Oven in Virginia

[ubarch]

Progress! Finally! ...Sort of!

I had some threads earlier in the Getting Started section about the foundation that I was working with (I didn't make it), which wasn't level. I was finally able to get time to mortar the stand together. I haven't poured concrete into the voids of the stand yet, but I thought I'd share some of the photos of the mortar'd structure.

We did this last weekend, when it was so hot that the mortar would set within 3 minutes. The bottom two courses of cinder blocks had to have mortar mixed for two blocks at a time. It rained later int he day and that gave us about 20 minutes of working time per mixed batch.

There were also mistakes, pictured below. The batch of cinder blocks I got from Home Depot were of differing sizes, so I had to shave material off of some of them to make the stand fit together. The last course was laid in an improper sequence, so there is both a gap and an overhang. The leftmost wall is also a little bit skewed. I think this is because the bottom course of cinder blocks had to have the least amount of material removed via diamond saw (under an inch) and it was hard to maintain accuracy when cutting that shallow. Should I let these mistakes slide, and just try to cover them up? To the left of the stand is a basic grill that I decided to throw together as long as I was stacking blocks. This should buttress the stand in case the leftmost wall is weak.

[DaveW]

Re: Oven in Virginia

Looks good to me. It sounds like you mixed your mortar a little dry based on a 3 minute set time but from what I understand dry is stronger. I mixed mine a little wet to extend working time in the heat, but it probably is weaker than yours. Part of the game is fixing mistakes. I consider that progress. Knocking it down would be moving backwards. Keep going!
Dave

[ubarch]

Re: Oven in Virginia

That's exactly what I was thinking at the beginning, so we were mixing up stuff with the consistency of beef stew. At the hottest point of the day, we could still only get two blocks per mixture. We had a bit of rain in the afternoon, and our set time immediately went to about 20 minutes.

[GianniFocaccia]

Re: Oven in Virginia

I wouldn't worry about the minor stuff. It looks like you could insert a piece off a block cutoff into that gap and mortar the edges clean if you want. I might trim the extending block with an angle grinder but you can always do that when you have a free ten minutes.

When you bend and extend your support slab rebar into the stand wall and fill with concrete, the entire structure will be solid.

John

[DaveW]

Re: Oven in Virginia

When you bend and extend your support slab rebar into the stand wall and fill with concrete, the entire structure will be solid.

John

That is a good idea, for some reason I didn't do that.

ubarch,
If you really want to beef it up you can create a bond beam as is required on the top of all residential concrete walls and in every other course of retaining walls. Just run your skill saw through the blocks, knock out the tabs, and run rebar longitudinally in addition to your vertical and j bars.

If you are going to take the time to build it, why not overbuild it?

Dave

[ubarch]

Re: Oven in Virginia

Finished mortaring this weekend. You can see the grill portion of the project clearly in the photo below.

Two questions:

GianniFocaccia said,

When you bend and extend your support slab rebar into the stand wall and fill with concrete, the entire structure will be solid.

My next steps were going to involve filling every other cinder block core with concrete, and while it's still wet, inserting the rebar pieces shown in the photo. I'd bend the rebar 90 degrees so that the excess extends into the hearth slab. Is this what you're talking about, or are you saying I should fill the cores and pour the slab all at the same time?

Also:

The grill is pretty simple, as you can see. The idea is to cut the excess from the rebar going into the grill, and use that as metal stock to frame a couple pieces of expanded steel. One will hold the coals, the other will hold food. I was going to line it with plain red brick for heat resistance, but do you think that's necessary?

[GianniFocaccia]

Re: Oven in Virginia

Yes, bending your rebar 90deg so that it extends both into your support slab and down into your block column is ideal. I filled the columns and poured the support slab in one pour.

If you can swing it, line your grill with firebrick. Common reds will not last very long and bare concrete even shorter.

All in all you're looking good and will be starting your oven before long.

[Brauma]

Re: Oven in Virginia

Looks like a great foundation. Where in VA are you?

[ubarch]

Re: Oven in Virginia

Thanks; all I see are the mistakes. 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.

I'm in Falls Church.

[GianniFocaccia]

Re: Oven in Virginia

I'm the same way - I tend to dwell on the imperfections long after I've moved onto the next phase. However, I am (I think) successful at using that scrutiny to ensure I don't make the same mistake again. If I didn't do this or quit altogether I'd be no better for it. This way I can practice the art of 'continuous improvement' and whatever I end up with can be proud of what I've built and call it mine.

[Neil2]

Re: Oven in Virginia

"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]

Re: Oven in Virginia

"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]

Re: Oven in Virginia

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]

Re: Oven in Virginia

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]

Re: Oven in Virginia

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.