Subbase type for slab - why shell shouldn't be used

[Ryan29]

Can anyone find documents that show shell shouldn't be used as a base for garage slab? I couldn't find anything other than one thing referring to the Galveston area that used shell up until the 1960s and that shell base slab is much more difficult to fix/level than gravel base type. But I want more ammo when I talk to the concrete guy.

Wish I knew more about this subject

It's gonna be a 4-5" slab with 4" base compacted for a detached garage.

Pros and cons of using shell as subbase for slab

 

[pamike]

I think you mean shale? As in a soil that is made up primarily of small flat rocks?
If thats what u mean I wouldnt hesitate to use it as long as its very rocky and has very little dirt in it. We built a 50 x160 building in 1984 using packed shale for the base. It's our best floor in the entire building.

 

[larry_g]

I do believe he is referring to sea shells.

lg
no neat sig line

 

[Lucky Llama]

Shell makes fantastic base. When it was available it was by far the best base.

 

[like2wheel]

Unrelated, but the base under the slab of my attached garage consists of thousands of broken pieces of china.

 

[lakeroadster]

Wish I knew more about this subject

The key is to use fill materials that have known Proctor density data and to be up front with the excavator and site prep sub-contractors.

More here: https://www.garagejournal.com/forum/showthread.php?t=346747&highlight=Proctor

 

[WNYflyer]

Well in the construction industry the term "shell" is simply too generic in nature. What are the specifications for the "shell" base/fill? Is it a local DOT approved base/fill?

It looks like the Florida DOT (FDOT) has approved shell type bases/fill that might help your search. Pretty technical in nature but it is what it is.

https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/programmanagement/implemented/specbooks/january2019/files/911-119.pdf?sfvrsn=c6951124_2

 

[ConCretin]

I'm not familiar with using 'shell' under a slab but I'm curious. Is there some concern about the existing sub base or do you need to bring up the grade? Is shell less expensive? I wouldn't take a chance unless you are sure.

My other question is how tightly shell can be compacted. If the material moves around under foot traffic, you could end up with an uneven surface and thin spots in your slab.

 

[Falcon67]

>I think you mean shale? As in a soil that is made up primarily of small flat rocks?

Shells as in sea shells. Used to lay the off payment roads with it down there. From going to the coast regularly with the family as a kid, that's all I remember of the roads after you left the regular pavement. Have no idea how they got it in large quantities. It's tough stuff, should be just as good for base material as our "bin 10", crusher run, etc.

 

[SGKent]

the only thing that comes to my mind is that any acidity in the water or soil adjacent to the shell, even minor acidity, will dissolve it. Over time most soils become acidic so shell eventually breaks down. That said, if the soil is alkaline then the shells last forever. Oyster Shell lime for example is ground up shells. You use it to neutralize acidic soils. Shells also have to be crushed and compacted well I would think because of the curves and hollows. I do remember driving on shell paved roads in FL once in a lite rain and it was almost like being on frost on a road.

 

[Kaizen]

Driving in shell base is a lot different then putting under concrete. Doubt any concrete guy will guarantee a job if not done in normal base. When I can’t find documentation I follow local builders practices.


Sent from my iPhone using The Garage Journal mobile app

 

[bigdav160]

Galveston? At one time Galveston wasn't considered a good port because of the huge oyster reef that extended 20 miles all the way across the bay with only a small opening that a flat bottom skif could get through.

In the 19th and 20th century that reef was mined out and used for road base. It seemed every road and driveway base was oyster shell.

Oysters seed and grow on top of older reefs. Removal of the large reef had a serious detrimental effect on the water quality in the bay.

Today, the oyster shell is recycled back into the bay to help reestablish the oyster population.

I have no idea how it will work as a base for a slab although I am sure many many miles of roads are paved over old oyster shell.

 

[pcmeiners]

Agree with SG.....

"the only thing that comes to my mind is that any acidity in the water or soil adjacent to the shell, even minor acidity, will dissolve it"