Another foundation question

[gjbingham]

You're definitely a builder! Everything looks great, even overdone a bit. That's good. Removes the chances for errors. Nice pics too. Keep up the good work!

[biondoli]

Mfiore,
I had the same dilemma you are going through...I am in Minnesota and our frost line is 48" I think. My oven is built on a brick patio, I should say that I built the patio in order to build the oven, but anyway...I had 2 choices: build 4 concrete pillars below frost line and on top build the base slab for the oven, just like a first floor of any building. All of this seemed too complicated and cumbersome to me, and after speaking with a friend who build the oven on a floating foundation in the middle of woods 10 years ago and it is still there without any crack...I decided to take the risk; the foundation of the brick patio goes down 2-3 feet with packed sand and gravel which keeps the water away. So I decided to take the risk. You need to consider the place you are building the foundation, if it is stable, if it is a place where water stands or it is a place where water runs during big rain...all of these factors will play against the stability of the terrain. On the other end, garages are built on floating concrete with no re-bars. So if you want to be 100% sure go with the pillars or something similar, if you think you can take the risk, my only suggestion would be to build a solid slab (more re-bars) and ticker (6-8") and even if it moves, will not brake, so all the structure will move a little bit and it should not be a problem. Hope this help, Carlo

[sharp21]

Originally Posted by dmun

Here's a quote from the last link, the Canadian Building Digest:
Where a detached building is located on a concrete slab on grade, protection will be provided by placing the slab on a mat of coarse granular material, which will act as a buffer against any movement of the soil under the mat. A mat 12 to 18 in. in thickness is usually adequate

Would you compact sand on top of this layer for levelling purposes, before putting your slab down?
S.

[biondoli]

If the gravel is well compacted then I would not, as you can level with the concrete pour (for the slab)

[sharp21]

I actually have a 6'x8' slab that I am going to put down, instead of pouring one.
Should have clarified
S.

[biondoli]

then I would add the sand otherwise I don't see how you can level it, on top the sand will help to distribute evenly the weight

[sharp21]

Thats what I thought, just wanted to double check
Thanks!
S.

[SpringJim]

Okay guys, if I have a natural sand base on higher ground, do I need anything under my slab?

I think when the garage nearby was poured it was just done on the sand.