Slab On Grade.. More Opinions Than Carter's Got Liver Pills

The more I read about concrete slabs the more I realize it's more art than science.

My barn is done and they'll be prepping the interior for the slab, with any luck, next week.

During my attempt to research "the optimal slab design" I have unearthed:

• Re-bar vs. Wire Mesh vs Fiber Mesh vs Wire Mesh and Fiber Mesh,
  
• Re-bar assures additional cracking vs always use re-bar,
  
• Plastic Chairs vs Wire Chairs vs Concrete Chairs,
  
• Thicker concrete at high load areas (2 post lift) vs a uniform area throughout,
  
• 3,000 psi vs 3,500 psi vs 4,000 psi,
  
• Vapor Barrier vs No Vapor Barrier,
  
• Always ask for mix sheets vs you don't know how the hell to read them anyway.
  
• And my favorite: That link is 10 years old... that's not good information!

In any event I have amassed quite a number of links and figured I would share them here.


Selecting Sub Grade Materials: Soil Compaction Handbook

Visual Inspection of Concrete

Better Garage Floors

Flatness:
http://www.concreteconstruction.net/how-to/floor-flatness-number-conversion_o
http://www.faceco.com/docs/40 Questions June 2012.pdf

Slabs On Grade:
http://www.bpesol.com/bachphuong/media/images/book/3021r_96.pdf
http://www.constructionknowledge.net/concrete/concrete_basics.php


Plastic Crack Risk Calculator: https://plasticcracks.siue.edu/index.php?unit=Standard&zip=45339

Vapor Barriers: http://www.stegoindustries.com/docs/Vapor Barriers Under Concrete Slabs.pdf

Building Tips for Trouble-Free Slabs: http://www.cement.org/for-concrete-...truction/building-tips-for-trouble-free-slabs

International Building Code Section 1803: http://www.ibc-wiki.com/section-1803/

Cold Weather Concreting: http://www.concretenetwork.com/cold-weather-concrete/curing.html

Control Joints:
http://www.concretenetwork.com/concrete/slabs/controljoints.htm
https://inspectapedia.com/structure/Concrete_Control_Joints.php

Wire Mesh Standard Practice: http://files.engineering.com/getfil...c=212727627.1.1460754610957&__hsfp=2088101374

Effect Of Rust On Bond of welded Wire Fabric http://rebar.ecn.purdue.edu/wwr/Library\Effect of Rust on Bond of Welded Wire Fabric.pdf

Re-bar Spacing a/ Weight & Materials Calculator: http://www.blocklayer.com/rebar-slabeng.aspx

Concrete Cracking Overview: http://www.cfawalls.org/foundations/cracking.htm

Concrete Floor Slabs On Grade Subjected To Heavy Loads: http://www.constructionknowledge.ne...ts/Div_3_Concrete/Concrete_slabs_UFC_2005.pdf

I read every concrete book in Cinci public library about 30 yrs ago. 5 of them relating to pre cast pre stress and post tension. Wish I would have had a refresher last big job I did. Still made my share of mistakes.

One of the biggest factors is sub-base prep. If the sub-base isn't prepped well you won't have a good result. Proper material and compaction are key. Inconsistent compaction and you will have cracks and shifting. I seen floors with nice rebar mats tied in them look like jigsaw puzzles and unreinforced slabs placed on good sub-base without so much as a hairline crack.

Steel requirement depend on the loads to be placed on the slab. Lots of heavy stuff or things that will impart resonant or vibratory loads have higher requirements than a slab for your daily driver. Welded wire mesh for a car barn may be fine and a rebar mat for a truck shop. Need dictates.

This is what happens when an engineer starts to think about his own projects. The research is overwhelming and frequently contradictory.

I won't tell you what the best way to do it is, but I'll tell you what has worked for me, not only on my own projects but for others as well (as a paid engineering consultant).

First, the absolute A-number-one best way to insure that your slab is going to be of high quality, is to make sure that your subgrade is perfect. Flat, solid, and compacted to as close to 100% of maximum dry density as possible. I did my house basement slab, a shed and my new garage all the same - compacted the base, let it overwinter, compacted again, leveled out the high and low spots and compacted a third time. I also used crushed stone underneath each one. 12" for the house, over native soil, 6" under my shed slab, and 36-48" under the garage slab (hey it was cheaper than gravel at the time). If you think it's been beaten down enough - do it once more.

Have an expert design your concrete mix and have an expert crew place and finish it.

In all of my slabs I used 6x6 welded wire mesh. The house and shed used 10 gauge, the garage has 6 gauge. Should I have used rebar instead? Maybe. It might have been easier to walk around on it and finish it, but it was a LOT more expensive. My garage slab is a full 6" with fiber as well, and all of the mesh was set on Lotel Mesh-Ups plastic chairs.

Thicken the concrete at lift points. At least a 4' square, 12" thick. Reinforce with rebar. This is where the expert is useful to design the footing for the point loading.

Vapor barrier? Yes. Insulation? Yes. 4000 psi mix? I did. Your mileage may vary. I wouldn't go less than 3000 and if you don't specify what you want, you can get anywhere from 1800 to 3000 psi mix depending on the supplier. 1800 is basically flowable fill.

I also should add that I refused to put control joints in my slabs. Ten years on the house slab and I did find a single hairline crack, and I mean tiny. Also one hairline crack in the shed. Concrete cracks, it's unavoidable, you can (usually) control most of it, or you can make sure your base is bulletproof, reinforce the hell out of it, hope for the best and live with what you get. If you do everything right it won't be an issue.