Concrete Base Layer Question

[Wolfeman78]

Hello all I am just starting my 30x40 garage project. My contractor decided to build up my foundation with a med sized rock along with some crushed rock. It all looked good but it is about 3ft thick on the backside and he did not compact the layers. When I asked him he said this mix did not need to be compacted. Does this sound right?

 

[kd3pc]

If it is freshly built up, it will likely need compaction, especially if the 3' was done all at once.

What did the contract say?

What is the underlying soil like?

3' is still a lot.

 

[brownbagg]

its kinda a myth when talking about compaction of rock, yes its need compacted but it can't be tested due to voids, that why most contractor feel compacitng of rock is not needed. but as it, it like building on top of marbles, the rocks going roll around till they settle down and lock together

 

[ConCretin]

Washed and/or crushed stone doesn't require mechanical compaction. Just be aware that fines from adjacent materials can wash into the stone fill if water is present It obviously won't hurt the stone fill but it creates the potential for settlement around it. Otherwise, stone is a great fill material because it gets you as close to 100% as possible.

 

[Wolfeman78]

If it is freshly built up, it will likely need compaction, especially if the 3' was done all at once.

What did the contract say?

What is the underlying soil like?

3' is still a lot.

He said that the fine mix with the medium rocks will be fine. The guy grading the foundation and finishing up form boards said it prolly should have been compacted by layer. I may amend final contract to guarantee no cracking of crumbling. I may just be to paranoid..

Soil underneath is solid..

 

[Wolfeman78]

Washed and/or crushed stone doesn't require mechanical compaction. Just be aware that fines from adjacent materials can wash into the stone fill if water is present It obviously won't hurt the stone fill but it creates the potential for settlement around it. Otherwise, stone is a great fill material because it gets you as close to 100% as possible.

Great! I don't know much about any of this .

 

[radrush]

its kinda a myth when talking about compaction of rock, yes its need compacted but it can't be tested due to voids, that why most contractor feel compacitng of rock is not needed. but as it, it like building on top of marbles, the rocks going roll around till they settle down and lock together

When dealing with rock we don't call it compaction; we call it consolidation. Open graded aggregate, rock, when used for foundations must be well consolidated: a jumping jack compactor or a plate tamp should be employed to consolidate the material.

I prefer the use of the jumping jack for this type of work because if the side walls of the earth excavation are soft, the jumping jack will pound the open graded aggregate into it.

 

[radrush]

its kinda a myth when talking about compaction of rock, yes its need compacted but it can't be tested due to voids, that why most contractor feel compacitng of rock is not needed. but as it, it like building on top of marbles, the rocks going roll around till they settle down and lock together

^^^^This...the above brief statement contains much wisdom...allow me to elaborate.

What's NOT a myth is that contractors will do ANYTHING to get out of doing a little bit of work. The only thing this contractor knows is that compacting/consolidating the stone will cost him the rental fee on the equipment and the labor to do it. So voilà, "What you got there (you dumb unsuspecting homeowner) is (magic) self-consolidating stone."

The consolidation of the stone can not be tested for density (degree of compaction) directly but it can in fact be tested. There is no ASTM standard test method for either one of these but both your ears and your vision can be used for this testing. For instance if your contractor says something as dumb as "stone is self-consolidating" or if you don't see the contractor running a jumping jack or a plate tamp, well, there you go, it isn't consolidated.

Depending on the thickness of the layer, crushed stone that has not been properly consolidated runs the risk of creating long-term settlement problems. Not problems for the contractor you understand, because he'll be loooooooooong gone.

By the way, not "worthless", but we need some pics...

 

[Wolfeman78]

by the way...

Let me see if I can post some up.

 

[Wolfeman78]

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Pics up

 

[Wolfeman78]

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[Wolfeman78]

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[BillK]

I am certainly not a foundation guy, but that just does not look right to me. Are the foundation walls going to be part of the entire pour ? If so I would hope that the stone was compacted. Looks like a formula for future cracks.

I think I would call a halt until you can get someone else to look at it. It would be well worth paying a few bucks to have an engineer come out and take a look in my opinion. Or at least call the building inspector and see what he thinks ? He has to sign off on it anyway.

 

[Wolfeman78]

Yeah he plans to pour solid concrete walls.

 

[Zeke]

Lotta material is going to be wasted there. I certainly would not build that way. For that kind of fill I would likely accept a tractor with a grade bucket having run all over that as it was being placed. NO reason to not have a jumping jack on site for the areas the tractor can't get to. But not having at least part of a stem wall and some rebar just won't work for me.

But I don't build pole barns in the woods.

And when you guys say the contractor will be long gone is that assuming all contractors don't live in the area and own homes. I mean if you deal with a Gypsy from nowhere, I can agree. Most people with any equipment are going to work in a 100 mile radius, give or take. Beware of the contractor with a motorhome and a POB.

I am certainly not a foundation guy, but that just does not look right to me. Are the foundation walls going to be part of the entire pour ? If so I would hope that the stone was compacted. Looks like a formula for future cracks.

I think I would call a halt until you can get someone else to look at it. It would be well worth paying a few bucks to have an engineer come out and take a look in my opinion. Or at least call the building inspector and see what he thinks ? He has to sign off on it anyway.

Not all areas require inspections.

 

[Chaznsc]

Too many fines in that material not to be compacting in 6 to 12 inch lifts.

 

[Wolfeman78]

He lives close to me and built my neighbors barn. His subs did awesome work on my neighbors, mine hmmm... I do not have to have an inspection so I might have to get a third party to look at this for me. I asked him to pour walls or block it but he told me this would be just as good.

 

[flat350]

I don't do concrete,I'm a plumber.In the work we do CA-6 (3/4 and fines) stone is required to be compacted in 6" lifts yet if I use CA-7 (3/4 no fines)stone no compaction is required and many of the GC's do have a man on site daily to test the compaction of all of our fill and he signs off on it in writing.They use a nuclear gauge not the proctor test.

 

[radrush]

I don't do concrete,I'm a plumber.In the work we do CA-6 (3/4 and fines) stone is required to be compacted in 6" lifts yet if I use CA-7 (3/4 no fines)stone no compaction is required and many of the GC's do have a man on site daily to test the compaction of all of our fill and he signs off on it in writing.They use a nuclear gauge not the proctor test.

They use the nuke gage to test the density of the in-place compacted material. The gage readings are compared to the results a proctor test, a test that was performed on the material either in the field or back in the lab.

Here's a pic of a guy (not me) running a nuke test with a Troxler.

Yeah he plans to pour solid concrete walls.

So basically this is a turn-down slab with really deep turn-downs.

In those pics, that stone does appear to have a lot of fines, sand and smaller stones, that fill up the voids between the larger stones. A qualified engineering technician with the right equipment could get a density/compaction test on that material.

How thick is the stone layer on that upper flat area?

Easy test, put your work boots on, go out there (on the upper flat area) and stomp the stone with your heel. If you can indent the surface more than 1/2", it isn't consolidated. Take pictures of both and post.

Can you take and post more pics of the other side of the building pad, like where the main entrance will be.

 

[Wolfeman78]

[URL=http://s1202.photobucket.com/user/Wolfman781/media/Mobile%20Uploads/90265A08-7941-477C-8AB7-05D3FD273D0A.jpg.html] [/URL]I can post more pics in a little bit.[URL=http://s1202.photobucket.com/user/Wolfman781/media/Mobile%20Uploads/5C57A9E1-7170-4441-BCAE-16C9B48C7854.jpg.html] [/URL]

Upper flat area is only 6-8 inches thick. The material is a mix of med stone, small chips, and powder.

 

[Zeke]

How is that water bottle going to compact?

I think the thing here is experience. If the contractor built the neighbor's project and there's no complaints or defects, that's good. But of the projects completed how many are filled 3 feet with your soil condition? If he has a good answer to that I'd have a better chance of trusting his judgement over ours. Well, mine anyway.

I just couldn't waste (pay) for that much concrete for a 'turn down' slab. Where's the savings? Why not just fill the whole damn thing 8 inches thick?

 

[radrush]

There a couple of things to consider.
Prior to the placement of the stone:
1. the top soil and all traces of organic material should have been removed
2. the slope should have been "benched" back so that the rock wasn't placed directly on a slope...like this...

...................._____
..............___/
.......___/
___/

This stone thing is easy enough to fix. Get a backhoe in there and dig the rock out. Place the rock in a pile outside of the entrance of the garage. Replace the stone in 6" - 8" lifts with a rented one of these...

 

[spike99250]

The transition area from the front area(which will be a slab)to the area that haunches off into wall portion is going to be a problem. I would worry about cracking and possible curling in that area.

 

[Wolfeman78]

I am going to talk to contractor again tomorrow. Thanks for all the info

 

[pstnbly]

As an excavating and concrete contractor it never ceases to amaze me some of the jobs that are posted here and what some contractors will try to pass off as acceptable. Not only has the aggregate not been properly placed nor compacted in lifts appropriate to the granularity of the material (see radrus post), but there is an insufficient bench created for footing placement around the perimeter of the floating slab to prevent slippage. A very problematic situation all around IMHO.

 

[Caterpillar Cowboy]

+1 more vote on having too many fines not to be compacted. I've seen the bases for slabs done with both crushed road base, and washed rock and chips, but whichever method is chosen it had ought to be done right!

 

[C96]

This looks like trouble waiting to happen. I think steel reinforced stem walls, or cinderblock fully grouted with proper foundation, then backfilled and compacted as needed for the slab. It seems corners have been cut here and a recipe for future problems, settlement, cracking, shifting, sliding, etc.

The gravel looks to have been just dumped and raked out over the ground without any prep work directly on existing grass, weeds, or whatever foliage that happened to be there as shown in the picture below.

I wouldn’t be happy with this.

 

[Slednut]

My excavator spent a lot of time compacting, when he was done it looked and felt like concrete. The red circle shows what it looked like..

 

[Wolfeman78]

I guess I am going to gear up to argue with my contractor tomorrow. He told me that if I had any problems with slab he would break it up personally. Yeah right..

 

[cderalow]

If he's placing on the side of a slope, there should be some sort of engineered foundation plan.

If not, man I need to move to a rural area... it'd save me a ton in consultants costs.

 

[SwampCat]

As a soon to be retired excavator, after 32 years of this stuff. There is NO WAY IN HELL that would PASS any of the jobs I work. That deep fill on the back end is TROUBLE. Like has been said , not stepped so the fill can LOCK in. TOO much fill at once. And I dont care WHAT kind of stone you are using, you compact EVERYTHING. Its not uncommon to OVERfill the pad by 4 to 6 feet, usually as a kindness to the other trades to have a SAFE place to set scaffolding ie. brickies, siders, roofers, ect.

 

[JimR1998]

Not apples to apples, but for a concrete pad I recently had done the contractor rolled over it with a track digger and it did not leave any indentation. It displaced stone dust on the surface and that's about it. He used a plate compactor every few inches to get it tight.

Question: On a job like this where a lot of fill is required, can compacted dirt be used for the bottom layer and then use stone only on the top 8"-12"? Just wondering.