skybsd
sage
Reged: 02/01/08
Posts: 219
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Hi,
I guess this is a question to those that have used sonotube (or similar solutions) in building their concrete based piers...,
To start off.., I know nothing about concrete and construction in general - and my building skills are "self-hazardous" at best 
However, in planning my concrete pier, a couple of things I'm struggling with in reading other people's notes on the construction of their concrete piers concern me, and I'd appreciate some clarification from you guys that have poured your own piers, please..,
The "givens":
a] Sonotube length = 5ft
b] Hole = 2ft x 2ft x 2ft
c] Rebar = 4 rods
Questions: -
1] Is the sonotube placed straight down, to the bottom of the hole - so that the base is flush with the bottom surface of the hole?
I'd have thought not, but maybe you know something I don't?
2] Sonotube (and others) have the outer lining skin that you peel off after the concrete is set. Given that you can only then peel off what is visible above ground, are there any concerns about the remaining skin that is still below ground?
3] Regardless of [1].., because there IS the outer skin that remains in place below ground, the concrete that been poured inside of the tube does not (all) meet, nor bind to the concrete on the outside of the tube.
Doesn't the resulting pier end up being a (mostly) separate (granted made of concrete) pole that's slotted into a "concrete block with a hole in the middle"?
As I said, knowing nothing about this stuff, I accept the fact that there's some glaringly obvious point that I've missed in all the posts that I've read. Please fill in the blanks 
Thanks, guys / gals!
Regards,
skybsd
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Galaxyhunter
scholastic sledgehammer
Reged: 01/02/06
Posts: 827
Loc: Northern Illinois
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Quote:
1] Is the sonotube placed straight down, to the bottom of the hole - so that the base is flush with the bottom surface of the hole?
NO it does not. There are a couple of ways to do this. a) Do it in two pours, The 2x2x2 base first with the rebar in location up into where the sonotube will be placed,after that has setup, then put you sonotube down to the concrete you just poured & pour the tube. b) make a plywood or a OSB top that will cover the 2x2x2 hole that has a hole for the sonotube. Mount the sonotube on that cover so the tube is flush with the bottom of the cover. Place the cover over the hole & stake in down. Brace the sonotube so it is vertical. Then pour it all at once though the top of the sonotube.
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Carl
Hawkeye Observatory
Observatory - "Hawkeye"
Scope - 18"f4.5 on a GEM
8" f4.9 Orion piggy backed
Drive - Sitech Technology
DSC - Sky Commander
Planetarium - MegaStar
Camera - ST2000XM
Desire - comes & goes
Talent - ZERO, NONE, NADA (But I can Wish)
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okiestarman56
super member
Reged: 04/10/08
Posts: 158
Loc: 36.9'33" N 95.23'29" W
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The rebar in the base should have small 90 degree bends and keyed some way if you do a two stage pour(to prevent a cold joint) From 30 years of pouring mud, soil can move two seperat piecs of concret even with rebar. Jerry
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305mm f/5 DSO 12" GSO
114mm f/7.8 Tasco 4.5" Red Tube
80mm f/15 Sears 3.1" Refractor
60mm f/15 Sears 2.3" Refractor
Plenty? of EP's .965 to 2"
2 LPI's
Home made Denver chair
3-7'x10' light panels
yada yada yada
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skybsd
sage
Reged: 02/01/08
Posts: 219
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Hi,
Good to hear from you guys..,
With the two-pour method, is the second pour done before the first one has set?
Not doubting your suggestion, but somehow I've got it in mind that a single-poured pier would be more stable.
I'm simply going by the the fact that concrete isn't super-glue like it the second pour being able to adhere to the first one.
I am therefore, tending towards option (b)..,
Thanks again for the responses! Keep 'em coming, okay?
Regards,
skybsd
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rodney
domed in NJ
Reged: 03/08/05
Posts: 428
Loc: Asbury, NJ
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I think what Carl is saying is you pour your base, let it start to set up and then insert your sonotube while the base is still fluid. Thus the braces he comments on to support the tube in the desired position are added. A two part pour will work as long as the base has not set.
Clear skies,
--------------------
My Explora Dome construction is here:
http://www.freewebs.com/rodbo1967/observatoryconstruction.htm
Rodney
13 Truss
C8-NGT
Orion 80mm/F11
Extremely happy owner of an Explora Dome home observatory
and a list of goodies to big for this sig
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skybsd
sage
Reged: 02/01/08
Posts: 219
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Hello,
So regardless of which (one / two pour) method used, the base of the sonotube is somewhat above the base of the hole - agreed.
Let's say then that I had catered for 2ft of sonotube being below ground, leaving 3ft as exposed pier. I figured 2 out of the 5ft being used as "foundation" is enough for stability, you see.
How high off the bottom of the 2ft deep hole can I have the sonotube then?
Or should I go deeper (say to 3ft) so that there's 1 foot's worth of concrete below the base of the tube in order to maintain my sunken 2ft stability + 3ft above ground pier?
Thanks again - I hope I'm making sense!
Regards,
skybsd
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guyinthesky
sage
Reged: 04/13/07
Posts: 330
Loc: western ma.
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keep in mind the farther in the tube is, the more cardboard there is between the joint. i put mine in so only 2 inches of tube was below the concrete line. i poured the base, then 2 hours later the tube. if you pour it all at once, you risk the hydraulic action of the weight of the concrete in the tube squeezing out the bottom. john
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Zhumell 12" dob
celestron c100ed-r gt cg-5
meade 5" telestar reflector
just enuf naglers
astro-tech 66ed
celestron C9 1/4
oberwerk 100-45
ALVAN CLARK and SONS 3 inch refractor
canon 350d
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Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 1858
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DO NOT pour this pier with any of the sonotube below the top level of the pier base. When ALL the concrete is set up you will have the ability to strip off ALL the sonotube. Wheter you do or not makes no difference, but you will have the ability.
If you dig a two foot deep hole, the bottom of the sonotube ought to be two feet from the bottom of the hole.
The pier base must be larger than the sonotube for stability. I suggests at least 2 feet square and 2 feet deep with 36 inches of sonotube on top of that. Use a hand saw to cut the sonotube off.
--------------------
Steve Durham
www.margesmonograms.com
(Marge made me do it)
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skybsd
sage
Reged: 02/01/08
Posts: 219
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Hi Spoonsize,
Quote:
DO NOT pour this pier with any of the sonotube below the top level of the pier base. When ALL the concrete is set up you will have the ability to strip off ALL the sonotube. Wheter you do or not makes no difference, but you will have the ability.
Okay, I see - Is this what you mean?
Quote:
If you dig a two foot deep hole, the bottom of the sonotube ought to be two feet from the bottom of the hole.
The pier base must be larger than the sonotube for stability. I suggests at least 2 feet square and 2 feet deep with 36 inches of sonotube on top of that. Use a hand saw to cut the sonotube off.
I think I understand. I had been researching sites where others have documented their pier builds like this one where the sonotube appears to have been simply placed into the hole and concrete then shoveled into everything somehow.
Not necessarily fingering all that have done this, but by what you (and others) have said here, I might have been fortunate in having these concerns anyways.,
Thanks again. Will set about rethinking my plans again.
Cheers!
Regards,
skybsd
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Pedestal
Carpal Tunnel
Reged: 03/11/06
Posts: 2830
Loc: Smoggy Bottom, Baytown,Texas
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There are several ways to skin this cat, and a lot depends on what you want to wind up with in the end.
First, think of a 2 part pour as a single, extended pour. You pour your base, then you setup your sonotube, fastening it securely in place, level and square, with the bottom where it meets your base concrete well caulked. Your rebar should be in the base part and extend up inside the sonotube. (how many, how big, is not that important) As the base begins to set, it will reach a point where it seems pretty solid, but is easy to scratch. At that point, you pour the pier, vibrating (tap with a hammer) all the way up. Don't wait until the sonotube is full to start the vibration process.
Do you want the base to be level with the ground? Or do you want the base to extend up perhaps to the level of a deck above ground? In EITHER case, you are going to have to build some kind of structure around the base hole to secure the sonotube.
Keep in mind, the easiest way to ruin concrete is to use too much water. Follow the mixing directions on the bag. It also does not hurt to buy an extra bag or two of concrete (not Readymix) and add a shovelfull to each bag as you mix it.
Just some thoughts you might find helpful.
Hubert
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www.smoggybottom.org
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Galaxyhunter
scholastic sledgehammer
Reged: 01/02/06
Posts: 827
Loc: Northern Illinois
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Take a look at the four 12" sonotubes on the back side of the main slab. It is hard to see from this angle, but I fastened them to a small sheet of 3/4" OSB. I placed the OBS / sonotube assembly over the hole I bored into the ground. I used about 8 tent stakes to holed each piece down. Then I poured through the top of the tubes. Each of the holes were bored 4' down & poured about 2' up into the tubes. The soupier you make the mix, the more chance of a leak where the OSB meets the ground.
http://www.hawkeye-observatory.com/misc/Pillers.jpg
--------------------
Carl
Hawkeye Observatory
Observatory - "Hawkeye"
Scope - 18"f4.5 on a GEM
8" f4.9 Orion piggy backed
Drive - Sitech Technology
DSC - Sky Commander
Planetarium - MegaStar
Camera - ST2000XM
Desire - comes & goes
Talent - ZERO, NONE, NADA (But I can Wish)
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marc4darkskies
newbie
Reged: 01/17/08
Posts: 1
Loc: Sydney, Australia
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Here's my experience: Observatory Construction
As you'll see I used the 2 pour method. It's pretty easy as long as you prepare properly.
I was a complete building novice too before I started but thankfully I had an astro-buddy to advise me. Now I at least know what wet concrete feels like! 
Good luck!
Cheers, Marcus
--------------------
He who dies with the most toys wins!" "
My stuff: Tak TOA-150 :: Tak EM-400 Temma II :: SBIG STL-11000M + AO-L :: Sirus Observatory
My Picture Site
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skybsd
sage
Reged: 02/01/08
Posts: 219
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Hi Pedestal,
Good to hear from you..,
Quote:
There are several ways to skin this cat, and a lot depends on what you want to wind up with in the end.
Oh that's the easy bit.
What I am after is a rock-solid concrete pier that rises up to a minimum of 3ft off the surface of the ground. During installation, I'll also be setting up the pier adapter fixings for my mount.
I've got a 5ft x 10in length of sonotube for the job.
That's it
Quote:
First, think of a 2 part pour as a single, extended pour. You pour your base, then you setup your sonotube, fastening it securely in place, level and square, with the bottom where it meets your base concrete well caulked.
Okay.., so this "caulking" stuff is a new step. So that reads like: -
1] Dig hole 2'x2'x2'
2] Fill hole with concrete
3] Place 3' sonotube over hole, secured, leveled and square
4] Seal around the base of the sonotube where it meets the top surface of the already pured concrete in the hole
Quote:
Do you want the base to be level with the ground? Or do you want the base to extend up perhaps to the level of a deck above ground? In EITHER case, you are going to have to build some kind of structure around the base hole to secure the sonotube.
What I had in mind is to simply have the concrete pier "rise up" from the ground, to be honest. I figured on needing to have the sonotube "held in place" by a bracketing framework all around during the pour and afterwards for time needed for the concrete to set.
Thanks for all the help!
Regards,
skybsd
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Pedestal
Carpal Tunnel
Reged: 03/11/06
Posts: 2830
Loc: Smoggy Bottom, Baytown,Texas
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Consider a wooden "tripod" affair to secure your sonotube, with the legs extending outside of your hole. Also, consider digging your hole a few inches deeper, and don't pour your concrete all the way to the top. After the temporary stuff is out of the way, put some topsoil over the "chunk", and voila! A pier rising out of the ground...
And that ground is certainly a bit softer than that concrete chunk when you drop that eyepiece. 
The caulk around the bottom of the sonotube is probably not necessary. However, it doesn't cost much, and worth the "peace of mind".
Hubert
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www.smoggybottom.org
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skybsd
sage
Reged: 02/01/08
Posts: 219
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Hi Rodney,
Quote:
I think what Carl is saying is you pour your base, let it start to set up and then insert your sonotube while the base is still fluid. Thus the braces he comments on to support the tube in the desired position are added. A two part pour will work as long as the base has not set.
Clear skies,
I had a look at the observatory construction pages at the site in your signature. Can I ask about how you poured your pier, please?
See - what I wish to have is similar to what you have - except that instead of mounting a top metal pier, I want to have an all-concrete pier.
Thanks.
Regards,
skybsd
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MikeV
member
Reged: 11/17/05
Posts: 23
Loc: Long Island, NY
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skybsd,
I did mine in a single pour using a plastic footer form. You can read more about them here -> http://www.bigfootsystems.com/ While it made for digging a bigger hole, I was able to install, level and backfill before I did the pour. I have construction pictures posted on my website: www.graystarobservatory.com
Regards,
Mike V.
--------------------
12" Meade RCX400
SkyShed POD
NexStar 5
Orion ST80
Coronado SolarMax 40
Meade DSI-C/DSI ProII
"The heavens declare the glory of God; the skies proclaim the work of his hands."
Psalm 19:1
Graystar Observatory
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skybsd
sage
Reged: 02/01/08
Posts: 219
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Hi Mike,
Good to hear from you..,
Quote:
skybsd,
I did mine in a single pour using a plastic footer form. You can read more about them here -> http://www.bigfootsystems.com/ While it made for digging a bigger hole, I was able to install, level and backfill before I did the pour. I have construction pictures posted on my website: www.graystarobservatory.com
Thanks for the links. I need to clarify a couple of things though..,
What exactly do you mean by "back-filling"? Looks to me that you: -
Dug the hole
Installed and leveled the Bigfoot footer
"Backfilled" the footer????
Secured the tube to the footer
Poured the concrete into the tube
Left the concrete in tube to set
So..,
What's that backfilling all about?
Is the hole you dug the same diameter of the tube?
Thanks.
Regards,
skybsd
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 11505
Loc: Rockford Illinois
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Back filling is quite literally putting the dirt BACK into the hole.
You have to also understand what it is he's using. Check out this link:
http://www.bigfootsystems.com/
The hole he dug is MUCH wider than the tube. Must be bigger to accommodate the bigfoot.
--------------------
Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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skybsd
sage
Reged: 02/01/08
Posts: 219
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Hello,
Quote:
Back filling is quite literally putting the dirt BACK into the hole.
Yes, this is what I suspected, but had trouble rationalising, to be honest. In the reading I've done, many suggest that this isn't really ideal from a stability point of view. But I was catering for the fact that "backfilling" may have some other meaning, given that I openly do not know anything about construction
Regards,
skybsd
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 11505
Loc: Rockford Illinois
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Quote:
Hello,
Quote:
Back filling is quite literally putting the dirt BACK into the hole.
Yes, this is what I suspected, but had trouble rationalising, to be honest. In the reading I've done, many suggest that this isn't really ideal from a stability point of view.
I'm in full agreement with you on this one... Undisturbed soil is always best.
--------------------
Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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