crushed stone help

[Kapt]

I'm getting all kinds of advice from the "professional" concrete contractors about what kind of crushed stone to put under my slab. One guy said do not use CR6 under any circumstances because of some settling issue while another guy says to use CR6. Another guy said to use #57 stone without compacting because he says it's a non-compacting stone and another says to use #57 with a compactor.

So I'm at the point now where I need to order stone, but have no idea what to order. Any ideas from the board??
TIA, Tom.

 

[snorvet]

most of the codes around here now say compacted ca-6. compacted ca-6 has the "fines" (very small stone, almost sand) with the stone that allows compaction. I've seen some garages years ago go with uncompacted ca-6 (without fines)

 

[larry4406]

I see your in maryland. I build houses in northern virginia.

If your slab is a slab on grade (i.e., a non-structural slab and the soil bearing capacity is good, 2500 psi or better) then my company and all of the other builders here simply use a good 4 inch plus bed of #57 blue stone, a poly vapor barrier on top, followed by the wire mesh and concrete. No stone compaction required.

All of this advise goes down hill when the soil is compromised (i.e, insufficient bearing capacity). Options here include structural slabs, removal of the bad soil and replacment with compacted certified fill($$$) or simply filling the void with #57 stone. I have built several houses where due to bad soil, the basement slab is supported by a stone bed in excess of 1.5 feet thick - no settlement issues period and the stone bed greatly improves drainage.

hope this helps

 

[mjribeiro]

I'm not sure of the number designation, but in NJ many of us use QP, quarry process - it's a mixture of 3/4 and smaller, plus stone dust. If compacted with a vibratory roller, like a 9 ton, your surface will be so hard that you can roll a 75,000lb truck over it with out leaving a dent. You will also have significant difficulty digging or driving stakes into it! (all personal experience) Add a few rains, and the stone dust locks it all together.

 

[WVBills]

Tom:

I'm in the eastern panhandle of WV and am about to embark on the same thing. Building a 24 X 24 Garage monolithic slab on grade.

At this point, I know that the building code calls for a minimum of 4 inches of crushed stone under the slab. I can't recall if the code has specs for the kind of stone but I think it does - I'll check tonight, I don't have the book with me.

My plan is to get bids from concrete guys that include 1) code compliance (it will be inspected by the county) and 2) some sort of warranty for their work.

After that, what kind of stone they choose to use is up to them.

WVBill

 

[PAToyota]

One problem you'll face asking this question is that most states designate stone by the local highway department's numbers. Here in PA what you'd want is 2B modified - which is AASHTO #57 - 3/4" and smaller including fines. Sounds like the QP that mjribeiro mentioned and the #57 you mentioned.

That is what I'd use and I would compact it. With the fines, it will sort of self compact over time, but to pour a slab on it you want it compacted first. When I poured my slab I used this and compacted it until the whole thing was as tight as a drum - 25'x25' slabs (roughly) with no expansion joints and no cracks after ten years.

 

[twostory]

I have a 44 x 26 ft slab. It took one 18 ton dump truck load of #57 gravel to cover the 1,100 sq ft area four(4) inches deep. This cost $400. So your 576 sq ft will not need a full dump truck of gravel to achieve 4 inches depth.

After I spead the gravel out and leveled it by hand. I rented a plate ******** at Home Depot and compacted it. The gravel did settle some, but the plate ******** really made the gravel fit together tightly, the surface was flat and did not cruch and move around when you walked on it (after I vibrated it).

Note: a plate ******** is the only tool that will compact gravel. A sheeps foot roller, jumping jack, etal will only move the gravel around. The vibrating plate will makes the gravel settle.

 

[stupidjet]

i'm in md. i do concrete/stonework. dont use CR-6. gravel allows transfer of water under slab without wash out. cr6 does not. gravel is self compacting, thus why you dont need to compact.

 

[SCOOTER]

Ya we call it 3/4 minus here...And like Two story said put the plate to it ..ya can't go wrong...

 

[SCOOTER]

i'm in md. i do concrete/stonework. dont use CR-6. gravel allows transfer of water under slab without wash out. cr6 does not. gravel is self compacting, thus why you dont need to compact.

Guess things get done a lil different, In different places.....

 

[Kapt]

Thanks for all the advice. I think I'll go with #57 and rent a plate compactor.