What to use under slab?

["Jacob Robinson"]

The place where my proposes 30x48 building is going to go is not the most level spot.

The land drops about 22" on the 30ft run and since I don't want one side below grade what material should I use to build up under the slab?

I also wnat to go the cheapest way possible even if it is more labor intensive, since I work for myself for free

aslo what type of concrete works the best

Fiber or
no fiber with wire mesh

[Karl Brogger]

What type of building are you doing? Pole, something with a foundation, or slab on grade with the slab being thicker at the edges acting as the footing?

[Scott Loven]

I would remove the sod and soil and fill in with rock. You could also use compacted sub soil.

[Scott Wigginton]

I used fiber for my small addition, it is only $7/yd extra (in Virginia anyway) and your job looks to be about 20 yards so it would only cost $150 whereas remesh would be $300 (2 rolls of 150' x 5') plus the effort of installation.

If you were to just fill it up to the new grade (22" on the backside) it looks to be about 40-50 yards of material (or 60-75 tons with WAG 1.5tons per yard). I can't attest to what fill materials are appropriate or how thick you can go with each, but I know fill sand in my area is about half the price of crush n run.

[David G Baker]

Sand will work well, or a mixture of sand over rock. Make sure that the sand is encapsulated so it can't wash out. Something else you might think about if you live in cold country is put 2 inch foam board insulation under your slab, it really helps keep the cold at bay and helps prevent condensation from forming on your slab.

[Travis Rassat]

I don't know what kind of timeline you've got, but with that much fill needed I'd also let it settle for a year before pouring the concrete and building. Otherwise, you might have a lot of cracking.

[Scott Wigginton]

Something else you might think about if you live in cold country is put 2 inch foam board insulation under your slab, it really helps keep the cold at bay and helps prevent condensation from forming on your slab.

Second the insulation (can't believe I forgot!). Depending on your use & budget you could also throw in radiant floor heating.

[Von Bickley]

Jacob,

Around central SC, we used "Sand Clay". It will compact super good. It is also what the pole buildings use to build up a site. It is also used to backfill porches, carports, and backfill around houses.:)

[Steve Clardy]

Around here they use what they call ....Dirty fill...

Which is a mixture of clay, white rock, and lime grindings. Stuff that cannot be cleaned up from processing and grinding up white rock from quarries.

Its used on fills and on the edges [shoulder] of the roads around here. It packs down real well.

[Matt Ellis]

Around here they use what they call ....Dirty fill...

Which is a mixture of clay, white rock, and lime grindings. Stuff that cannot be cleaned up from processing and grinding up white rock from quarries.

Its used on fills and on the edges [shoulder] of the roads around here. It packs down real well.

we call it "crusher run" around here. we specify either that or #57 stone under all our slabs on grade for commercial buildings. it should work fine for your residential slab.

make sure it is tamped/compacted properly, and that you place your vapor retarder between it and your slab.

-matt

edit: i just read the rest of the post about fiber vs. welded wire reinforcing. fiber DOES NOT provide primary reinfocing for the slab. it is a secondary reinforcing intended only to help control some of the surface shrinkage cracking as the concrete cures. in my opinion, you should do both...something like a 6x6 - W1.4/W.14 (10 gauge) should work just fine for you. also, remember to have your shrinkage control joints cut while the concrete is still green.

[David G Baker]

Travis,
From the research that I have done, if the slab is poured over existing settled ground and sand is added as fill, the sand will not settle. It needs to be compacted some prior to pouring the slab but that is pretty much all that is needed. This is what was done under my 30'x40' pole barn 6 years ago and so far no cracks. I had 18 inches of sand fill.

[Jim Becker]

You not only need to deal with the build up using a compactable material, but you also need to remove the top-soil from the entire slab area to insure you have a stable subsurface. The same compactable material can be used to fill back up to your intended grade. While there is a cost involved, this kind of prep work insures that your slab will be as stable as it can be over time. Usually this fill is made up of a variety of sized particles that interlock when you run the compactor over it. (I don't know what the stuff is officially called...)

[Ken Fitzgerald]

What ever fill you use.....put it down......water the daylights out of it and then compact it. Wait a few weeks for it to dry. Water it some more and then compact it again. The watering and compacting it while it's wet generally makes for a solid foundation in my experience.

[Matt Ocel]

You do need to remove all top soil, anything organic must be excavated out. Call your local quarry to get recomondations and pricing on "fill". Keep in mind "fill" can be quite different in structure and pricing. Ask for the Delivered cost.
If you are going to do the concrete yourself and are not familliar with mix types, you can once again contact your local ready mix company to get there recomendations for what is best in your area.

[Don Bullock]

As one who just had a building constructed, I'll tell you from experience that you need to check the current building code for your area for foundation requirements. Sometimes even the contractors and builders aren't as up-to-date as they say they are. The local building code may dictate what you need to do for your foundation.

[Thomas Pender]

I agree with removing the top soil, compaction, no organics, figuring out the code, etc. (Oh - I saw no mention of excavating below the frost line, if applicable.) One thing I would recommend is hiring a professional Civil Engineer to scope out the ground and design the foundation based upon the expected load. After many years of construction litigation, I can tell you that one of the most litigated area is dirt and what it does to concrete - including drilled piers (like for decks), footings, grade beams, etc. You can get lucky and just place 4" of concrete (with rebars on high chairs) over compacted subsurface soil and rock or you can get unlucky - fast and expensive. But, no sensible builder "wings" concrete design - the results are final and expensive.

Obviously, if you have a sandy soil without clay, some gravel and concrete will work fine. But, if you have an expansive clay soil and some clay soils, like in Texas, Lousiana, Virginia, Georgia, etc., can generate more expansive force than dried concrete when made wet, you have to get that clay away from your footings or slab and perhaps excavate for several feet out beyond your margins and then make sure wet does not get into the subsoil.

Best case - a few feet (or less) of dirt over a rock formation (which cannot expand or move) or sand. I hate to recommend someone spend money, but it could save you in the long run. (Good drawings are also nice.)

If I had my druthers, I would use post and beam over a compacted fill or gravel and use post tensioning to tie it together.

Where the land drops (as you mentioned) you will need to build a CMU wall (a designed and reinforced one is safer and better) to retain the fill. You can build up walls with block on top of footings or rock and then fill it in until it is level (it will have to be compacted). Whether mesh will work or not depends on the thickness of the concrete and how much compressive strength you will need. I prefer #4 rebar tied together in squares resting on high chairs. Regardless, I keep coming back to getting some professional help in the design.

Good luck!! -- Oh - Do you know what an elephant is?

Answer: A mouse designed by a Professional Engineer.

[Gary Lange]

I wouldn't build it without a properly constructed foundation. Everything you do the right way now will mean less headaches later. Like everyone says check the code for your area and then have a footing and foundation constructed and filled for the floor.

[Matt Ocel]

Let me digress(is that the correct word:confused:).

You have to follow basic construction methods, and local building codes.

ie. frost footings, make sure footings are on virgin soil, size of footings.

Most of these items are boiler plate stuff for your area.

The advice some are specifing may work in there part of town but not nessicarily in your part of town. You may be over building or under building.

Go in and talk with your local building official, they will help you, thats what you pay taxes for.

If your going to build a post type building, then I may have just wasted a lot of ink.

[Greg Cuetara]

Good luck!! -- Oh - Do you know what an elephant is?

Answer: A mouse designed by a Professional Engineer.

hey now...no picking on us engineers.....that elephant must look like a mouse :D

btw back on topic...take Matt's advice and go talk to the building official. I would suggest that you give my profession some money and hire a civil engineer but that may not be in your budget. If you can find a local engineer one man shop you may be able to get some good advice for minimal expense which would be the ideal solution.

Good Luck,
Greg