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.
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.
"It is not strange... to mistake change for progress." Millard Fillmore
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.
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.
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.
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.
(remove all letters after y in the alphabet)
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
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
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
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!
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