Red Clay...

[USAFpj]

... is holding every piece of moisture it can get it's hands on.

My grader did a superb job of clearing and leveling, but it rains hard for a day, then sunshine for 4, then rains hard again. If it would just dry out for a solid week, I think he could lay down the crusher run and get this pole barn built. Then wait for it to fully dry out before the concrete is poured.

I still have large puddles from when it rained 4 days ago...

 

[pmiranda]

Nasty stuff... doesn't drain, swells with rain, shrinks with drought.
Don't you need some soil treatment to build on that? Or do the poles go below it to something more stable and you're letting the slab float?

 

[USAFpj]

Poles go below the clay, and posts are placed on crete cookies. It's not the best of material, but barns have been built around here for hundreds of years, so I'm sure the companies and crete guys have a bit of a clue on this... hopefully...

 

[pmiranda]

Cool. rebar?

 

[USAFpj]

No rebar. 4in of 3,000psi fiber. I understood rebar to be common sense, but did a lot of research, and with the help of a lot of knowledgeable guys here on GJ and their private messages, feel confident if the base is compacted extremely well, and saw joints are cut in a timely manner, rebar is not needed.

Time will tell.

 

[pmiranda]

I just figured with expansive soil like that you'd need rebar. Alot of people on here don't live in clay country, but if you aren't planning on a 2-post lift it should be no problem. And of course local knowledge is king.

 

[USAFpj]

P, let me ask you- if the 2 post manufacturer only requires a minimum of 3.5 or 4in slab, and ensuring that it is indeed 4in throughout, where is the need for rebar or increased thickness or psi?

Local knowledge (the builder) says that for where ever you want your post, they dig deeper in that specific area and pour a large footer under each post. I'm not sold on that, either.

 

[1953mercury]

What ever else you do, insure that your site is grade to carry ALL water away from the building. Mike

 

[My Old Tools]

We have black clay here. We definitely use rebar in slabs, in fact the smart ones go up a size on the rebar.

 

[chops101]

At a minimum I would use wire mesh. It's cheap.
My Dad had a driveway poured in Catawba County (NC, red clay like you have), the concrete guy buffed at the notion of adding anything. I wish I would have stepped in with some logic.
Driveway cracked like a mofo after a few years.

 

[ddawg16]

Your only solution is to scrape away about 2' and bring in top soil

I don't miss the stuff........I swear, if your engine ran out of oil, you could use red clay

 

[pmiranda]

Dunno how much crusher run is going in, but that should stabilize it a bit. I know my driveway is concrete on black clay with expansion joints separating it into 4 big panels. One of the panels (highest point) is a couple inches lower than the others after about 10 years. Probably no real prep went under it but it's got wire mesh and/or thin rerod and all the panels are intact... just different levels.
I have no experience with fiber reinforcement... might be the bees knees, but for a 2-post lift I'd want at least 2 feet around the posts and the part between them to have rebar and be thicker than 4". That way when the rest of the pad cracks off at the control joints the posts will still be stable and plumb.
Definitely want to have controlled grading around the building but the name of the game is stability, which means watching the soil moisture and (in my drought-prone area) watering the foundation to keep it steady.
For my new shop build I'm thinking of sinking pvc 4' deep into multiple test sites around the building so I can go around every week or two and check the moisture with a probe. Or if they're cheap enough, just install probes permanently and run them to a data logger.

 

[USAFpj]

Thanks for your input, gents. As of now, we're doing 4in of compacted crusher.

 

[ishiboo]

4in of crusher and no rebar sounds like a recipe for slab cracking.

I have a ton of red clay as well. The parts of my property I don't need to build on, I can dig down a foot and find gravel. But wherever I want to build is just about solid red clay. As you said, stuff has been built on it forever.

As we understand building materials more and more, and have more and more experience to show what works, I would definitely use rebar on the slab and a deeper base.

 

[machsnell]

Rebar is such cheap insurance it is foolish not to put down especially if you have clay. One way to find out if you needed it.

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[brownbagg]

mix some cement with the clay, it be dry and hard within hours