Prep/Site Work for Slab

[tinmanwpk]

In preparation for a new garage slab I have a stump about 36" diameter right where i want my slab. Can I burn it down to 12" - 18" below grade and have the site prepped with the remainder of the stump in place, or should I have a backhoe just tear it all out?

 

[Beemer]

If it were mine I would get rid of it and replace with gravel thoroughly compacted in 8" layers or alternately use very small sized crushed stone, not round stones.
Don't just push the soil back in the hole because it will be loose and will settle when it gets loaded.
Organic material left in there will eventually make you unhappy.
I once had a contractor, who knew better, ask to leave a tree stump in where a restaurant foundation was going. I was embarrassed for him.

 

[tinmanwpk]

I figured that was the case, I just needed some confirmation. I hadn't figured the 8" layers, so I also appreciate that tidbit.

 

[u2slow]

My site was a nightmare that way. The more he dug, the more stumps and junk he found. (A ravine was hastily bulldozed over some 40 years prior).

After exacavation, fill was brought in, and compacted in layers. It did save me in concrete at the end... but that fill and machine time was expensive.

Build on top on that organic material and you'll get foundation problems (sinking and shifting) down the road.

 

[tinmanwpk]

Here we go!

GJ Concrete Slab thread

 

[kbs2244]

most codes do not allow organic stuff under a slab
it will rot and leave a void

 

[Beemer]

I figured that was the case, I just needed some confirmation. I hadn't figured the 8" layers, so I also appreciate that tidbit.

That is the commercial standard that you won't regret. Much thicker than than and it's not going to be thoroughly compacted.
There is a big difference between commercial and residential knowledge and practices. That is the main reason my liability insurer didn't allow me to do residential design unless they boosted the rates significantly; too much risk.

My former architectural client used to respond to contractors who would say "we've always done it that way and never had a problem" by responding "that doesn't make it right".

 

[tinmanwpk]

As far as commercial standard, this is better than good. I am building a small garage next to my 10,000 sq. ft. fabrication shop. I'm sure somewhere down the line the garage will be removed but we can repurpose the slab and incorporate it into a new addition. We will have forklifts and heavy equipment, so we need a more robust slab.