the boards around the north side closest to the camera are
below the grass surface whilst those at the north side are well above. It is very important to have a
level pad if having a dome for the smooth rotation of the dome on its walls. It is possibly slightly less
so for other types of observatory. I didn't bother with a hard core base, the sand was tramped down and
very firm. It wasn't going to move.
The pier and pier hole construction
The concrete was poured into the pier hole with the pier held in place with some heavy
pieces of wood and bricks. I had two builder's levels to ensure that the pier plate remained level at all
times. I wasn't concerned about the pier being vertical, this doesn't matter. What does is the surface
onto which the scope will sit. I also roughly aligned it north-south. However, you'll remember that there
was provision for adjustment later with the second top plate.
The form for the pad complete
When the pier plate of the pier was welded on I had two holes made a quarter of the way up
from the bottom (half way in the section in the hole) opposite each other. This allowed the concrete to
pour into the pier and be one with the concrete on the outside of the pier. I also placed some steel rods
through this hole. Hopefully these two measures will ensure the vertical stability of the pier. I also
stood the pier on a couple of small bricks to allow concrete under the pier rather than let it sit on the
sandy base of the hole. Concrete was poured into the access hole at the top filling the pier to just
underneath this hole. Over the top probably, from what I've read some of you Americans may not think
so :-) but this 'bird table' isn't going anywhere in my lifetime - or the next!
The concrete laid and signing my name
Electrical cable was run from the house inside a plastic conduit and buried under the lawn
and comes out of the pad. You can see it here sticking up above the concrete and wrapped up to prevent the
conduit being filled with concrete. At this stage I had not planned where I would take the electricity
wires (to the pier or observatory walls) so this seemed a fair compromise. You may want to consider more
than one electricity supply and another conduit containing serial, network or telephone cables if you
intend to do some remote viewing using CCD or video cameras with your computer in the house. I always
planned to use a laptop in the observatory so this wasn't necessary for me.
A membrane was placed over the base, stones having been removed first. Thin boards were
placed over the pier concrete and the concrete poured. A single layer of chicken wire mesh was placed in
the concrete about half way down to strengthen it.
The pad finished and set months later
When the concrete had cured, the form was removed. The form around the pier concrete left a
0.5" gap between the pier concrete and pad concrete. As you can see here, the pier concrete is lower
than the pad concrete so that when flooring is installed it doesn't touch the pier concrete. A large
flower pot covers the electrical source, I had placed a metal clad RCD double socket here as I was using
this pad for two years waiting for the dome that never arrived.
Before constructing a concrete pad you may want to look at HomeDome's site which provides an excellent document entitled "At
Home in a Dome" which you can download. In it, there are extensive details on how to construct a
concrete pad and pier construction designs.
So that was 1999. As I say, the dome didn't arrive, so I started to design something
myself. I looked at lots of sites on the web - the best place to start then was Bill Arnett's "List
of DIY Observatories" (now down). It quickly became evident to me that with my limited DIY and
construction skills what I required was a ready-made shed of some sort I could adapt. It also seemed the
cheapest and quickest way to proceed. But most sheds were of the wooden garden variety, thinly clad, no
appreciable frame and with roofs that were not easily adapted to a roll-off design. Then I came across a
site that changed everything.