Stumps under new slab?

[swharris]

Is there any acceptable amount of old ground down stump that can safely be left in ground and poured over? My contractor is saying yes, but I can't think a rotting trunk soon to be a void could be anything but bad.

On a second tangent, we have mostly clay here where I'm at (N. Orange County in Southern CA), but the area I'm building had many trees and lots of drop. What is the SOP for prepping the site? The site is flat with 0 slope.

WWGJ do?

A rare soggy afternoon here last week. This type of rain is historically very rare and usually short lived. Building will front ally in background. First pic is South(L) and second is North(R) sections of lot. It's mostly clear now. Anyone need some older Anderson vinyl windows or tires? FREE!;-

You can see how much organic material was there before.

 

[firworks]

Depending on the tree I don't know if I would trust that... I have an underground Rhizome in my front yard from a neighbor's tree 30 years ago that causes tiny trees to sprout up EVERYWHERE on the whole south side of my property. If I don't keep up on them they get to be a couple feet tall in short order. I'd be worried about leaving a tree underground under a new slab. I don't have exerience with it in your specific setup but I just know that leaving behind the roots of a tree can be a big pain in the ***.

 

[Bob275]

I'd say none, dig them out, backfill and compact in lifts. I have two in my yard and am constantly dealing with sink holes because of them. Wouldn't want that under a concrete floor.

 

[machsnell]

Absolutely not. Good subgrade should have no organics (roots stumps for you) and topsoil as well as soft subgrade should be removed.

If you leave a stump in a yard you will see the depression in the yard as soon as it decays. Same thing would happen under your slab. You are correct and don't want voids under you slab.

I dont understand your question on lot. You said had lots of drop (?slope) and then said it had 0 slope.

If it has no slope raise your slab and building and create some.

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[swharris]

I dont understand your question on lot. You said had lots of drop (?slope) and then said it had 0 slope.

If it has no slope raise your slab and building and create some.

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So sorry. Lots of tree leaf drop and organic debris. By drop I was referring to tree "droppings".

 

[swharris]

Depending on the tree I don't know if I would trust that... I have an underground Rhizome in my front yard from a neighbor's tree 30 years ago that causes tiny trees to sprout up EVERYWHERE on the whole south side of my property. If I don't keep up on them they get to be a couple feet tall in short order. I'd be worried about leaving a tree underground under a new slab. I don't have exerience with it in your specific setup but I just know that leaving behind the roots of a tree can be a big pain in the ***.

The tree in question is a Carob. Very hard wood apparently.

Like this, but about 10 times as big.

 

[paranoid56]

here is a kinda interesting thing on that subject. but if it was me, i would tell him to dig it out, hes being lazy.
http://www.smithsonianmag.com/scien...-dangerous-sand-dune-swallowed-boy-180953404/

 

[mkbug]

When building a home in SoCal (Oxnard) we excavated 5 feet down and brought back in clean fill in lifts that were compacted. Then a soils inspector had to check the work before signing off. Not sure if this is something that should be considered in your build.

 

[Dr Stan]

Absolutely not. Good subgrade should have no organics (roots stumps for you) and topsoil as well as soft subgrade should be removed.

If you leave a stump in a yard you will see the depression in the yard as soon as it decays. Same thing would happen under your slab. You are correct and don't want voids under you slab.

Had a colleague in MS who's house slab had been built on top soil the contractor removed from another portion of the lot. MS has a law requiring a 10 year warranty on foundations due to a lot of various strange soils across the state and contractors trying to take the easy way out. Yazzo county clay is one of the most notorious. He was within the 10 yr time frame, but still had to sue the contractor as his attached garage was breaking off the main portion of the house.

So, do not let the contractor build on top of organics. My concrete contractor made it quite clear a couple of trees had to go to pour the slab for the shop. One was dug out and hauled off. The other one was a magnolia we moved and managed to save even though it died back and had no live branches for close to a year.

Three dump truck loads of dense grade were unloaded on the building site and packed long before a single drop of concrete was poured.

 

[LXCam]

You need to watch the myth busters episode where they were checking the myth about bambo growing thru someone used by the Japanese during WWII. Heck if you're lucky you could be the first guy ever with a treehouse shop.


But on a more serious note dig it out, period. The chances it'll die are very high but it will also rot in time. Not knowing how big it is or if it's surface rooted could potentially cause you some grief in the long run. If it's small you could use a high dosage of killer as well as driving a cooper stake down into the stump.

Edit, just got a chance to get on a puter and saw the example you showed where you stated it was 10X that size. No if's, and's or but's it needs to come out. How does your contractotr plan on digging his footings, I'd imagine a back hoe right?. Tell him to remove it and backfill with a suitable material. He could use the natural he removed for the footers but that'll take some effort getting compaction. Personally I'd have either 3/4 rock or just sand brought in just to make compaction easy.

 

[machsnell]

When building a home in SoCal (Oxnard) we excavated 5 feet down and brought back in clean fill in lifts that were compacted. Then a soils inspector had to check the work before signing off. Not sure if this is something that should be considered in your build.

It is important to get rid of stumps and extensive root systems.

As for the bad soil you might need to go a couple of feet down but you would never need to go deeper than a few feet for a slab, footings yes.

A slab floats and you can bridge with surge stone and regular mixed stone (named differently everywhere) like you would use for a driveway. Add some fabric or grid and you can usually build up a solid pad in a few feet if you are being smart about it. Roads have been built through the swamps of Louisiana and Florida.

Good luck.

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[swharris]

You need to watch the myth busters episode where they were checking the myth about bambo growing thru someone used by the Japanese during WWII. Heck if you're lucky you could be the first guy ever with a treehouse shop.


But on a more serious note dig it out, period. The chances it'll die are very high but it will also rot in time. Not knowing how big it is or if it's surface rooted could potentially cause you some grief in the long run. If it's small you could use a high dosage of killer as well as driving a cooper stake down into the stump.

Edit, just got a chance to get on a puter and saw the example you showed where you stated it was 10X that size. No if's, and's or but's it needs to come out. How does your contractotr plan on digging his footings, I'd imagine a back hoe right?. Tell him to remove it and backfill with a suitable material. He could use the natural he removed for the footers but that'll take some effort getting compaction. Personally I'd have either 3/4 rock or just sand brought in just to make compaction easy.

The main stump is about 2' in diameter and has significant surface roots. He says he has tried to pull one out like it before and his back hoe would not budge it. Now, with that said, I can't see how a good sized BH would not be able to dig around it and yank it out. We'll see I guess. I'll try and take a picture and post it later on. It's dark now, but I'll give it a try.

 

[James-W]

I am in agreement with getting rid of the stumps as well as the roots. To leave the stumps and roots there is sort of like an accident waiting to happen. The whole issue here is, the stumps and roots won't rot right away, it will take a few years for that to happen. So you won't have any problems initially. By the time you start to have issues the concrete guy will be long gone and you will be stuck dealing with the problem. You really need to be proactive and deal with it now before it becomes a problem.

 

[Dr Stan]

One more thing, have the excavation treated for termites before the concrete is poured. It should not cost much and will give you lifetime insurance against termite infestation.

 

[machsnell]

^+1

This is excellent advice. I wish I had know to do that when i was building.

A backhoe can pull any stump. It's just a matter if time and a decent operator. Don t believe that ****. You are correct dig around it and you have to cut under it as well. Sometimes a stump will look like there is nothing holding it to the ground but the stubborn tap root will hold it there. You want to remove the roots as well.

It sounds like more work than it is. For aa small garage and a decent operator a backhoe can grub out the roots in no time.

Remember when the stump is removed and roots are grubbed out the hole created via excavation needs to be compacted back well with a jumping Jack or decent sized (48" min) roller. Lots of concrete guys I see use a plate tamper for their dirt and their stone compaction which isn't enough.

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[73RR]

NO organics!
NO plate compactor.
If you have any concerns about the size of the hole or the quality of the proposed fill material then use crusher reject or ¾-0 for fill and compact in lifts.
You will not be happy later on when the cracks start.

 

[77thor]

... if it was me, i would tell him to dig it out, he's being lazy...

This ^^^

 

[swharris]

UPDATE: New stump grinder came with the proper tracked machine and made short work of all the remaining stumps. Looked something like this.

Grading and compacting to start this week if the rain stops on Wed. Good suggestion on the termites as they are definitely around here.