[Willie T]

Answer...

I'm doing a uni-pour on an 11' X 21' garage addition and have some questions on the prep work.
1. On the floor area inside the footings do I need to remove the sod prior to adding the crushed stone base? YES. Can I just weed eat the grass down to bare dirt or do the roots need to come out? NO. Get at least most of the weed root out that you can.

2. It requires 4" minimum of crushed stone base but with the slope of the yard can I put in up to 12" of crushed stone (compacked) with out any problems? It would save on concete. NO. Not if this is being done to save on concrete. Pour all the concrete depth called for.

3. I will need a form wall to hold back the crushed stone from falling into the footings and I plan on using 2 X material. Is it recommended to remove this form prior to pouring concrete or can i just leave it and pour the concrete with the boards still there (encasing the boards in the concete floor)? NO. You want nothing in the ground that will decay and leave cavities behind. This is one of the reasons for all the compacting.
Thanks in advance.

 

[Jim Hart]

Thanks for the advise Willie T. If I add 12" of crushed rock my concrete slab will still be 6" thick and only 3 1/2" of concrete is required. If I only put in 4" of crushed rock I'm going to have a 14" thick concrete slab. I have 18" from the top elevation of my new floor to grade that I need to fill. Comments?

 

[jomama45]

I'm doing a uni-pour on an 11' X 21' garage addition and have some questions on the prep work.
1. On the floor area inside the footings do I need to remove the sod prior to adding the crushed stone base? Can I just weed eat the grass down to bare dirt or do the roots need to come out?
Not only remove all of the sod, but also remove all topsoil & any other organic matter.
2. It requires 4" minimum of crushed stone base but with the slope of the yard can I put in up to 12" of crushed stone (compacked) with out any problems? It would save on concete.
You can definatly add gravel to bring up the entire interior portion of floor to 4" thick. No benefit in pouring the slab in varying thickness due to grade. Just dont cheat on the minimum thickened edge depth or re-enforcement.
3. I will need a form wall to hold back the crushed stone from falling into the footings and I plan on using 2 X material. Is it recommended to remove this form prior to pouring concrete or can i just leave it and pour the concrete with the boards still there (encasing the boards in the concete floor)?
I've replaced a few slabs with thickened edges thru the years that still had the wood buried in them. As a matter of fact, I cant believe all of the wood stakes, etc... we find under old concrete pours, & how good of shape it's still in, considering it's been buried for 30-50 years. Still, we rarely set anything up to hold the gravel back, as it can easily be compacted at a 45 degree angle. The few times we set anything up to restrain the gravel, we used chicken wire & rebar pounded into the ground. But note, you need to install at about a 45 degree angle, not straight up & down, to achieve slab integrity.
Thanks in advance.

Good luck! :thumbup:

 

[Jim Hart]

Jomama, great suggestion on the chicken wire and the 45 degree angle. I think I'm headed in the right direction now.

 

[Willie T]

One comment on the crushed rock compacting. It provides a better base for the slab if you spread progressively finer and finer layers as you come upward (compacting between each layer) of rock in the thicker areas. Crushed rock really does not compact all that well if it is too big.