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Opinion: native soil or liner in pier base

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13 replies to this topic

#1 Alex McConahay

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Posted 11 December 2018 - 10:16 AM

I am of the opinion that the concrete poured into a hole that will be a pier base should be poured directly into well compacted soil.

 

A colleague of mine says line it with a plastic liner, and then pour the concrete.

 

What says the collective wisdom of Cloudy Nights?

 

Alex

 



#2 Real14

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Posted 11 December 2018 - 10:21 AM

Hi Alex,

 

Neither of both. I am not a civil engineer but my guts say that one should pour the concrete into a hole which was cleaned well from all debris which happens when one digs a hole.

 

With the plastic liner I see one problem and that is that hunidity will be always trapped inside the concrete ... ¿ is it good, is it bad ? I do not know but I do not like the idea of having always humidity in my concrete base ...

 

IMHO but I can be wrong ...


Edited by Real14, 11 December 2018 - 11:20 AM.


#3 CharlesW

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Posted 11 December 2018 - 10:32 AM

That seems like a completely unnecessary waste of time and effort. Even my pier at GMARS hasn’t shown any signs of cracking despite being poured in that talcum powder that purports to be sand. I’m sure the water got sucked out of that mix about 10 seconds after it touched the ground. 


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#4 gardenfish

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Posted 11 December 2018 - 10:46 AM

I would not use plastic in the hole. I did not for my pier. I watered mine 2-3 times a day for a couple days after pouring to help with curing and around here they put plastic on top after pouring slabs to retain moisture for curing.

 

 

Rick



#5 tolgagumus

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Posted 11 December 2018 - 12:13 PM

What would be the advantage for using the plastic. I have worked as an electrician for 25 years and I have never seen plastic under a footing. 

 

I will say something about compacting. The bottom of the hole should be undisturbed soil. Don't dig 2 feet deeper, fill it back up with soil and compact it. It will settle. If you need to come up, use crushed stone. 


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#6 Alex McConahay

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Posted 11 December 2018 - 01:30 PM

Tolga--When I say "Compacted" I mean to make sure there is no loose soil down there, not that we dug deeper, and then backfilled. In our case we are talking loose sand in general. Whenever one digs, sand can slide into the hole a bit. Not much at that depth, but a bit. So, we always made it a point to clean out the hole of anything loose, and then stomp the bottom of the hole with a compacter (basically a the end of a 4x4 that we pounded into the ground). 

 

Alex



#7 DeanS

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Posted 11 December 2018 - 01:44 PM

Building footers are normally poured without a plastic barrier.  Floors typically are so they have a mositure barrier.  Seems like if you lined it with plastic it would slow down the curing, which is not a bad thing.



#8 sink45ny

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Posted 11 December 2018 - 01:46 PM

I poured both of my piers into native soil. 



#9 choward94002

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Posted 11 December 2018 - 02:26 PM

Pouring with plastic is done to keep the curing rate constant; concrete needs to remain relatively damp for several days to properly cure.  If you're pouring into soil that's too wet or too dry then plastic is used to retard the moisture transfer while the concrete cures.  It won't make a bit of difference in terms of the hole stability (and of course as others have mentioned always pour onto undisturbed soil and have as little disturbed on the sides to backfill with a gravel/ sand mixture) ...

 

If you're unsure then it's safer to use plastic, just be sure to allow for an extra few days to let the concrete cure ...



#10 roscoe

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Posted 12 December 2018 - 07:52 AM

In really sandy crumbly soil, a plastic bag might be a good option, to prevent clumps of sand from falling into the concrete as you fill the hole...or if your subsoil is really dry and would want to suck the moisture out of the concrete.  Cure time win't be affected much either way, concrete cures by chemical reaction, not water evaporating.  You just want enough water in there so it is present for the chemistry to work, so sucking the water out of the edges could leave the edges soft and crumbly, which in real life won't matter much with a foundation, but would make your pier shed sand forever....

 

I'm a carpenter, I've filled a hundred holes with concrete, and never lined one.....



#11 tolgagumus

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Posted 13 December 2018 - 06:47 PM

Tolga--When I say "Compacted" I mean to make sure there is no loose soil down there, not that we dug deeper, and then backfilled. In our case we are talking loose sand in general. Whenever one digs, sand can slide into the hole a bit. Not much at that depth, but a bit. So, we always made it a point to clean out the hole of anything loose, and then stomp the bottom of the hole with a compacter (basically a the end of a 4x4 that we pounded into the ground). 

 

Alex

Alex, my comment was more for people who might read this in the future. 

 

I can think of one reason why one want to use a liner. Sometimes we can prepare the hole, set the sonotube in the ground, back fill around it but may not be able to pour the same day. The tube may soak the ground water and collapse. In this case we can put it inside plastic. 


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#12 Alex McConahay

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Posted 13 December 2018 - 09:26 PM

More details. Colleague is suggesting using plastic food storage containers.

Alex

#13 choward94002

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Posted 18 December 2018 - 12:39 AM

More details. Colleague is suggesting using plastic food storage containers.

Alex

I assume he's wanting to replicate a BigFoot footing [https://www.lowes.co...g-Form/50213065], which is a bit overkill for a telescope pier but sure, OK ...

 

Otherwise, unless you can ensure good compaction of the backfill around the plastic food container I wouldn't suggest this ...



#14 roscoe

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Posted 18 December 2018 - 07:48 AM

Proper compaction of any backfill is the key to stability for any pier.  That mostly means putting a couple inches of dirt in, ramming it down well (the end of a 2x4 works good), and repeating that, in 2" lifts,until the hole is full.  That is mostly not possible with a sonotube-type form, it'll crush the tube....so wait at least a couple of days for the crete to harden before backfilling. A large hole dug by a backhoe can be quite a chore to backfill, I always try to dig any pier holes with a post-hole digger and/or small shovel, (or power auger) to minimize the disturbed soil I must put back.

 

You're doing the best possible by making sure all below the pier is well-compacted.

 

There are available at most real lumberyards one-piece tapered plastic forms that are stiff enough that they can be backfilled before pouring the crete, that is a nice option, because you are not working over an open hole.

 

Here's one I've used:

https://foottube.com/


Edited by roscoe, 18 December 2018 - 07:52 AM.



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