Mahogany Flooring for Outbuilding?

I'm preparing to build a small astronomical observatory at my home <http://www.davidillig.com/observatory.shtml . A rotating dome will rest on an eight-sided, four-foot high structure built conventionally of 2x6's (treated sill plates, standard studs and top plates). The sill plates will be bolted to a concrete pad that will have 30" footers -- an inverted flat-bottom bowl, if you will.
Since I'll have a 2x6 sill plate already, would it be practical to lay some treated 2x4's on their sides and use them as floor joists to support a home-shop-built 3/4" tongue-and-groove mahogany floor? This would have the mahogany 1-1/2" above the concrete base, which itself will be a minimum of 6" above grade. My thinking is that such a floor would keep my feet warmer in winter and also provide open space for running electric wires and data cables to the telescope.
TIA!
Davoud
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Davoud asks:

The floor would probably work, with appropriate vapor barrier, but mahogany is awfully soft for a floor. Given a choice, I'd prefer Southern yellow pine.
Incidentally, Honduras mahogany is 800 on the Janka scale while red oak is about 1260 and longleaf yellow pine is about 870.
Charlie Self "It is not strange... to mistake change for progress." Millard Fillmore
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Davoud:

Charlie Self:

Thanks. I'm aware of the softness of mahogany; the ease of working and beauty of mahogany make it my favorite furniture wood. But the observatory will be an *extremely* low traffic area; one person sitting still for hours on end! It's only 78" in diameter.
Thanks again,
Davoud
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First - remember that vapor barrier or suffer the corrosive consequences. Second , depending on your span, you may want additional support for those floor joists. Astronomy and flexible flooring make poor companions. My well shed has 2x6 (full rough) joists over a ten foot span, with 2x elm floor, and I can make it move a bit by bouncing near center.

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George wrote:

Thanks for taking time to reply. Firstly, the eight-sided structure is only 78 inches in diameter (pretending for a moment that it's a circle); secondly, the floor joists would 2x4's lying on the sides and resting directly on the concrete pad; no bounce! The vapor barrier is the big thing.
Thanks again,
Davoud
Davoud asked:

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Suggest you float something on the concrete before putting the wood down to make sure it's absolutely flat. Any movement of the finished floor (due to shifting your weight in the observing chair, for example) will be a nuisance for the telescope view.
Ken Muldrew snipped-for-privacy@ucalgazry.ca (remove all letters after y in the alphabet)
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snipped-for-privacy@ucalgazry.ca (Ken Muldrew) wrote in message

Well, no because the trelescope is not supported by the floor, for that very reason. However that is still agood suggestion to prevent creaking etc. Possibly rooffing felt?
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Ken Muldrew:

Fred the Red Shirt:

*****
Exactly so. The telescope pier will not be connected with the wood floor, or with the concrete pad that supports the wood floor, in any way. It will have a separate concrete foundation (18" dia by four-feet deep) that will be isolated from the observatory floor.
I had squeaky stairs leading to my second floor, and a year or so ago when I was getting new carpet installed I removed the carpet from the stairs myself before the installers came and I put roofing felt under the treads and screwed them down. No more squeaky stairs. (They became squeaky because the wood dried and shrunk during a fire in my house some years ago. The stairs were protected from flame by drywall on the ceiling above the basement stairs, but they were subjected to intense heat.)
Thanks to all who responded. I think I'm going to go for it. The nature and small size of the installation are such that if the mahogany doesn't work out, it will be easily replaceable -- unlike the hardwood floor in a house. And I'll use wide planks so, I can make something else with them if I have to remove them. I often make mahogany boxes as gifts.
Davoud
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Davoud, You can certainly lay 2x4 treated sleepers onto the concrete. However, due to the relatively small space, I would choose to use a synthetic product to resist rot http://www.trex.com /
I would absolutely use a very good vapor barrier in any case. In addition, I would vent it well to provide drying and help reduce humidity variations inside.
As for the Mahogany, given your use, I would lay it onto a heavy 1" or 1-1/8" plywood subfloor first. This will provide a firm, vibration free floor while allowing you to enjoy the look of the beautiful wood.
You might also look at Cambara, very simulair look to Mahogany but harder and very resitant to rot and insects.
PS Very cool scope!
Dave

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