Slab thickness Getting Started Discuss Slab thickness in the Pizza Oven Design and Installation forums; I spoke with a vendor at the Arlington Texas Garden Show today about building a WFO who claimed to be ...

[PlanoPhil]

I spoke with a vendor at the Arlington Texas Garden Show today about building a WFO who claimed to be a master mason and he told me that I should make my foundation slab atleast 12 inches thick. Is he all wet or just trying to discourage me from building my own WFO? He was trying to sell me a $3500 prefab oven that he claimed I would be making pizza in 2/3 hours after he started the build.

Phil

[Les]

Phil - that seems a little thick to me. Mine is only 3.5 inches except for the perimeter footings. Maybe he builds a lot of airport runways.

Les...

[Neil2]

A layer of gravel so it doesn't get contaminated by fines and 3 1/2 to 4 inches should be fine. Use lots of rebar: 3/8 on 8 inch centers both ways bent at the ends.

[Tscarborough]

Mine is 4" with one #3x20' rebar cut into 5 peices laid in around the perimeter and across the center. I mixed the mud from scratch with some free sample masonry cement, gravel, and sand. By my calculations, I needed the slab to be at least 300psi (approximately equivalent to packed Dirt), and I figure I hit at least 2000. My advice is to overbuild as much as you can afford, but in Plano, 12" sounds pretty extreme.

[dmun]

Just for the record, a twelve inch thick footing on undisturbed soil, below the frost line, protruding six inches beyond the perimeter of the structure, is code for masonry fireplaces. That said, almost no one builds freestanding ovens this way. If it's part of your house, and you need to design to building code, then fine. Otherwise, a 3.5 inch slab on well drained crushed rock is all you need.

[Millstone Man]

Phil - dmun is right. You don't need the 12'' slab but I would put piers under it down as far as you can dig (check out Fairview WFO on this). Our soil is unstable and very susceptible to movement. I'm in the final planning phase and will be putting in piers soon. - Scott

[PlanoPhil]

Scott - By piers do you mean concrete using those round forms available at HD? What diameter, and how many? Or do you mean a footing (trench) around the perimeter that is 12 inches or so deep?

Phil

[dmun]

>>>personal opinion alert<<<
I think putting random sonotubes under your slab is the worst of both worlds from a frost heave perspective. Without flared footings at the bottom of your pillars, it just gives the ice lenses something to grab on to.



I say, either build proper footings below the frost line, or pour a reinforced slab on well drained crushed rock. Don't do a bit of both.

[Tscarborough]

Plano does not have a frost line, just black gumbo mud.

[Millstone Man]

Frost line is not an issue but the black gumbo is a pain. Dig with a post hole digger or a bucket auger (Elliot's Hardware) down at least 3 feet on the corners. Put a layer of sand about 3 1/2 to 4 inches thick under the 3 1/2'' slab to take care of the shrink and heave gumbo issue. Think of it as building a table with legs where the table top is your slab and the piers are the legs and the sand allows our soil to move without affecting your slab. I just bought a bucket auger I can loan you. Contact me at scottk22@mac.com.