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  #1  
Old 02/17/12, 02:25 PM
 
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Cinderblock Root Cellar.(engineers help please)

Hey guys, I am considering making a root cellar/ underground storage building sometime in the near future. I was curious if there would be any issues with me digging a hole, pouring a cement flour 30x10x10 and then laying cinder block walls, placing rebar down the holes. Then I would go back and fill them with cement. After that I need to figure out how to put a solid roof on this thing. I would like for it to be 3 or 4 feet under ground. Does anyone have any ideas?

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Old 02/17/12, 08:14 PM
 
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they do that all the time. make sure you understand the forces at work. you need a grove in the cement where the center of the block will be to keep it from shearing and you need to install L shape bar into the floor that will go into every few cores or better yet every core. you will need to vibrerate the concrete as you fill the cores and make sure you have good laps on the rebar. you will also need to release the hydrolic pressures from behind the walls with some sort of drain tile. couple coats of thuro seal and a coat of black cat and its water resistant.

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Old 02/17/12, 08:17 PM
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Is this going to be literally a hole in the ground or will it be dug into the side of a hill.

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Old 02/18/12, 11:38 AM
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Tie the rebar in your walls into the floor slab - that's going to be you weakest spot. The best way is to pour your slab, lay the first course of block then use a hammer drill with a 1/2" bit in the cores you want to fill. The concrete will drill pretty easily especially if it is still green. Drive a peice of 1/2" rebar about 16" long into the hole with a hammer (drill your holes three or four inches deep) - you can get an epoxy filler to bond the bar in if you want but it is not required. The rebar will stick up a little above the first course but should be in the core of the second row. Lay up the rest of your courses (remembering where the cores are with the rebar then drop in a full length section from the top and slush full of concrete. As you are thinking of a solid top I would suggest that you run the rebar "wild" at the top (let it stick up above the wall a few inches) so you can then tie it into the concrete top when you pour it.

Typically when you pour a cap like this you build a temporary floor under it, pour with wire and rebar then remove the floor after it has cured. You can use plywood or OSB - often heavy corrigated metal is used and just left. You have to build it realy strong as it has to support all the weight of the concrete while it cures - do not skimp or you'll have a real mess. I would also consider pouring the cap with a slight slope to it so water runs off instead of pooling - not much but raise your form on one side 1/2" or so.

Be sure to do a good job of waterproofing both the wall and the top as it will wick moisture even if it is tight enough not to leak. Thoroseal is good but for where you are below grade I would go to a tar based product with a membrain and tile the permiter. I know - belt and suspenders - but it is much easier to do it when you build it than come back later if you have a problem.

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  #5  
Old 02/18/12, 05:23 PM
 
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Build the wall on footings and then pour the floor. That will keep the base course from kicking. Also you are going to use an enormous amount of crete filling all the cores. I stack the blocks on top of each other, not a running bond. Then I rod and fill the small cores where the blocks butt up. Surface bond inside and out and you will have no problem with leakage.

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Old 02/19/12, 10:12 AM
 
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Check this out
http://www.backwoodshome.com/forum/v...ad.php?t=19039

Or go down a few threads and read Coloneldad5's thread.

SPIKE

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  #7  
Old 02/19/12, 04:14 PM
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Quote:
Originally Posted by "SPIKE" View Post
Check this out
http://www.backwoodshome.com/forum/v...ad.php?t=19039

Or go down a few threads and read Coloneldad5's thread.

SPIKE

That is one sweet hideout!
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  #8  
Old 02/19/12, 05:01 PM
 
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Temporary wood to hold concrete on roof:









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Old 02/19/12, 05:07 PM
 
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Originally Posted by "SPIKE" View Post
Check this out
http://www.backwoodshome.com/forum/v...ad.php?t=19039

Or go down a few threads and read Coloneldad5's thread.

SPIKE
The bar joists ( metal truss things ) are way overkill in a span that size. You can go 12' or more easy with simply thick enough concrete and rebar.....all that is needed is some support underneath to hold it up while it's poured and cures. I've had a 10,000lb dozer parked on top mine while backfilling.
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Old 02/20/12, 09:56 AM
 
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That is one sweet hideout!
Thanks
SPIKE
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  #11  
Old 02/20/12, 10:03 AM
 
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Originally Posted by TnAndy View Post
The bar joists ( metal truss things ) are way overkill in a span that size. You can go 12' or more easy with simply thick enough concrete and rebar.....all that is needed is some support underneath to hold it up while it's poured and cures. I've had a 10,000lb dozer parked on top mine while backfilling.
Hey TnAndy, Looks like you do good work!

I had the bar joist and marine grade vinyl on hand. It made for a nice clean finished ceiling. I did not have to remove any forms or supports after pouring. And they work well for supporting shelves or hanging bags of vegies from.
As far as strength goes, you are right it was overkill.

SPIKE
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  #12  
Old 02/20/12, 03:24 PM
 
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All of this is excellent information. Thanks so much guys. Dirtman, are you saying that I should lay the slab with rebar coming out and then dry stack the bock and then fill it?
Also Dirtman... is filling just the small gaps enough to hold the pressure of the dirt pushing on it?


T-bone can i just lay 16' rebar into the slab when its poured so i can skip the drilling and hammering it in? I will be following your advice of making the roof sloped.

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Old 02/20/12, 05:27 PM
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Your concrete supplier should have Q deck in stock to use as the ceiling/form for the roof slab. That eliminates the need for supporting the roof slab from below when you place the concrete.

The key to preventing the walls from cracking or allowing water to leak through in the future is to not back fill with clay. Eventually, whether it is ten years or fifty years from now, the clay will destroy the integrity of the walls by cracking or collapsing them. I had a friend set in his basement family room and watch one of the block walls collapse. Ive seen tract houses built that always had wet basements during heavy rains.

Use geotextile and drain tile around the perimeter (holes down) and back fill with clean granular material (sand or pea gravel). Back fill within a few inches of the final ground surface before overlapping and sealing with the geotextile.

If you build the french drain around the perimeter correctly you won't need the rebar in the block if you lay them up with mortar. If you do use the rebar in the block and it's tied into the base and roof, use grout in the cells or at the largest concrete made from pea gravel. When you use a vibrator on the concrete, do not allow it to touch the rebar.

If the root cellar is dug into the ground on all four sides, you still have to daylight the french drain. A GF bought a town house where the basement got wet because the contractor never daylighted the perimeter drain. She finally sold the place when she got transferred rather than keeping it to move back into after she was transferred back.

Installing the french drain correctly is the simplest way to protect the walls from the earth pressure and prevent water intrusion.

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  #14  
Old 02/20/12, 05:57 PM
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When you back fill do it with Stone and Sand. dirt and clay put pressure on the walls. Sand and stone forces go down not into the wall. What generally happens when you backfill with dirt is the wall is forced in a t frost line. You can see it in old block home foundation and basements all the time. The stone and sand eliminate that. you can put a few inches of dirt on top for grass

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  #15  
Old 02/20/12, 06:12 PM
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Quote:
Originally Posted by Wigglesdabum View Post
T-bone can i just lay 16' rebar into the slab when its poured so i can skip the drilling and hammering it in? I will be following your advice of making the roof sloped.
Sure but be aware that if you do that you have to measure carefully so that the bar stick up into the core of the block or you'll have problems.
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Old 02/20/12, 06:18 PM
 
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OK so I have never worked with concrete in my life or moving soil , except digging fighting positions in the Marine Corps hah. Im going to give you a run down of what I understand so far.

1: excavate area
2: lay french drain, line with geotextile, and a drainage pipe, holes down
3: insure its daylighted.(if its not possible to get it daylighted can I run it to a drywell?)
4: fill with pea gravel
5: lay the slab with rebar and mesh
6: insert 16' rebar vertically around the perimeter , while the slab is still wet.
7: lay the walls conventionally.
8: insert rebar vertically (every gap for me) leave extra extended
9: fill with cement, (3000 psi) using vibrator
10: build reinforced ceiling form, bend rebar over into ceiling form
11: lay mesh , and pour cement. with 1 side elevated slightly.
12: refill thehole with pea gravel all around the structure then cover top with dirt.


(deep breath) did I get it all hahah

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Old 02/20/12, 07:06 PM
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1: excavate area
2: lay french drain, line with geotextile, and a drainage pipe, holes down
2: line what will be the french drain with enough geotextile to extend above the depth of excavation and over lap, install the drainage pipe, holes down
3: insure its daylighted.(if its not possible to get it daylighted can I run it to a drywell?) Yes, just make sure that it is not subject to ground water intrusion.
4: fill with pea gravel
5: lay the slab with rebar and mesh I'd do the slab before doing anything related to the french drain other than excavation.
6: insert 16' rebar vertically around the perimeter , while the slab is still wet.
7: lay the walls conventionally.
8: insert rebar vertically (every gap for me) don't need rebar in every cell and probably not at all if the french drain is done correctly. leave extra extended
9: fill with cement, (3000 psi) use grout or concrete made with pea gravel.using vibrator You won't need to use a vibrator in the cells.
10: build reinforced ceiling form, (use Q deck to save money and time) bend rebar over into ceiling form
11: lay mesh , and pour cement. with 1 side elevated slightly.
12: refill the hole with pea gravel all around the structure then, fold geotextile over and overlap cover top with dirt.
13. For slabs run a stiff mix for strength. Slump around 4". In other words, you don't want a soupy mix. Soupy equals weak.
14. If you're working short handed ask your concrete supplier about adding Delvo to slow setup..
15. Spray the concrete slabs with a curing compound after you're done finishing especially on a hot day. Keep the concrete wet for about a week to properly cure if you can't spray it with curing compound. That will help keep the floor from dusting if you don't over work the concrete. Wet burlap works fine or plastic with a garden hose underneath to occasionally add water if you don't want to use curing compound.

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Old 02/20/12, 08:34 PM
 
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You have been so amazingly helpful man. I now feel like I could actually complete this job on my own. I have just a few more questions.

-What is a slump of 4"? Do you mean make sure its at least 4 inches thick?
-Are you sure that just using pea gravel concrete is strong enough to withstand that amount of dirt?
- With the geotextile, will I have 2 layers of geotextile with the gravel inbetween or will it go like : The concrete wall, then gravel, then one layer of geotextile? I hope you can understand my question.
- How do you make the layer of gravel be uniform all the way up to the top? Do you pour a little then fill in some dirt around the geotextile then pour more gravel and repeat?
- last question, should I run geotextile under the bottom slab before I pour or just under and up the sides and over the top?

I cant explain how much information I have gained from you. Thank you so much.

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Old 02/20/12, 10:20 PM
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The slump is a measure of how much water has been added to the concrete mix. Ask the concrete dispatcher to send you a driver that's been there for a bunch of years. Tell the driver you want a slump of around 4". He'll get it close enough.

Unless you pour reinforced concrete walls, the wrong backfill will eventually cause them to fail. The cement grout or the small aggregate (pea gravel) concrete mix you use to fill the cells can be soupy. Grout is not the same as mortar.

When you're done the geotextile will be the closest thing to the outside of the hole you dug. It will be below the drain tile and be the closest thing to the block walls. All of the granular material you use as backfill goes inside the geotextile. You should have geotextile up above the ground on the edge of the hole and coming almost as far up alongside the block wall. when you get the back fill a few inches, maybe six inches, below the surface of the ground fold and overlap the geotextile over the top of the backfill so it surrounded by the geotextile. The geotextle will surround the backfill on the bottom, the tops and all sides. that will keep soil from infiltrating and blocking the french drain long after you're gone.

Don't worry about the french drain until the cellar is finished. At that point lay the geotextile out, put the pipe in and start putting the backfill in.

It wouldn't hurt to put a small ditch around the bottom side of the hole away from the slab draining to a sump you can use to set a sump pump to keep the hole dewatered.

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Old 02/21/12, 09:54 AM
 
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Originally Posted by Wigglesdabum View Post
All of this is excellent information. Thanks so much guys. Dirtman, are you saying that I should lay the slab with rebar coming out and then dry stack the bock and then fill it?
Also Dirtman... is filling just the small gaps enough to hold the pressure of the dirt pushing on it?


T-bone can i just lay 16' rebar into the slab when its poured so i can skip the drilling and hammering it in? I will be following your advice of making the roof sloped.
The surface bonding alone will keep the walls stable. I mostly fill the small voids for added stability as I'm building up the wall. I guess I'm old school, but I always build on a reinforced footing, at least 16 inches wide and 8 inches thick with two 1/2 rerods spaced four inches in from the edge of the footing. After the wall are up then I pour the 4 inch slab When that sets up the bottom of the walls can no longer be pushed in by the backfill. If you try to build your wall on top of the slab then you will have to anchor at least stub rods into it to keep the walls from thrusting in when you back fill.
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