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.