Palomino
member
Reged: 03/08/04
Posts: 26
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Hello all.
Ive read that some people put concrete blocks in the bottom of their footers for their piers so that they dont have to pour as much concrete. I have a 28"x28"x50" footer dug in my backyard and on monday we are going to be pouring the concrete.
Now, I already have enough concrete to do the pour without the blocks my calculations say it will take about 56 60lb bags of quikcrete. Is it just better to pour all concrete in the footer or can the precast concrete blocks be used with no ill effects.
Attached is a pic of the footer hole. It will only come about 4" above grade and then a large steel tapered pier (16" at the bottom tapered to 12" at top) will be attached to 4 5/8" Jbolts coming out of the footer.
Any advice appreciated!
Thanks,
Mike
Athelstane, WI
Edited by Palomino (07/01/08 11:17 PM)
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rsbfoto
super member
Reged: 06/10/06
Posts: 105
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You can use concrete blocks but they are not as heavy as pure poured concrete.
¿ Where is the rebar ? Without rebar you will face the risk that the concrete can crack and then you footer will be just a hand full of artificial rocks :-)
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saludos Rainer
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Palomino
member
Reged: 03/08/04
Posts: 26
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There will be rebar just didnt have it in that pic I took that one just after I finished digging the footer.
So basically the poured concrete only would be better it sounds like?
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Scott K
professor emeritus
Reged: 09/13/07
Posts: 719
Loc: Dallas, TX & Eufaula, OK
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Hi Mike,
I don't really recommend that you do this, for two reasons:
1. Taking shortcuts with your pier is just a bad idea. See the thread entitled "How not to build a pier footer." It's not really applicable to your situation, but it's a cautionary tale, a tale who's moral is - if you have to ask, "hey, will this shortcut for my pier work OK?", you already know the answer. (NO!) All the people who write threads here that seem as if they are overbuilding are getting it right.
2. I have a couple of patios that are kind of pretty, made of rock and cement, over cinder blocks. The cinder blocks are NOT stable, and these patios are crumbling. (They were this way when I bought the house.) Every time I have to mow the patio, I reaffirm my dislike of cinder block!
Best of luck on your pier - what kind of scope will sit atop it? 
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Mel M
member
Reged: 05/04/08
Posts: 12
Loc: southern Oregon
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The concrete is stronger without the block. However, how strong does this need to be? You could probably get by with block and no rebar. I build things with extra strength because I enjoy it.
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Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 1881
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Post deleted by Spoonsize
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Steve Durham
www.margesmonograms.com
(Marge made me do it)
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rodney
domed in NJ
Reged: 03/08/05
Posts: 431
Loc: Asbury, NJ
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Mike,
Some time ago there was a test including cinder (or concrete) blocks. Even though they are not "cinder" they are porous. The result of the test was that originally the concrete appeared to adhere to the block without any issues. However with the blocks in place for weeks the mold was removed and the blocks were no longer firmly attached to the concrete itself. This lead the user to believe that adding the blocks was not a good idea. It was only a short cut. The main problem with this scenario is that once you do or do not pour the concrete into the hole with or without the blocks you are done. There is no way to know if the set up with blocks worked well. If you need I have extra concrete left over and can test this process again and photo document it. It will take me a few days to build a form and set it up. But I am willing to do it for you.
As Scott mentioned. If you are asking about shortcuts you know your answer. You already have all your required concrete for a complete pour. And you are installing the rebar, just make the rebar cage big and strong. You will be fine. My pier is 24 x 24 by 36 deep with the rebar cage. I originally thought about the blocks because I was lazy. I very quickly changed that plan.
Hope this helps some.
Clear skies,
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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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johne
member
Reged: 11/10/06
Posts: 91
Loc: Fort Wayne, IN.
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FWIW...
Many years ago, my father worked in masonry, building block walls. He always told me to make sure that a cinder block was dipped in water just before setting it in place in concrete on the wall. The reason: the cinder block is very dry and porous (as mentioned above) and unless it is 1st dipped in water to pick up moisture, the cinder block will draw/wick a lot of the moisture out of the surronding concrete and weakens the bond with the cinder block.
John
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Celestron CGE-1400
SBIG STL-11000M & ST-402
Takahashi - FSQ106ED F5 Astrograph
Canon EOS 1DsMk2 & 1DMk2 + EF400 f2.8/L/IS
6' Home Dome (Technical Innovations)
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1965healey
Enginurse
Reged: 06/23/07
Posts: 2548
Loc: San Antonio, TX
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One of the things that contributes to the strengh of concrete is the uniformity of each of the different products that make up the mix. It's a recipe just like cake batter or bread dough is. We adjust that recipe depending on the strength we want to achieve, and to a minor extent, on the appearance of the finished product. Rebar and steel mesh are added to provide a rigid structure for the concrete to form around much like what the framing of a house provides for your walls, flooring and roof. It is the consistancy that we use in the choice of materials and their application that provides the strength we need in the finished product. Cutting corners or the use of sub-standard materials usually leads to some sort of performance failure in the finished product. The use of rubble, or TRASH as my Dad liked to call it, to provide fill for a concrete structure is an invitation to problems downstream. If concrete were a clear construction material and you could "see" through it as it settles and then sets up you would be able to view how each of its components works with the others to provide a homogeneous and stable structure. I'd say to stick with proven techniques now to avoid problems in the future. 
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1965Healey (Karen)
Woodlawn Lake Observatory
Celestron CPC 800/FT MIcro/APT Wedge
SV NHNG 80mm #0261/CG5-GT
Losmandy rails/rings
Starizona CWeight system
Celestron Neximage
Sony a100 DSLR/ZigView S2
Meade DS60's w/Autostar (2)
Meade LPI/Meade DSI-C/DSI ProII
750cc Honda Shadow Spirit (Thanks Dad!)
1965 Austin Healey 3000 MKIII
A little too much money and NO SELF CONTROL!
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John Fitzgerald
In Focus
Reged: 01/04/04
Posts: 1029
Loc: AR
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IMO they are just large aggregate. If you fill the holes and the spaces between them it locks them in just like any other aggregate. See the post above from "Spoonsize". I have a refractor pier that is about 56" tall. The concrete part sticks up about 12". It is only about 18" to 20" in diameter in the largest spot and 3 feet into the ground with only three pieces of rebar. The stub the pier is bolted to is 12" in diameter and 12" tall. I poured it from "sackcrecte" mixed in a wheelbarrow, and put j-bolts in the top to bolt the pier flange to. This has been up nearly five years, with no noticeable settling or deterioration. No vibration noticed at over 300x. Not a substantial pier, but works very well. Goes to show that most piers are overbuilt.
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?
Observing since 1966
Messier Cert #898
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Palomino
member
Reged: 03/08/04
Posts: 26
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Hi everyone,
Thanks for the many opinions very interesting discussion. After reading and talking to others Im going to stick with the poured concrete only. I already have enough of the stuff and I bought a mixer pretty cheap to so Im gonna give the back a good work out and do it right
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