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#1 StarmanDan

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Posted 28 January 2013 - 04:14 PM

Looking for advice on building a cinder block pier. I have an elevated garden that is no longer used that was made with cinder blocks. I'm considering using some of these to build a pier. I've already got about a 2x2x2 foot hole dug to use as the footer. I estimate the pier will need to be about 5' tall for my pier and beam observatory. A few questions:

I assume I'll need to let the footer completely set before I build the pier? Do I need to tie the footer and pier together with rebar? Should I fill the voids in the blocks after I've got the pier to the preferred height or can I fill them as I go? What is the best way to ensure that the cinder blocks remain level and plumb as I go?

#2 berlinstar

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Posted 28 January 2013 - 04:55 PM

You can get sonotube really cheap, so why not just go the round route? Plus, cost will be somewhat of a factor because youll need to put rebar in the blocks, then pour them solid, unless they're already solid. The last thing you would want is your scope falling due to a bad mortar joint after a couple of years.

Lastly, as rough and abrasive as blocks are, I IMHO youd be better off with something round or contoured (again, the sonotube).

#3 StarmanDan

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Posted 28 January 2013 - 05:22 PM

I've looked at sonotube and the longest length I can find is 4'. I would need at least 5' or a little more for my obs design. The cost of rebar is not a factor as I would have used rebar for the sonotube too. If I fill the voids in one go, I would essentially accomplish the same goal as using sonotube so I shouldn't have to worry about a bad mortar joint failing.

#4 jazle

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Posted 28 January 2013 - 05:30 PM

Go to your local construction supply shop. I see you're in Texas and I see Whit Cap has locations throughout the state. They have sonotube in all sizes and will cut whatever length you need right there. I bought a 6' section of 18" tube recently for about $40:
https://www.whitecap...ucts/128CF18SRG

#5 mclewis1

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Posted 28 January 2013 - 06:13 PM

I did a cinder block pier support that's about 8' in height (5' below grade, 3' above). The first course of blocks was laid on undisturbed earth and the blocks were oriented to spread out the weight. The rest were just stacked in alternating positions.

I put rebar down through the 4 holes and filled it with concrete as it was built up. The top had J bolts added.

The concrete between the blocks was also used as mortar between each section which allowed some play in ensuring the support was as close to vertical as possible/practical. My steel pier allows for leveling the top plate so I didn't worry about the pier support being absolutely level.

After 18 months of use I don't think I've seen more than 1/8" of movement from vertical. I've been very impressed by just how solid this concrete filled cinder block pier support has been.

It was quite easy to build, with no need to build any form of support that a sonotube type of setup would have required.

Posted Image Posted Image Posted Image

#6 Gastrol

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Posted 28 January 2013 - 06:26 PM

I would use a sonotube but if you want cinder blocks you can dry stack them starting from the bottom of the dug out footer up to the desired finished height. Use bond beams (cinder blocks with cutouts on both ends) within the footer to allow the concrete pour to be monolithic. Install horizontal rebars through the bond beam blocks within the footer in addition to the vertical rebars running the entire length of the pier.
Pour concrete into the footer and from the top of the pier into the voids .

#7 StarmanDan

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Posted 28 January 2013 - 10:28 PM

Jason, Thanks for the link but the closest White Cap is a two hour drive from me.

Mark, That's one serious pier! Did you dry fit the blocks below grade then mortared the blocks above grade?

I may do cinder blocks to get me up to a level where I can use the 4' sonotube.

#8 Alex McConahay

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Posted 29 January 2013 - 12:33 AM

2 x 2 x 2 is pretty substantial, but it is actually a bit shallow. Try to get it deeper. This is especially true if you have frost problems.

Alex

#9 roscoe

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Posted 29 January 2013 - 06:58 AM

Dan,

Yes, you'd want to let the concrete in the base set up first. Deeper won't hurt anything, and if you pour it right into the hole (no forms) it'll be very stable when it sets up.
If you put 2 - or 4 - rebars in it, sticking up some, that'll tie the blocks in. As you build up the blocks, you can add rebar in pieces, so you don't have to lower the blocks down several feet of rebar, and you can mortar them together as you go, using a short level to check each course, to keep things straight. put a bit more mortar than needed in the joints, and tap them down with a hammer to the right height, When you fill the voids, fill them 1/2-2/3 full each time, so any weak spot between fills happens in, not between, the blocks, particularly at lunch or the end of a day.
You could fill the voids every course, or every 3 or 4, whichever seems to make more sense....Consider installing a piece or two of plastic conduit, so you will have a way if desired to bring power or computer lines up to the scope.

I've always favored block piers, because the amount of site-mixed concrete is much less, the amount of effort needed to set up and brace the sonotube form is not an issue, and the need to lift lots of wet concrete several feet into the air to pour it down a tube is also not there.

Since you already have blocks on site, your cost for the pier will be small, but someone starting out could also investigate the local availability of square blocks called chimney blocks or fireclay chimney liners called flue tiles, which are round or rectangular smooth-sided tubes about 2' tall - sort of like permanent sonotubes - but nicer. Bricks and mortar also make a beautiful pier that can be built up a bit at a time as time and energy allow.

These supplies are usually found at masonry supply houses, not the local big-box.....

Russ

#10 nytecam

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Posted 29 January 2013 - 09:11 AM

Posted Image

Looking for advice on building a cinder block pier. I have an elevated garden that is no longer used that was made with cinder blocks. I'm considering using some of these to build a pier. I've already got about a 2x2x2 foot hole dug to use as the footer. I estimate the pier will need to be about 5' tall for my pier and beam observatory. A few questions: I assume I'll need to let the footer completely set before I build the pier? Do I need to tie the footer and pier together with rebar? Should I fill the voids in the blocks after I've got the pier to the preferred height or can I fill them as I go? What is the best way to ensure that the cinder blocks remain level and plumb as I go?

To state the obvious blocks or bricks are designed to be manageable by hand so piers so built block at a time are good - the void in the middle should include galv wall-ties built in as you go so when the void is filled with concrete, all is locked together. My blockwork pier pic above is capped with concrete within the obsy to receive a steel column and inclined equatorial wedge for scope - saves on expensive wedge Check out my DIY obsy via link below :grin:



#11 mclewis1

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Posted 29 January 2013 - 10:48 AM

Mark, That's one serious pier! Did you dry fit the blocks below grade then mortared the blocks above grade?

Dan,

It's "mortared" all the way down, this allowed for the ability to true up the pier support as we went (checking with a level and a few hammer taps).

The benefits of this type of construction for me were a) no forms/bracing B) less concrete mixed/used c) wider base for my steel pier (a 12" Sonotube wasn't going to be wide enough) and d) built with very easy techniques.

The downside to using the cinder block technique was that I needed a larger hole to work in, this wasn't a real problem for me since I had to remove a huge tree stump first (so the tools were in place and we just made the hole a bit deeper). In hindsight I figure I could have worked in a smaller hole with the cinder blocks but it would have been tricky. With a Sonotube setup I might have been able to pour a rough footer with a smaller diameter hole. Dig a 5' deep hole, line the bottom with a little crushed rock, pour concrete into base of hole, add Sonotube and rebar it into the "footer" while it was still wet, then align and reinforce/brace the Sonotube and continue the pour.

My pier support is supporting a 200lb steel pier and another 200lbs of equipment (mount/scopes/counterweights). I planned the cinder block support to handle at least 500lbs on top of it.

#12 nytecam

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Posted 29 January 2013 - 10:58 AM

[quote name="mclewis1"]....Dig a 5' deep hole, line the bottom with a little crushed rock....[quote] Mark - as an architect I find this a common DIY mistake in UK - the bottom of a freshly dug hole is virgin ground and undisturbed for decades or longer and as compact as it can get and receives the founds concrete pore direct :o Perhaps things are different Stateside :p

#13 StarmanDan

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Posted 29 January 2013 - 03:45 PM

2 x 2 x 2 is pretty substantial, but it is actually a bit shallow. Try to get it deeper. This is especially true if you have frost problems.

Alex


Being in the south, my frost line is only a few inches down. I wish I could go deeper, but my whole yard is limestone aggregate and I think I've hit bedrock as it is.

Russ, thanks for the concise and detailed instructions! This gives me much more confidence over using the sonotube.

My main concern with sonotube is making sure it remains plumb and level over the course of filling and setting. I've heard horror stories of concrete blowing out the bottom or the tube slowly leaning as the concrete sets. Since my yard is mostly rock, I haven't devised a way to stake the tube down to ensure this doesn't happen.

Additionally, my time will be limited to working on this project for a few hours a week, so it's desirable to have the ability to build the pier in stages, as I have the time, which it seems the block approach provides.

#14 mclewis1

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Posted 29 January 2013 - 04:08 PM

....Dig a 5' deep hole, line the bottom with a little crushed rock....

Mark - as an architect I find this a common DIY mistake in UK - the bottom of a freshly dug hole is virgin ground and undisturbed for decades or longer and as compact as it can get and receives the founds concrete pore direct :o Perhaps things are different Stateside :p

Maurice,

You are absolutely correct, I should be clearer on that point. More than just a single layer of loosely distributed crushed rock would be a big mistake. I use the rock to keep the concrete from spreading out too much but I always ensure the concrete gets down to that important undisturbed earth layer.

Don't know about "Stateside" but that's how most folks do it here in Canada ;)

#15 Mary B

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Posted 29 January 2013 - 07:28 PM

Drill the bedrock and epoxy in rebar to keep the pier upright, also build a frame cage around it.

2 x 2 x 2 is pretty substantial, but it is actually a bit shallow. Try to get it deeper. This is especially true if you have frost problems.

Alex


Being in the south, my frost line is only a few inches down. I wish I could go deeper, but my whole yard is limestone aggregate and I think I've hit bedrock as it is.

Russ, thanks for the concise and detailed instructions! This gives me much more confidence over using the sonotube.

My main concern with sonotube is making sure it remains plumb and level over the course of filling and setting. I've heard horror stories of concrete blowing out the bottom or the tube slowly leaning as the concrete sets. Since my yard is mostly rock, I haven't devised a way to stake the tube down to ensure this doesn't happen.

Additionally, my time will be limited to working on this project for a few hours a week, so it's desirable to have the ability to build the pier in stages, as I have the time, which it seems the block approach provides.



#16 Gastrol

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Posted 29 January 2013 - 08:30 PM

My main concern with sonotube is making sure it remains plumb and level over the course of filling and setting.


I poured my 4' sonotube without any braces to hold it plumb. I only braced the tube with 2x4's near the bottom to keep it suspended just about an inch or so below the top surface of the footing. I kept it true and plumb as I poured along, footing and pier in one session. I made small adjustsments as I went along, no problem. The tube also remained perfectly plumb as the concrete set.
I can understand securing plumb a longer length of sonotube but for a tube only 4' in length you can do without.

I've poured several sonotubes without braces for other projects prior to building my obs so I was comfortable with my no bracing method.

#17 roscoe

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Posted 29 January 2013 - 11:23 PM

A rebar comment - most astronomers put a lot more rebar than is needed their piers...... I'm a carpenter, have installed a lot of posts and piers for decks and sheds and the like, and have had to remove quite a few, also.
A pier with no rebar can be fairly easily broken off by bumping it with a backhoe bucket, a pier with even one piece of rebar cannot be broken off, and has to be dug out whole. A regular post installation around here uses one vertical piece of rebar with the bottom bent into a hook, with one or two short pieces set in the hook sideways or crossed, with a j-bolt tied onto the top end with fence wire. Often smaller piers get only a vertical piece with the bottom bent some......
I've dug 50-year-old piers out built this way that, if the concrete was mixed right, were good as new.
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#18 *skyguy*

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Posted 30 January 2013 - 09:22 PM

Should I fill the voids in the blocks after I've got the pier to the preferred height or can I fill them as I go? What is the best way to ensure that the cinder blocks remain level and plumb as I go?


I built a 14' chimney block pier (16"x16"x8" block) in my second floor garage observatory 11 years ago, to house my 12" SCT ... which is used exclusively for imaging. I only filled the first 4' of block with concrete and left the rest of the pier hollow. I've had absolutely no problems with vibrations when imaging. I've found this pier to be extremely stable even without filling it completely.

Keeping the pier plumb and level is very easy to do using a simple carpenter's level. The real problem is keeping it from developing a "twist" as the blocks are being laid. You need to be very vigilant to keep it straight ... however, for a 5' pier this shouldn't be much of a problem. Good Luck with your pier build.

#19 StarmanDan

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Posted 30 January 2013 - 10:07 PM

I only filled the first 4' of block with concrete and left the rest of the pier hollow. I've had absolutely no problems with vibrations when imaging. I've found this pier to be extremely stable even without filling it completely.


I have contemplated this too, but am stumped as to how I would interface the mount to the pier. How did you manage yours?

#20 roscoe

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Posted 31 January 2013 - 06:39 AM

You can keep twist under control by stretching a corner string or two from the base to some sort of temporary top support, and keeping the blocks near but not touching the string. masons use strings all the time to keep rows of blocks or bricks straight and even in height.

If you want to keep the blocks hollow most of the way up, you can stuff some newspaper plugs into the voids near the top, and just fill the last couple of courses with concrete, and set your j-bolts in that.

R

#21 *skyguy*

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Posted 31 January 2013 - 10:28 AM

I only filled the first 4' of block with concrete and left the rest of the pier hollow. I've had absolutely no problems with vibrations when imaging. I've found this pier to be extremely stable even without filling it completely.


I have contemplated this too, but am stumped as to how I would interface the mount to the pier. How did you manage yours?


I made a top-cap out of 3/4" plywood with a sheet of 1/4" hard rubber on the bottom (to absorb vibrations). It's bolted to the block at the corners using lead shields drilled into the block. Also, since the main attachment point for the wedge is at it's center, I embedded a length of 1/2" threaded rod into the concrete fill at the pier's base and ran it up and through the center of the block and through the top-cap ... to hold down the cap and to install the wedge. I also placed the threaded rod inside a 2" PVC pipe, filled with sand, to dampen any vibrations.

My 14' chimney block pier has far exceeded my performance expectations over the past 11 years. BTW, did I mention it cost me only $70 for materials and was built in only a few hours ... spread out over 2 days ... by myself and a friend with no block laying experience. :)

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#22 barbarosa

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Posted 31 January 2013 - 06:41 PM


I have to ask why any rebar is required.

Block/mortar or brick/mortar has worked for zillions of chimneys and walls. Most two-story brick/tile flue masonry chimneys here are still standing after the '06 and the '89 Loma Priata quakes. In fact, near the sections of freeway that collapsed in Oakland there are chimneys built before 1900 that neither cracked nor collapsed.

I am getting ready to do some sort of pier so these threads are educational.

#23 Gastrol

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Posted 31 January 2013 - 07:44 PM

I can see your point in not needing rebars, especially piers with a wide stance. But in my case without rebars, my 10" diameter concrete pier, about 6' tall including gear can develope a crack at the footing and possibly break.

#24 roscoe

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Posted 31 January 2013 - 11:52 PM

One of the most important reasons for putting rebar in a pier in colder climates is to prevent damage when the ground freezes. Frozen ground is larger than unfrozen (a volume of ice is 1/5 larger than the same volume of water) and when the ground freezes, the surface lifts, could be as much as 3-4 inches if the frost penetrates 3 or more feet, which it will in cold climates when under a structure which keeps an insulating blanket of snow away. When the soil freezes near the surface, it will adhere to the sides of the pier and attempt to lift it up. Rebar keeps the top part from being torn off the bottom part.
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#25 stmguy

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Posted 01 February 2013 - 06:11 AM

There also is a product that you can bind the blocks together on the outside of the blocks. I've used it and it works well.

There are different names but it usually has fiberglass fibers imbedded in it

http://www.quikrete....-Stack-Wall.asp
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