Need some opinions on putting in a slab for a building

[Bricklayer51]

Will the building be sitting on the slab, or the slab on the inside of the walls?

[Jeff]

I've not determined the method of construction yet. I just know when the time comes that I'm at the point I'm able to do swing it, I want the site prepared before hand as much as possible.  For now, that means the trees and stumps gone and possibly the grade set. My main focus is taking care of these things when the possibility of oak wilt infection is at the very lowest. I have predominantly oaks here and would not want to see them wiped out.

[scsmith42]

Jeff, I am a contractor by trade and I recommend that you NEVER leave any organic matter under a foundation. Anything organic under your slab will not be preserved but will rot and cause you problems. Also the "fiber" used by most concrete batch plants is not rated to replace remesh wire. Google "Strux 90/40". It is the only fiber that I am aware of that can replace wire in a foundation. In the grand scheme of things it wouldn't cost much more to do wire and Strux 90/40. Here in Mississippi the Strux 90/40 costs about $8 per yard more than the worthless cheap fiber mixes. Just my opinion but if it is worth doing it is worth spending a little extra to get it right the first time.

^^^^ I concur about organic matter removal (stumps, topsoil, roots) and not depending upon fiber to replace metal reinforcement. Would also recommend mechanical grade compaction and a low slump concrete mix when you pour...

[Jeff]

Not to much worry about top soil here. The only top soil to speak of gets brought in.

[Stephen Alford]

  The general practice here is if there is a source of good shale it's dug out then the stumps and organics go in that hole , the good shale is placed and compacted where the slab for the structure is to go.   In recent years there are  more weather events were water is running on top of the surface, so the slab site is always elevated. 
  The new idea (at least to me) when its used as a "shop " pertains to heating it.  Trenches are dug and non perforated drain pipe is laid. Plastic drums go on the far end of the pipe.  Fans are put in the drums and blow air through the pipes that come up in the shop.  As I understand it this will keep the shop temp at around 7 c.   Good luck with your project,looking forward to pics.   

[BEEMERS]

Ive done home sites,garage slab preps by the hundreds in this area..we'll get it right..especially if you let it sit for awhile and get a few good rains.Plus roots in your area don't go to deep theres nothing good to get into down below so they tend to stay closer to surface..which spreads oakwilt further,given a greater chance of grafting.
that being said will keep depth of disturbance minimal.
25 years of this and ONE problem...had a basement and attached garage job while I was backfilling basement  I told the Block layer/concrete guy that Id lay the fill in for free because I was already there.He directed me and I dribbled the sand in with an excavator as he needed..then he and his
laborer knocked it down and compacted it in lifts less than 12"
the fill was perfectly compactable sand but it was really dry and told him several times that I didn't like it and it needed water..it was almost dust.well was dusty.They did what looked like a perfect job.What do I know right? Im the dirt guy and they are the concrete guys...any way a year later the slab settled 6 inches against the basement wall and the rest was a mess.
All I did was dribble sand in as directed..for free...and argued that they needed some water with compaction,so why a problem for me?They said that I compacted it!!! I about crapped but a few threats to life and all was well..they tore it out.And replaced it.
Sorry bout the rant..Hey Brucer..I liked your post..there is a couple subdivisions here around Cranberry lake..little lots,little cabins built in the 60,s .They buried all the stumps from each lot right in the front by the road on each lot!All my life Ive been filling them in and I mean some you fill in and come back a few  years and it settled more and fill it again.I mean some are 3 foot deep.
Every year we get calls to haul fill and if it goes to Cranberry lake subs that's probably what its for...I make it real clear to my guys..reguardless of what the home owner says..do not drive through the hole..if they want to fill the hole..back up TO it and dump.Back up IN it and youll be sitting on the frame....yes I know from experience

[Reddog]

Jeff, let me throw out another option for a surface.

How about using 3/4" crushed lime stone with fines. Put 3" deep or more depending on budget.
Put a perimeter of pressure treated around the outside to confine the material.
Then water and plate compact. turns to a poormans slab after a few rains.

[Corley5]

A neighbor put "slabs" in a couple out buildings by spreading a layer of Portland cement, working it in with his rototiller and then soaking it with a sprinkler.  It made a hard surface  :-\

[barbender]

Beemer, I don't mean to say that water shouldn't be used. Just that it shouldn't be relied on for the sole means of compaction. But Beemer is right, dry sand will not compact. On our crew, we used class 5 gravel for most everything. It's easier to compact correctly, but then the company I worked for owner all the travel pits too. If I am putting in a slab base for myself, I'd use gravel except forf the last less than 1" of grade. That's just so I can screed the grade off after compacting the gravel. On the fiber issue, there are different fibers that can be added that add different strengths. For the most part, they add crack resistance (for small cracks) and they can also help keep outdoor concrete from spalting. Steel mesh also only helps with crack resistance, it doesn't add any actual strength to the slab. If you were to try spanning stumps, you better add rebar. That's what gives concrete the ability to span any distance.

[Planman1954]

Be sure to use concrete wire mesh (6x6x10/10). One fellow said it does no good, since many finishers let it lie flat. He is right. But the solution is to always use clip chairs. These elevate the mesh to the center of the 4" concrete, and all is well! Put the mesh in. ;D

[Rockn H]

A neighbor put "slabs" in a couple out buildings by spreading a layer of Portland cement, working it in with his rototiller and then soaking it with a sprinkler.  It made a hard surface  :-\

Soil Cement, the poor man's shop floor:)   I've even see the military use it alone for runways.