Oven in Virginia

[Neil2]

"Just run your skill saw through the blocks, knock out the tabs,"

You can get the blocks already made with the knock out tabs. The tabs then fill/block the bottom of the cell so you pour concrete in. Ask at the yard for them.

[Neil2]

"I tend to dwell on the imperfections long after I've moved onto the next phase"

Its a pizza oven, not a Saturn rocket.

[ubarch]

So, work continues... I just finished two major parts of the stand form.

Instead of opting for the steel beam design in the Forno Bravo plans, and instead of opting for a square entrance made by pouring an entirely planar stand ceiling, I decided to try form an archway with concrete. I have always loved (Brutalist architecture). I sandwiched the stand entryway between two planes of 3/4" plywood, and used pieces of 2x4 to make them clamp down on a curved cardboard concrete form. I used a piece of pegboard (which is more flexible and springy) to improve the arch symmetry and mold finish. I also used clay to round the edges. I packed it into the 90-degree angles formed by the mold and dragged a beer bottle across them to get a consistent radius. For strength, I bent a piece of rebar into an arch, which I plan to cast into the concrete. I'm trying to think of some cool designs I can produce in negative to make a neat archway.

This left me with an additional advantage: the inner lip of the plywood "Sandwich" could be used to support the bottom of the tray structure. I still build the framing and such as explained in the guide, but I moved one of the 2x4 supports slightly to more evenly bear the load. Shimming all this was a pain; my foundation is neither level nor smooth, and I ended up using 18 2x4 segments.

One thing that confused me about the instructions: When building the framing that supports the tray (section 3), they aren't clear on whether or not you should fasten the plywood sheets of the tray to the 2x4 supports. I can see reasons for and against doing this: If I do it, the tray will be more stable. If I don't the tray will be easier to remove once the mold sets.

What did you all do? Is there anything I can do to make the arch better, or is it a bad idea?

[ubarch]

One more question:

How did you all get all the concrete mixed and into the form before it started curing? At 60-80F this season, about how much time do I have before the concrete solidifies?

I have a concrete mixing attachment for my drill. I was thinking of trying to mix in 2.5 gallon batches in a 5 gallon bucket, and just lift them up and dump them into the form. This might work if I have an hour or so until the concrete starts getting hard... To level the top surface, I need to be able to drag a straight board across the top of the form.

Finished the form just now. Will post pictures later.

[ubarch]

More pictures and questions:

How do you all bend rebar? I can't get a sharp bend. I tried heating it with a torch and that wasn't so successful... Is there a special tool?

Here are pictures of my completed concrete form. You can see a couple attempts at bending rebar there in the foreground.

[alexi82]

Originally Posted by ubarch

Browsing this site can be downright discouraging; some of the dudes on here seem to be doing masonry work as if it were going to be a critical component of a space shuttle.

haha tell me about it...

i've learned now not to get discouraged. there is some great tips on here and everyone knows what they are on about. i've done my oven to the best of my abilities and the next one i do when i move in a few years i'll have learnt from my mistakes and from all the awesome advice on this forum in the end if your oven works its a good thing!

[fxpose]

Originally Posted by ubarch

How do you all bend rebar? I can't get a sharp bend.

For sharp bends you can insert the rebar in 2 lengths of steel pipes and make the bend.

[ubarch]

Poured the top of the stand yesterday.

Some observations:

-I found that rebar tie wire (as recommended in the instructions) was really hard to use. It was much, much easier to just tack weld the rebar pieces in place.

-fxpose's suggestions about using steel pipe lengths to bend rebar worked great. I bought 1/2" ID pipe for 1/2" rebar, though, and some of the pieces didn't fit without pounding the ends.

-I used ordinary Sakrete. I was a little nervous about this because at Home Depot there are other, more expensive mixes that say they have higher strength. However, I couldn't find any mention on here of proper sack-mix concrete brands, and the instructions didn't seem to mention anything either. Sakrete's "5000 plus" product is more expensive, but also lists that it meets the same spec as ordinary Sakrete.

-We mixed each bag individually in a 5gal bucket. I have a rather large drill with a paint mixing attachment that made this go pretty quickly. It sort of acts like flour. I also found that the following technique works pretty well for mixing this way:
-Add 4 quarts of water to bucket.
-Add about 3/4 to 4/5 of the concrete mix.
-Mix. The result should be very thin and soupy.
-Add the rest of the concrete, and mix.

-We finished up at about 9:00pm. I woke up at about 7:30 and covered the set concrete in water, and I'll do that throughout the day to help it cure.

Pictures attached.