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Equipment Discussions >> Observatories

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Footbag
Post Laureate
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Reged: 04/13/09

Loc: Scranton, PA
Concrete questions... Time to panic!
      #5867160 - 05/17/13 01:09 PM

OK. I had a concrete guy scheduled for tomorrow. Long story short, After standing me up 3 times he's not coming. So I have to do the work that he claimed he could do in a couple of hours.

He was going to build the forms for me, but also didn't want to do the pier and base in a single pour. He was going to pour the base and then do the pier a few days later. I was fine with that.

I know a lot of people here suggest a single pour. How do I build the form for a single pour?

It will be 36"x36"x36" with a 12" sonotube rising 60" out of the center. Obviously rebar going through the entire thing, but do I need to plywood the top of the form surrounding the sonotube? I was thinking of just using 2x4's to support and level the sonotube. It will be high up.

Or should I do two pours with such a high sonotube. When my original concrete guy said it wouldn't work, I forgot about it. But a lot of people here seem to do it succesfully.

My picture if it helps.


Edited by Footbag (05/17/13 10:57 PM)


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Alex McConahay
Carpal Tunnel


Reged: 08/11/08

Loc: Moreno Valley, CA
Re: Concrete questions... Time to panic! new [Re: Footbag]
      #5867299 - 05/17/13 02:58 PM

I've helped build something like fifteen observatories. I've seen one pours work, and seen them be disasters.

If the concrete is fairly fluid, there is a lot of pressure pushing up, and it can be very difficult to keep the bottom from forcing its way out of the top of its form. Nevertheless, it can be done by getting the right concrete and building the form right.

I see no difference in strength (or at least no difference that would matter in our application) between a one pour and a two. I would go with whatever your contractor wants to do. After all, he or she is the contractor.

Alex


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rimcrazy
sage


Reged: 03/03/12

Loc: Overgaard, AZ
Re: Concrete questions... Time to panic! new [Re: Alex McConahay]
      #5867340 - 05/17/13 03:19 PM

Your concrete guy is right. My pier was done in two pours. Not a problem at all as long as there is rebar joining one to the other. Depending upon how it is physically made, it is much better. Mine looked similar to yours. I had a square bottom with a round tube poured on top. The square block was poured first with rebar coming out. The second pour filled the round tube. If it was done in one it probably would have been a disaster as the weight of the mix in the tube would have pushed out the bottom. Yours is the same. The right way is to do it in two pours.

FWIW, I actually ended up doing 3 pours. Originally I was going to do a ROR design. I changed it to a dome after the initial pier was complete. With a pier, due to the required height of the new pier, I needed more concrete in the base. I had my contractor dig around the original base, drill in holes and epoxy in rebar and then pour a 1 foot wide by 3 feet deep box around the original base with an additional 6" rebar reinforced on top. Works fine. Nothing loose at all.

Here you can see the original pier with the expanded base around it.



Edited by rimcrazy (05/17/13 03:20 PM)


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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Concrete questions... Time to panic! new [Re: rimcrazy]
      #5867368 - 05/17/13 03:30 PM

OK. Two pours it will be. That will make it a lot easier for me. I'll probably have to mix up the second batch by hand, but 6 bags is better then 88 bags.


I've already cut the wood for the pier form and I had to take tomorrow off work to get everything prepped. This is all stuff my first guy told me he would get done in 2 hours. Well, it took me an hour to cut the wood. Now, I need to build the form, rebar it, drill and rebar the footers, set and level the sonotube footers, then cover it all up with a tarp in case it rains.

I'm letting my anger motivate me. It took me a week to get a hold of this guy and then he strung me along for weeks. I would've had it all done by now.


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Alex McConahay
Carpal Tunnel


Reged: 08/11/08

Loc: Moreno Valley, CA
Re: Concrete questions... Time to panic! new [Re: Footbag]
      #5867401 - 05/17/13 03:40 PM

After you have hammered the wooden form together, wrap it in nylon or wire strapping--real tight.....

Alex


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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Concrete questions... Time to panic! new [Re: Alex McConahay]
      #5867427 - 05/17/13 03:46 PM

Quote:

After you have hammered the wooden form together, wrap it in nylon or wire strapping--real tight.....

Alex




I thought I was crazy for dreaming this up, but I have a rope swing rope that I was planning on wrapping around it. I guess it's not as crazy as I thought.

BTW.... Alex, thanks for the PDF guide on the Lodestar RJ-12 cable. I made a few and am in the process of testing them out. Great info!


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astrodog73
super member


Reged: 02/22/13

Loc: Australia
Re: Concrete questions... Time to panic! new [Re: Footbag]
      #5867864 - 05/17/13 06:05 PM

I did mine in two pours, but just a couple of hours apart, just enough time for the base to firm up, then put the form on, reinforcing protruding from base, then poured the pier....

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mattw
sage


Reged: 07/19/06

Loc: Arkansas
Re: Concrete questions... Time to panic! new [Re: astrodog73]
      #5868064 - 05/17/13 08:09 PM

I posted my observatory progress awhile back and
was rebuked for a so-called "capped" pour, but mine
has worked just fine, and with a fairly large payload.
And I built a really tight, heavy wood frame for the 2nd pour.


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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Concrete questions... Time to panic! new [Re: mattw]
      #5868243 - 05/17/13 09:58 PM

OK. My form is built. I need to pickup more rebar tomorrow. Lots of stuff to do, but I think it will go quickly.

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zerro1
Postmaster
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Reged: 08/02/09

Loc: Smokey Point , 48.12°N 122.25...
Re: Concrete questions... Time to panic! new [Re: mattw]
      #5868310 - 05/17/13 10:26 PM

the whole thing with two pours is that you get what is called a cold joint. It's only a problem if you don't carry the connection with re-bar. structurally (in a perfect world) you want two feet of r-bar overlap to tie in the second stage. So you can either install the entire r-bar cage in the first pour, allowing the verticle bar for the pier to stand out of the base. then just stand the sono tube over the protruding cage, stabilize it so it can't move and do the second (pier) pour. Or leave two feet of bar protruding from the base to tie in the pier r-bar cage. either way is industry acceptable.

A guy can get pretty carried away with re-bar cages. You could have 4, 5, or 6 "or?" verticle bar inside the somo tube, you can add rings to that. how about some 18" J-bolts tied in to the R-bar for your attachments.

I work for a GC in comercial construction. Mostly we hire it done but many times we do it ourselves. Can't tell you how many light pole(24"diam X 6'tall) bases I've setup and poured.


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JJK
Carpal Tunnel


Reged: 04/28/08

Re: Concrete questions... Time to panic! new [Re: zerro1]
      #5870840 - 05/19/13 07:55 AM

Quote:

SNIP
I work for a GC in comercial construction. Mostly we hire it done but many times we do it ourselves. Can't tell you how many light pole(24"diam X 6'tall) bases I've setup and poured.




Man, everything is treated as top secret nowadays. ~\8^)


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thesungazer
Sungazer
*****

Reged: 05/06/03

Loc: Maryland
Re: Concrete questions... Time to panic! new [Re: JJK]
      #5870888 - 05/19/13 08:44 AM

Do your back a favor too and rent a concrete mixer. Even for 6 bags.

Best of luck. You'll love it.

Greg


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zerro1
Postmaster
*****

Reged: 08/02/09

Loc: Smokey Point , 48.12°N 122.25...
Re: Concrete questions... Time to panic! new [Re: JJK]
      #5872002 - 05/19/13 05:15 PM

Quote:

Quote:

SNIP
I work for a GC in comercial construction. Mostly we hire it done but many times we do it ourselves. Can't tell you how many light pole(24"diam X 6'tall) bases I've setup and poured.




Man, everything is treated as top secret nowadays. ~\8^)




It's not a secret I've just lost count over the years


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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Concrete questions... Time to panic! new [Re: zerro1]
      #5875279 - 05/21/13 08:04 AM

OK. I'm not longer panicking. I have a new concrete guy coming tomorrow. t will be done in two pours. I'll do the second pour for the pier.

I won't be able to prevent the cold joint, but I have three pieces of rebar coming through. I can add more if I need.

Is there a time limit on how quickly I should make the second pour? I'm considering doing some framing before the pier. That should help me reach it with the concrete. Otherwise it could be a bit hairy.


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rimcrazy
sage


Reged: 03/03/12

Loc: Overgaard, AZ
Re: Concrete questions... Time to panic! new [Re: Footbag]
      #5876166 - 05/21/13 03:15 PM

My two were done within 48 hours but after 24 it could have been 2 weeks and the results were the same. You just need rebar between the two that is all.

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hottr6
Carpal Tunnel
*****

Reged: 06/28/09

Loc: 7,500', Magdalena Mtns, NM
Re: Concrete questions... Time to panic! new [Re: rimcrazy]
      #5876585 - 05/21/13 06:19 PM

I'm coming into this thread very late, and my reading indicates that most people believe that the pier and the floor, whether one pour or two, should be "connected", either through a cold joint or rebar or both or whatever. Am I interpreting this correctly?

I ask this question because if 'twere me, I would isolate the pier from the floor. Put a 1" gap between the two pours, and when cured, fill the gap with something elastic like closed-cell foam.

If the pier and base are connected, any vibration in the floor will communicate with the pier. Any slumping of the floor will torque the pier.


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Alex McConahay
Carpal Tunnel


Reged: 08/11/08

Loc: Moreno Valley, CA
Re: Concrete questions... Time to panic! new [Re: hottr6]
      #5876667 - 05/21/13 06:43 PM

I am pretty sure we all agree with you. The pier should be isolated from the floor.

O think Footbag's questions all relate to whether it is okay to have one pour or two. (That is, form the base of the pier, and then come back some time later and pour the top three to five or so feet of the pier.) The advice of this thread is that it is okay to pour in two pours as long as they are connected with rebar.

But, yes, when it comes time to pour the slab for the floor, it is important to put the insulation around the pier so that vibration does not transfer one to the other.

Alex


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Footbag
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Reged: 04/13/09

Loc: Scranton, PA
Re: Concrete questions... Time to panic! new [Re: Alex McConahay]
      #5876690 - 05/21/13 06:52 PM

I will not have a concrete floor. It's footers for what will become a supported wood floor. It will all be completely isolated from the pier. Which will be poured in two pours. The base and the actual pier which rises 56" off the base.

But yes. Piers should always be isolated from the floor as far as I've read.


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zerro1
Postmaster
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Reged: 08/02/09

Loc: Smokey Point , 48.12°N 122.25...
Re: Concrete questions... Time to panic! new [Re: Footbag]
      #5876829 - 05/21/13 07:58 PM

It does not matter how long you wait between pours. With the Re-bar present, I wouldn't fret over it but you could throw a little moose milk around the area where the base of the pier meets the foundation/footing. Just give the last pour a fair amount of time to really cure before you pile the gear on top. (a few days)

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MRNUTTY
Carpal Tunnel
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Reged: 11/22/11

Loc: Mendon, MA
Re: Concrete questions... Time to panic! new [Re: rimcrazy]
      #5876864 - 05/21/13 08:21 PM

@rimcrazy, cool pier! What are you packing on top?

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