Another curing question

[pmgnut]

Hi all, I've been reading tons of information on curing a masonry oven once completed. Seems to be an overwhelming amount of information out there which is making me more confused. So upon completing the build, what's the next step? I'm guessing waiting one week even before burning a few newspapers is most definitely required. So after that, starting the first "real" fire, is the idea to get each and every firebrick to a low temp {say for sake of argument 100 degrees farenheit}. OR is the idea to get the overall oven heat from the fire to 100 degrees, and for how long?

my other question is rain. Suppose your oven is fully cured of moisture, you've gone through the step by step process now your done curing. then it rains on your oven. Do you have to go through the curing steps all over again?

[pmgnut]

Hi all, Jim from CT here. My son and I started an outdoor pizza oven a couple months back. We have the walls up, the platform on top of the walls, and last weekend we poured 5 1/2" portland/vermiculite mix for underneath the firebrick oven floor. This weekend the plan was to begin laying the firebrick floor on top of the vermiculite & portland slab. I realize when we get to the firebrick arch we will definitely need to use refractory/high heat mortar, but do we really need to use high heat mortar to lay the firebrick floor in place? I'm shocked at how the price of refractory mortar is going up by the day. Currently $74.00 for a 50lb bag! Can we use regular mortar underneath the firebrick floor? I mean, if a bed joint cracks, the firebrick can't really go anywhere, as the entire floor will eventually be surrounded by a dome/arch and backwall.

[Pizzarotic]

Relax, it will work just fine. There are many ways to build pizza ovens and most work just fine. The barrel arch design works well and you will make great pizzas. Sure, you can build an excellent oven for a lot of money, a good oven for a lot less or a mediocre one for cheap. They all work, some just better than others.

[david s]

On its own the powdered clay is a bit too fine and it makes the bricks settle too much.Think what would happen if you did the reverse and tried to use heavy aggregate as a levelling medium. It comes down to particle size.

[pmgnut]

Well since my last post we have done 8 curing fires and even cooked a frozen pizza just for kicks to see how it would work. The frozen pizza was the cheapest money could buy and not a brand I'd normally purchase for my regular electric home oven. Doctored it up with some olive oil and oregano it i have to say it was beyond delicious with the wood fired flavor. Bottom crust cooked beautifully. As for cracking- yes we did get two linear cracks on the bed joints on the outer red brick layer. The cracks are hardly noticeable when the oven is cold but when it heats up, the same cracks open up every time. Also a few hairline cracks in the back firebrick wall {joints} but as I said they are hairline cracks and do not appear to be an issue. I'm going to wait a while to grind out and fill the cracks in, as i want to see if any additional ones develop first, this way i can do it all at once. Overall the oven heats very nicely inside and burns quite well. A couple things we noticed - oven takes a good 60 to 90 minutes to get really get hot for cooking. The other thing is the obvious- the drier the wood the hotter and better it will burn

[pmgnut]

Hi all, I plan on finishing my build around mid to late October. My question is, as we get into the later , colder months and the dead of winter, I'm guessing firing the cold brick oven will cause massive thermal shock and potential cracking. I'm assuming its a good idea to begin very slowly with a low heat fire for a while in the winter months, or should it not be used at all?

[Pizzarotic]

Yes, very good idea. You could start with a heat lamp or a propane burner on low for a few days.

[UtahBeehiver]

The dome should be insulated but before you start the cure, this helps moderated the temperature differential between the inside and outside of the dome to help minimize cracking. Also, the use of BBQ briquettes is a good place to start, no direct flame and gets the oven to about 200 f. Slow and low is how you cure an oven. People get too impatient at this stage and go too fast too hot and damage their ovens.

[SableSprings]

There will be always be a difference in temps at the top of the dome and the lower sides. Obviously the apex will be the hottest. Curing is primarily about driving out the moisture as you know, so as the bricks/mortar dry out they heat up more quickly. When I fire my oven, the clearing always progresses from the top down. Take your temp readings in the top third of the dome for the first several firings, you want to minimize the difference between the top section and the next section down. By taking temps high & low, you can better control the temp disparity.

Spreading your briquettes out closer to the sides help heat the oven more evenly as you coax the heat to flow up the side walls instead of letting it head straight up to the top. As your oven starts to dry out, the normal breathing & heat flow of the dome design will naturally move that heat more evenly.throughout the oven. As Russell pointed out, too many new ovens are heated too quickly because it's such an initially slow process to drive that moisture out. Since the amount of contained moisture varies so much between build materials, climate, and provision for moisture escape routes...curing timetables and temps are mainly a generic guide.

Ovens that pick up moisture over the winter or wet season will generally need a couple low, slow fires to bring them back to good, working order. That's why you want to provide some sort of protection from the elements... Especially the insulation areas as they tend to readily absorb water (thankfully, newer materials are helping reduce that problem... hopefully the cost of those newer types of insulation will come down in the future).

Hope this info helps...just go slow & don't stress. There will be cracks, but the structural design has proven to be solid over thousands of years! Relax!

[pmgnut]

Well we lit the first curing fire yesterday and overall it went well. I had completely forgotten about the briquette method so the very top of the oven of course got hotter than 150 degrees so to remedy that quickly I just spread the fire out a bit wider amongst the floor. I also fabricated a door out of heavy gauge 1/8 steel scrap on Saturday. The slot on the right was already there so i just left it as a peek hole. Next fire I will have a bag of briquettes for sure.

[pmgnut]

I see an ove glove purchase in the near future ;}

Sable springs- thank you for the info, very helpful!

[Sixto]

I see an ove glove purchase in the near future ;}

The door looks great, I purchased a pair of welding gloves from my local builders supply store for $6.00 and they are working out really well.

[pmgnut]

Thank you Sixto, I don't have a welder so I just drilled , bolted and screwed together, it's a pretty solid door

[pmgnut]

What is the correct method of curing? I have read where one should peg the max desired temp then burn for minimum 3 or 4 hours {longer the better} then in the sticky section i read it mentions "Let the oven fall back to cool as soon as you reach the temperature you want. " , its awfully confusing

I also just read the Forno Bravo instructions where it says do not use charcoal for curing

When curing your wood fired oven, only use solid wood fuels.

• DO NOT USE charcoal, pressure treated lumber, chipped wood products, sappy wood such as pine, laminated wood, or any material other than dry, medium- or hard-firewood.

[Pizzarotic]

Hi pmgnut, there is no hard and fast rules for curing an oven and there are also a lot of variables for each oven like construction type, type of mortar, thickness, oven size, insulation, climate etc.

The first step is to wet cure the Portland cement/mortars for 7 days followed by up to 14 days dry cure for your cement/mortar to reach design strength. (This is the ideal, most people struggle with 14 days total)

After that the goal is to drive out the significant amount of moisture held in the oven using a heat source without turning the moisture to steam.

In my experience the ideal way to do this is with a controlled heat source like an electric or propane heater to heat the oven to MAX 200°f and hold it at that temp for as long as nessasary to remove the bulk of the moisture, which could be several days or more.

Next comes the curing fires at progressively higher temps on a daily basis up to 7 days. Here, the idea is to heat the oven to the progressive temperature for an hour or two to allow the oven mass to saturate then seal the oven and let it sit whilst the heat progresses through the oven mass and insulation with the oven retaining more and more heat as the firings progress each day and fully drying the oven.

Each oven is different, everyone cures their oven differently, some not at all. Slow and long is appropriate, as is observation on how your oven is behaving. Worst that can happen is you get a minor crack.
Enjoy

[pmgnut]

Thanks for the reply. I ended up using charcoal briquetes last night, started with a pile and added more as they heated up. Eventually had one single layer spread evenly across the entire oven floor, front to back, it had a nice even steady heat, hoovering around 200 to 220. I let it burn out naturally.

[pmgnut]

Just for kicks, the first cooking "test" we used a super cheap no frills brand frozen pizza. Wow it was good with that wood fired flavor.

[pmgnut]

We used the oven all day yesterday, topped out at about 700 degrees give or take. Pizza was awesome, took about 5 minutes per pie . The same cracks are opening up every time we fire it. Does this mean there is still moisture somewhere or is this common even when fully cured?

[SableSprings]

The normal brick expansion during firing will represent itself in the cracks opening up...this is not a result of retained moisture at this point. The "old school" bakers would often use the crack's size as an indicator for the oven's heat saturation & temp. Domes are normally very stable structurally and the expansion/contraction is consistent...in the half barrel design, such as yours, the outward forces may cause shifting of the bricks. This shifting can result in the barrel's collapse as the bricks work their way outward. Most ovens that use this design are buttressed on the outside to keep the bricks from the tendency for outward movement. You might consider doing that for your oven if you notice the cracks getting bigger & not closing back up when the oven cools. I don't want to "strike fear" in your heart...your build looks great...just something you need to be aware of...