Foundation questions

[chickade]

I visited a Forno Bravo dealer today, was impressed with the product, and am ready to forge ahead with the project. However, the foundation remains a significant obstacle. Since I am new to most construction (I built a chicken coop- that's it) I don't really even know what to tell a contractor about the job.

I have selected a site, obtained a permit, and hired a concrete contractor, explained my requirements, however, it appears that he spread a large variety of gravel over the existing area without digging it out, and didn't use a compactor.

I have since read that digging below the frost line is important in installing a concrete slab.

Do I start from scratch- remove the gravel, dig down 24 inches (I live in Pennsylvania) and then re-gravel and compact the gravel? Is it important to use pea gravel as mentioned in the Pompeii oven plans?

Another question is whether the pad can be larger than the oven foundation- I was planning to make mine 9 x 11 so as to have extra room for counter space, but now I'm concerned that the weight differential (under the oven versus under the counter) will make the pad prone to cracking. Should I play it safe and just make the pad the recommended size in the Pompeii plans?

Also, I have read that there are some concrete additives that make the mixture much less prone to cracking in cold weather. Should I look into that?

So many questions.

Thanks for your help.

[irelande5]

Re: Foundation questions

Hi, Like anything, you are going to get different opinions about this. I researched this a lot (live in Ohio), tossed back and forth between having a footer, or going with a floating slab. Most state if you put in a footer, your slab will not move, therefore your pizza oven/foundation will not move, I believe this to be true myself. This is very expensive, digging below frost line, a lot more concrete, ect, but it is piece of mind.

I dug out around 1' below, and added 6" of compacted gravel, then poured a floating slab on that, 6" re-enforced with lots of rebar. After talking back and forth with Mingy (forum guru) and other folks, I decided to go this route, he bascially stated if it heaves and lowers with frost, typically it is universal on the slab. Regardless, by installing 6" gravel, insuring I have a good drainage pitch, I feel relatively confident that I wont have any issues. I did the work myself, and time/material, just didnt have the energy to dig down 3ft, however if I had the money, and a contractor, what not put it on footers to be sure?

You want to use a gravel that will take the weight and drain, compacted dravel (skeet) is best IMO.

Pour your pad as large as you want for extra room, just insure contractor installs expansion joints were needed. It will not make it prone to cracking IMO.

Not sure about additives, sometimes adding fiberglass strands help, but concrete is going to crack.

[Mingy]

Re: Foundation questions

"it appears that he spread a large variety of gravel over the existing area without digging it out, and didn't use a compactor."

This is a big no no and you should stop him. You always have to remove the topsoil down to undisturbed ground. The danger of not compacting is that the slab (see below) might tilt or shift. This would be bad.

"I have since read that digging below the frost line is important in installing a concrete slab."

That is absolutely not true unless you are going to tie your oven to an existing structure. I am from Canada and it gets cold here and there are plenty buildings built with just a slab. It is true the building may rise a tad and sink back down but this would only be an issue if it were connected to something which doesn't move up and down. I have a large garage built on a slab and there is no problem. A foundation would be an expensive waste of money.


"Do I start from scratch- remove the gravel, dig down 24 inches (I live in Pennsylvania) and then re-gravel and compact the gravel? Is it important to use pea gravel as mentioned in the Pompeii oven plans?"

You have to remove the gravel and dig to below the topsoil. I always install a geotextile before I place the gravel. I don't know about pea gravel - it doesn't compact very well but it drains well. I just use 3/4" crusher run and compact it.

"Another question is whether the pad can be larger than the oven foundation- I was planning to make mine 9 x 11 so as to have extra room for counter space, but now I'm concerned that the weight differential (under the oven versus under the counter) will make the pad prone to cracking. Should I play it safe and just make the pad the recommended size in the Pompeii plans?"

Can can make it as big as you want. Concrete always cracks but that won't be a major problem if you add enough rebar and reinforcing mesh (the 6x6 stuff) because the slab will act as a single solid piece. Think of it this way: a proper slab won't fail because the weight of the walls is different from the weight between the walls, at least if the site is well prepared and the slab properly reinforced.

"Also, I have read that there are some concrete additives that make the mixture much less prone to cracking in cold weather. Should I look into that?"

Concrete cracks because of the stresses associated with curing and differential weight loads. If you properly reinforce, those cracks will remain tiny, or nearly invisible. I have heard about fibers additive but never used them. I use rebar and steel mesh. There are chemical additives so you can pour in the cold, but its best not to pour when it is too cold.
There are things like fiberglass,