Making a stone chamber on my gas bbq

[AntoT]

hey everyone, I have a weber natural gas bbq, with all its burners on high, I can achieve a steady temp of 850f. I have been making pizza on my bbq for a while now by using a fibrement stone as my base on half the bbq, close lid, 4 mins, very nice pizza.

Now, I want to elevate that pizza. So I purchased some fire bricks. 2.25"x4"x9", and using 2 bricks on their sides to make a left wall, 2 to make a right wall and 2 to make a back wall, with 1.5" of space from the rear brick wall to the fibrement, and a roof of fire bricks standing 3" above the actual pizza, now bear with me cause I haven't actually fired it up yet, I'm waiting on the front 6 roof stones to be cut in a tapered fashion so I can close the lid of the bbq all the way in order to properly saturate the stones to the point where they'll radiate heat. I'm hoping to bring my cook time from 4 mins down to 2 mins. I have non contact thermometer coming tomorrow.

And my question is, once I get my stones to proper heat, can I continuously bake pizzas while having the bbq lid open? I imagine it would take the stones 30-45 mins to properly absorb all the heat to the point theyd radiate it out. But I'm hoping I can just keep the lid up since the only place most of the heat can escape to is inside the chamber of stone and out the front cavity. I can have pictures soon. But I'm excited and hoping the theory of idea works practically.

[SableSprings]

So basically you're building a small stack of firebrick inside the BBQ that will act as a masonry vault. Remember that in our wood-fired ovens and in your BBQ, the fire must be constantly applied to keep the heat up. You will heat up that extra mass and it will give off radiant heat both toward the pizza chamber and to the outside. Keeping the heat on your BBQ to keep those bricks hot, will make the outside of those bricks pretty hot also. It sounds like a fun experiment and any heat storage/radiant heat you get from the bricks will help improve your pizza turnover time. Alton Brown (food network) once used a heavy clay flower pot inverted on a pizza stone on a BBQ to make a little bread oven...worked great, so your idea sounds like fun. My only concern is making sure those bricks are secured, so when you're cooking pizzas you don't have a tumble of hot bricks onto your deck.

Looking forward to some pics and further experiments with the souped up BBQ/Brick oven combo.

[scott123]

1. 8 fire brick splits (2.25"x4.5"x9"), in a typical 15K BTU home oven, take more than 2 hours to come up to 550 degrees. It sounds like you're using at least 14 bricks, and you're going up to 850. If you're working with 60K BTU, then that will help, but, if you want to saturate the bricks with heat, for that many bricks and that temperature, I'm thinking 2 hours, minimum.

2. A 2 minute bake, in a wood fired oven, is usually a dome temp of 1000+ and a hearth above 800. It's also an active fire and/or glowing embers on the side that are well north of 1000+. The proximity of the dome to the pizza makes a difference, so you won't need a 1000 degree ceiling if it's only 3" away, but it still has to be very hot- most likely north of 850. And that's if your grill can actually hit 850. Grill thermometers are notoriously unreliable, and even if you have a massive number of BTUs, 850 feels a little overly optimistic to me. Once you get the IR thermometer you'll have a much better sense of where you can reach.

3. If you cover the grill areas outside the walls with foil, you will force all the heat through the chamber you've built and you may not need the lid closed at all- even during the pre-heat. This actually will help trim your pre-heat, because you'll be heating the inner surface of the chamber to max temps, rather than trying to collect the heat in the lid and saturate the entire brick structure. The top of the ceiling bricks will lose heat to the surrounding air, but the bricks may be thick enough to provide enough insulation so that the inside of the ceiling reaches peak grill temp. If you do find yourself losing too much heat, add a layer of insulation over the whole thing.

I hate to be a pessimist, but I think your chances of a balanced 2 minute bake are pretty slim. Grills, even high BTU grills, are just not engineered to do 2 minute pizza. Rather than trying to hit 2 minutes, I would see what you can do to elevate your 4 minute game. A fibrament stone is the best stone for a grill, because of it's low conductivity, but, with the height of the lid, you're still probably seeing an imbalanced bake at 4 minutes- dark bottoms and pale tops with undermelted cheese. What you're building now has the potential to amp your top heat a bit and provide better balance at 4 minutes.

Assuming you're using a fibrament grill stone with the aluminum deflector, one thing I'd suggest trying is to put some stainless steel washers between the stone and the deflector. This will help direct a bit more heat to the top of the dome.

[deejayoh]

I don't think the stones that are on top of your chamber will absorb anywhere near the same amount of heat as the ones right above your heat source. So if your bottom stones are at 850, your top stones will be less than that. Probably much less with a 3" air gap. That's the opposite heat profile of a WFO . And if you leave the grill open, you won't have any heat circulating around the back side of the top stones, so it seems like it will exacerbate the problem.

[AntoT]

So I did an initial preheat, no cooking though. Made my dough last night for tomorrow nights pizza dinner.

I was able to get the stones trimmed so that I can close the BBQ lid completely. After a 2 hour preheat, with 3 of my 4 burners on high here's what my temps looked like with infrared thermometer.
Fibrement floor 5/8" thick 710f
Walls and roof 2.25" fire brick 665f (inside the chamber)
Walls and roof (outside the chamber 450f

with the lid off, the temp dropped to 700f and 650f respectively.

So what kind of cooking time can I shoot for at these temps? 3 mins?

I tried posting a pic of the set up but the pic uploads upsidedown. Even if I rotate it in my phone it uploads upsidedown. Should I post it anyways?

Also, the roof bricks are supported my 1/8" stainless feel angle iron. 2 channels. No chance of them falling.

[AntoT]

Deejayoh, I do have a 2" gap in the floor from my fibremebt stone to the back wall, and the sidewalks are all the way left and right cover the entire grill surface, so all the heat can only scale through the chamber. You thoughts of heat and airflow were my first concerns I had to deal with.

[scott123]

Yes, 710 feels a bit more realistic for a grill.

Why did you use only 3 of the 4 burners? That extra burner should have bought you a few more degrees.

Did you add the stainless steel washers under the fibrament stone like I recommended? That should buy you better balance- hotter on the ceiling, cooler on the floor.

As I alluded to before, fire brick takes a long time to pre-heat. Fire bricks work beautifully in wood fired ovens, because the wood provides an abundance of BTUs, but in home ovens and grills, they tend to act like heat sponges and suck up a lot of heat. For NY style pizza, your numbers aren't horrible. If the washers end up flipping your numbers (700 roof, 650 floor), that should produce a half decent 3.5 to 4 minute bake. You might end up doming the pie a bit- getting the metal peel under the pie for a portion of the bake to slow the bottom down.

I'm guessing, since it's natural gas, you have it plumbed, so the gas usage from a 2 hour pre-heat, while potentially a bit costly, isn't going to involve numerous trips to fill tanks. Since you're most likely going to let your dough warm up about 2 hours, a 2 hour warm up probably isn't the end of the world, logistically speaking. If you want to bring those two hours down, though, start getting rid of the bricks. If, for instance, you swap the ceiling bricks with 1/8" steel plate, that should drop your pre-heat time considerably.

So what kind of cooking time can I shoot for at these temps? 3 mins?

While you're going to get different opinions on this, faster isn't always better. In other words, 3 minutes isn't better than 4. Instead of bake time, you want to look at this from a perspective of styles. Each style has been engineered to work the best with specific flours, cheeses, doughmaking methods and bake times. For instance, the 00 flour for Neapolitan pizza is stunning in a sub 90 second bake, but vastly inferior to malted flour when you get into longer 4ish minute NY bake times. The bake times between Neapolitan and NY, though, are kind of a pizza no man's land. Between 2 and 4 minutes, neither flour and neither cheese works all that well.

As I said before, while you were previously seeing 4 minute bakes, they weren't balanced. The cheese wasn't properly melted and the top of the rim wasn't sufficiently colored- either that or the bottom was way too dark. Your next huge jump in quality isn't going to happen by going from 4 to 3, but, rather, from an imbalanced 4 to a balanced 4 minute bake, using flour, cheese and dough making methods that are appropriate for that time. Sub 90 second Neapolitan pizza can be pretty spectacular, but 4 minute NY, properly executed, can be a life altering experience as well.

[AntoT]

Nice info Scott123. I have not put any washer under the floor stone. I was hesitant on the 4th burner thinking that the floor would get way hotter than the ceiling. I am using 00 flour and fresh mozzarella. Those thick bricks absorb an abundance of heat, but they also radiate that much more once saturated with the heat. I'm not concerned with gas consumption, it's direct lined into the house, and home heating is natural gas where I live. I costed my bbq on full blast to be somewhere around 25 cents an hour to run. Without the roof and wall stones, I was getting a fantastic bottom, nice puffy cornice, cheese melt was ok, but the colour was a tad on the pale side. I am hoping for more colour on top. Tomorrow can't come soon enough. 😊

Anyone have any ideas why my pics load upside down? Uploads from iPhone.

[AntoT]

Finally not an upside down pic.