on the Wine Cellar Project
Colorado, July 2001
The completed cellar is 24 ft wide X 40 ft long. A central beam (8" wide X 16" high) runs down the 40ft length and is supported every 10ft with 8" round pillars. This gives the whole business a McDonald arch shape. False arches were formed between the interior pillars to jazz up the inside.
Formwork: Inside and underneath, we used 2 movable forms to pour 10 linear ft at a time. Arched trusses were formed from 1/2" and 3/8" rebar and placed 2ft on center. On top of this 1/8" masonite. Four men could lower and move the forms and set them up ready to pour the next section in 2 1/2 hrs. This worked out very well. On top of the masonite went 6 mil plastic, chicken wire (to keep the light weight in place), and 1" light weight concrete (expanded shale and vemiculite). This stiffened everything up. Then the mesh, 2 layers of #6666WW, separated by 3/4" tiaqngular, ladder shaped spacers-- called slab bolsters. The mesh rolled out nicely and was perfectly spaced for the 2 1/2" pour. Between the mesh and 3 ft on center went, horizontal, 1/2" rebar that bent up at 60 deg., then at 90 deg. to follow the form of the vertical ribs. I had these pieces bent up at the local rebar supply and they greatly simplfied forming the ribs. The ribs are standing, 10" high, triangular shaped and 5 ft. on center. I'd make 8" ribs next time or forget about them entirely unless building in earthquake country.
The Pours: We poured the columns, beam, and first vault from a single redi-mix truck. This was a mistake as it was difficult to fill columns with the 7 sack, 3/8" chip, 2" slump. Vibrating hell and a minor blowout. After doing calculations we decided it would cost us about the same and be a lot less hectic to mix and pour by hand. So we built a skywalk out of planks and mixed on the edge of the excavation to pour the last 3 vault sections.The lowest 5ft of the vault is almost vertical so we poured it first thing in the morning in 3 each, 2ft lifts (1/2" plywood) [see photos], then started dumping and raking off the top. We vibrated everything, most stuff twice with a 2hp pencil vibrator. Ideally I'd use a different vibrator for the membrane sections. We stripped the lower forms after 2hrs (it was over 100 degs outside for most of the job). In the afternoon we polished with 3/8" thick, sand and cement. One side of the vault one day (10 ft), one side the next. Five day cure and move the forms. Bagged and misted for 2 weeks. Filling the ribs was a challenge and we tried a bunch of different ideas but I still haven't hit on THE GREAT IDEA for this step. Making them smaller would help without compromising much strength -- IMHO.
All of the above is only one way to get the job done with light weight formwork and no access to a pump. It worked but it was a hell of a lot of work. Good for do-it-yourself (take 6 months -- no problem), third world, and folks not into borrowing money--pour two sections htis year, seal ends with strawbales , move in, next year pour two more sections, etc.
The inside, we plastered with Nolan's stucco sprayers, 3/8"(one coat) to 1" (2 or 3 sprays) thick. Fixing irregularities was fairly easy, what with the 1" lt wt layer. Sponge finish. Half white and half grey portland for the finished lite grey color. It won't be painted or sealed on the inside which is an idea I like a lot. One of my goals from the start, which I didn't acomplish, was to not leave a shinny surface on the inside.Plaster doesn't want to stick. Even with neat cement and bonding agent painted immediately before spraying, I worry about pieces peeling off , 2-10 years down the road.
Next time I'd join the different pours,out, on the "membrane" sections, rather than trying to join at the ribs--easier to see what you are doing and according to feedback, the center of the membranes is less critical structurally.
Backfilling was done carefully with a small 4WD tractor loader, which drove on top without problem.