Questions for a new build

[Cdubs]

I am in the process of picking the exact location of the oven and my favorite spot seems to be right under a tree. I have trimmed it so that there will not be a branch within 5 feet of the chimney...is that enough room?

[azpizzanut]

Hi Cdubs,

Thank you for the compliment on my build.

The foundation slab is 85" x 60". It is about 4" thick but 7" thick at the edges.

The blocks at the front of the oven were temporarily placed for support while the top slab cured. Same with the 8" x 8" blocks in the middle of the base. I left those blocks in the middle. The storage area under the oven is large and they don't seem to be in the way. I store most of my wood outdoors and only enough under the oven for two or three fires. That is one benefit of living in a desert. Wood stays dry most of the year.

Cheers,

[Cdubs]

Bob,

That was a great idea. How easy was it to pull those out after the hearth dried?

[azpizzanut]

Hi Cdubs,

The front blocks were in light contact with the base. It was easy enough to wiggle them free. That speaks well for the strength of the angle iron and the filled and mortared block above since there was no downward movement after all. I could have used wooden wedges but the fit was good so I left it alone. If l had to, I could have broken one out to remove the remainder.

The blocks under the middle of the slab were in firm contact with the cement board. I'd have to break one out to remove them.

If you look at the builds of others on the forum you will see various support methods to assure integrity of the slab while pouring/curing. My top form was held in place mostly by 3 1/2" screws into pre-drilled holes in the cinder blocks. I also used lag bolts on the ends of the form lumber in addition to long screws. The vertical wooden supports were an afterthought installed while the crew mixed bags of cement. Each builder uses his own judgment and intuition regarding forms, support, and attachment methods. Most of us have little or no experience with this type of thing. What you don't want is a form slipping or bowing outwards during the pour. I could have used a wooden cross brace mid-span but felt the 2" thick lumber would hold tight and not bow. I also didn't have to edge trowel or smooth the top of the slab, but did anyway since I had the tools and time. No one can see it, but I know it is there.

Cheers,

[Cdubs]

Bob,

I never thought of screwing the form into the cinderblocks...sounds like a great way to keep everything in place. I see you used a fair amount of cladding. What did you use for that?

[azpizzanut]

The "cladding" closest to the dome is Kaolite refractory insulation, 2" thick. I applied it a handfull at a time packing it in good all around. Several bags came with the kit. The outer is perlite/Portland cement at 5:1 ratio. I used a gauge with a center-pin to measure the thickness of the perlite mix as I went along.

Cheers,

[Neil2]

"I also didn't have to edge trowel "

It is always a good idea to edge trowel any slab. If you don't, the initial slight curing shrinkage will leave you with a slight "dish" edge which may end up being a water trap.

[Cdubs]

can someone explain what "edge trowel" means and how I go about doing it?

[azpizzanut]

Hi Neil2,

Yes, you're right. A slight dish will appear at the edge of the slab from shrinkage, and sure enough, it does catch a little water. However, my slab is fully enclosed and tiled at the front, none of it is exposed to rain. Edging it was just exercise.

For those builders that place concrete for structural or decorative elements of their ovens or outdoor kitchens edge troweling is a must if it will be exposed. Newbies might be tempted to begin working the cement before it is ready, and if it is started a little bit too late, then it is difficult to work the stones down and retain a smooth edge. When done at the right time the finished product is a thing of beauty, very satisfying. It gives a very "finished" look to the job. An oven sized slab is easy, a patio or driveway is a lot more work if done on hands and knees though. Get the right tool for the job and you'll be a pro in no time at all.

Cdubs, Neil2 posted a picture of an edge trowel, above. They also come with wooden handles and are not expensive. I've had mine for years. Clean it up and take care of it when you're done and it will always be ready when you are. Same as for any tool.

Cheers,

[Neil2]

I suggest using the edge trowel right after pouring and floating / leveling the concrete. Use lightly, just enough to "push" the larger aggregate particles in away from the edge.

Use it again lightly after about 1/2 hour and once more when doing the final finishing after skim over.

Its actually even easier than it sounds and gives your work a nice "professional" touch. They are relatively small tools, about 6 inches long and 3 inches wide and will run $7 to $10, and as Bob says, if cleaned and put away will last forever.

If you live in an urban area, take a look at the sidewalk in front of your house. An edge trowel was almost certainly used and that is what produces the rolled edge and border effect.