Just wondering, is there any cons with building a concrete pier as part of a slab?
My idea was to dig a 1m x 1m x 1m hole, pour concrete in it and then as part of the same pour, pour a pier in at the same time, with rebar throughout the structure. Essentially, the whole structure would then be one block. Then, I would have a second slab isolated by a few centimetres (to avoid any vibration should I walk into the observatory while imaging) around the pier/block for the floor/base of the shed.
The observatory will be solely for remote operation.
The pier that I have at the moment is too tall for the Absco shed that I've bought, unless I build a 2-foot high structure to mount the shed to.
That should work fine H. I haven't built any telescope piers but I have built 12m high columns where the adjoining slab needed to be separated. You could pour your pier/block combo then once set, wrap it with one or two layers of AbelFlex with the tear-off strip to the top. Once the slab has cured you remove the tear-off strip and the fill the gap with some Butyl mastic this is to stop moisture coming up through the gap but is flexible enough not to transmit vibrations.
I did mine that way.
Though I didn't put in a top slab, I just gravelled the area.
I used a mains water pipe as a former, so I now have a pretty blue pier that has zero deflection and zero resonance.
I made it a little taller too so it's about 5 foot high.
Just going by the visuals of the pier installed back at our home in Queensland, the top of the telescope was about 2 metres high. The shed has a skillion roof, 1.5m on one side and 1.2m on the other. So, my pier is going to have to be tall enough to sit the scope comfortably somewhere in between those two figures.
Thats exactly what I did H. Hover a tube over a hole in the ground and just start pouring. I used quick set concrete. That helps stop concrete spilling every where when you start on the tube, but dont muck around, do it all in one go, fast is the key . You dont need reo and all that palava, just remember to stick threaded rod in the top for the mount before it dries . This is the cheapest way to get a base and pier, and its all in one go. The tube can be what ever doesnt mater, its temporary. I used wrapped gal sheet. Cardboard would do.
I threw an old shopping basket in the bottom to rest the pier on and drilled two 4 inch holes in the side and popped in a couple of bits of rebar.
I dropped in a 4 inch pipe in the pier centre so that I saved a couple of bags of ready mix - photos on request.....
Fred, fantastic. I'm going to come up with my formwork design as soon as I get a chance.
Jen, I'd love to see pics!
Marc, awesome. Where did you get the Sonotube from? I'm trying to source that or a Formatube (plastic one that doesn't leave swirls on the pier) locally. Failing that, I'll just build a rectangle column/pier. That way, when we move out, the next person who moves in has an obelisk in the backyard as a feature.
My temporary pier was planned to be much much smaller than final solution.. it started as as 75cm deep, 40cm in diameter hole, filled with concrete, and steel pier fixed with 6 cast-in screws..
However, temporary solutions very often turn into almost permanent ones..
I did polar alignment 3 years ago.. and never needed to touch it since.
I poured my footing and pier in one continuious operation - all of It's hand mixed in a 20 litre bucket. The footing was 700x700 x 700 and tapered in a pyramid shape with It's wider at the bottom. Drove some galvanised steel angle into the bottom, poured to ground level, inserted reo during pour, used three reo rods up inside the pier that go through the footing. Very strong. My pier form was simply the largest pvc pipe I could find and It's worked great, never had to be removed, leaves a nice smooth ivory finish.
Marc, awesome. Where did you get the Sonotube from? I'm trying to source that or a Formatube (plastic one that doesn't leave swirls on the pier) locally. Failing that, I'll just build a rectangle column/pier. That way, when we move out, the next person who moves in has an obelisk in the backyard as a feature.
H
I got it from Marcus at the time. He had leftovers from his own obs so he gave me a piece.
Mine will have a bird bath or a pot plant on it when I move on...
. You dont need reo and all that palava, just remember to stick threaded rod in the top for the mount before it dries 
. This is the cheapest way to get a base and pier, and its all in one go. The tube can be what ever doesnt mater, its temporary. I used wrapped gal sheet. Cardboard would do.
