I am going out on a limb in the forum as I don't have an observatory but I want one. I don't have much room so a small dome would be perfect. If I look at a screwdriver, I might lose a finger so I am looking for a recommendation to get one installed. That includes a slab with pier.
For dome options, hit up Diego and Paul at https://www.siderealtrading.com.au/. They are reps for some pretty impressive bits of kit. They also offer a 5% CAS member discount...
I’ve ordered a Nexdome 2.2m dome from Sidereal Trading ( Paul and Diego ) and putting it on a hardwood deck about 400mm above ground level
Concrete slabs can cause moisture issues etc
Mine arrives in October/ November
Check out a Nexdome !!
Interesting theory. The major/pro observatories of the world use steel and concrete as opposed to wood. Besides, after a layer or concrete primer, Dunlop ardit levelling compound, concrete/flexible paint w’ added sand for foot grip and a dehumidifier running on a timer - moisture will be a non-issue.
The major pro observatories of the world sit on concrete structures 5 to 10m metres thick , not 75mm thick sitting on your back lawn
My garden shed sits on a 100mm thick concrete slab and there’s always moisture be it damp or cold damp all year round at night and worse after rainy weather and it sits on a slight sloping well drained block
The most efficient and cost effective way to minimise rising damp or moisture is a ventilated air space between the ground and the structure
Moisture will be a non-issue. We have the technology. I’d prefer to spend $90 on this v.s. $1k + on an elaborate raised wood frame. A dehumidifier on a timer is still required in both scenarios. https://www.bunnings.com.au/dunlop-4...ofing_p6820176
The major pro observatories of the world sit on concrete structures 5 to 10m metres thick...
The major pro observatories of the world sit on concrete structures 2 to 3m metres thick.
The major pro telescope mounting systems (piers) of the world sit on concrete structures 5 to 10m metres thick.
The use of "damp proofing" (look it up, usually a layer of plastic like material) under the slab stops moisture moving into the slab. Even a concrete pier really requires damp proofing.
Speak to a qualified builder.
Having said that I used steel RHS for floor joists around a tri-pier system.
Last edited by theodog; 27-08-2020 at 07:14 AM.
Reason: Pic added
I did discuss a dome with Siderail trading but to be honest, flying two people up to Canberra to install the deck (his preference) and install the dome was a bit expensive at about $2.5k. Couldn't do it now because of the travel restrictions anyway. Their advice was to put (concrete) a pier in and to place the dome on the deck to get everything else off the ground. If overseas travel is still off the cards next year, I might take their offer up assuming my wife says ok to remove the rotary clothes line in favour of a wall mounted one.
I’ve ordered a Nexdome 2.2m dome from Sidereal Trading ( Paul and Diego ) and putting it on a hardwood deck about 400mm above ground level
Concrete slabs can cause moisture issues etc
Mine arrives in October/ November
Check out a Nexdome !!
Sorry Martin but I have to call you out about moisture issues and concrete.
If there were moisture " issues " with concrete why is it used so much in residential ( and other types ) of construction.
If it has a moisture barrier in place and isn't subject to water runoff, there are no problems with moisture in concrete slabs.
If you have experienced moisture issues then most likely the person/s doing the work did not understand what is needed, perhaps they watched to many episodes of The Block?
I have a 3m dome, the timber floor level is about 800mm above a concrte slab that is dry, it has a moisture barrier installed as well has no surface water run off.
Sorry Martin but I have to call you out about moisture issues and concrete.
If there were moisture " issues " with concrete why is it used so much in residential ( and other types ) of construction.
If it has a moisture barrier in place and isn't subject to water runoff, there are no problems with moisture in concrete slabs.
If you have experienced moisture issues then most likely the person/s doing the work did not understand what is needed, perhaps they watched to many episodes of The Block?
I have a 3m dome, the timber floor level is about 800mm above a concrte slab that is dry, it has a moisture barrier installed as well has no surface water run off.
Ed
Ed
In regard to concrete slabs for small observatories I did comment by saying they “can” cause moisture issues not always “do” cause moisture issues
Factors that affect moisture in ( 75mm to 90mm thick ) backyard slabs typical of what you would pour for a small dome are -
1/ Soil type
2/ slope of land
3/ height of water table
4/ amount of rainfall or annum
5/ drainage
6/ location eg low lying area or up high on a hilly property
7/ whether it has a water proof plastic membrane under neath
8/ Near any retaining walls
9/ Neighbours run off
10/ And the list goes on and on
My Dome will be located 200m from the beach on the south coast NSW which generally has higher rainfall than west of the divide. My drainage is not that good so I’m opting for a raised timber hardwood deck about 400mm off ground level with 4x 200mm diameter concrete piers for the 3 tripod legs and 1 central for future pier mount. The 4 concrete piers will finish 5mm below the deck level. 60mm holes will be drilled through the deck centrally above each pier for the tripod feet. The Dome floor will be 18mm thick 300 x 300 interlocked poly tiles and rubber backed ribbed nylon dark grey carpet laid wall to wall and cut in
Good luck on your build, like most who have an observatory say when they have one, it just makes it so easy to use the hardware I should have done it years ago.
No offense meant ( or taken ) I'm coming from a building background ( 40+ years licensed builder ) all the things you mentioned can be addressed using good design, the biggest problem I see in any on-line forum with observatories is the slab often extends OUT past the line of the building, the dome / warm room cladding should extend down the side of the slab, not a lot, 20mm is enough 50mm is better. The other issue is lack of plastic membrane under the slab, contrary to popular opinion, this does NOT need to come up the outside edge of the slab and then under the wall bottom plate but it should be under the slab.
Get those two right ( and don't have the finished ground level higher than the finished floor level of he slab ) and you won't have problems with dampness.
Of course, if you don't get it right you will have damp issues, still to me it is better than a timber deck 400mm above the ground where water can run under the deck, rot the timber, harbour termites ( BTW, if the slab is vibrated it forms part of the termite barrier, unfortunately, few in the building industry vibrate slabs hence they do not form part of the barrier ) and worst of all have moisture rise into the observatory - where all the expensive hardware is.
It's not much more in cost but well worth it as I ordered 50mpa concrete mix do it would form a natural barrier to ground water. I have absolutely no water inside in the floor. Condensation is always a problem for me as I live right near the wetlands. I use a dehumidifier to protect the gear. Oh and my slab was slightly thicker with 4.8m3 http://www.iceinspace.com.au/forum/s...&postcount=137
I see you went belt and braces - 50Mpa and plastisc
I like your formwork as well, perhaps a little overdone but no worries about any blowouts - perhaps the one area most people have problems with during the pour.