Author Topic: I ordered a WFO (Read 28134 times)

norma427 · « **Reply #20 on:** July 23, 2012, 07:59:51 AM »

Gene,

I am anxious to see your WFO!

I am guessing Tom is helping.

Norma

Jet_deck · « **Reply #21 on:** July 23, 2012, 02:30:35 PM »

Yes, Tom is doing all the work. He is building it on a concrete base. When I get it, I will build a stand (steel) for it. Get this-- when I asked how long it would take, he said a couple of days. Then a week to dry and fire. Too cool.

Tscarborough · « **Reply #22 on:** July 23, 2012, 03:11:58 PM »

Should have all the parts delivered tomorrow.

scott123 · « **Reply #23 on:** July 23, 2012, 03:31:51 PM »

Quote from: Jet_deck on July 23, 2012, 02:30:35 PM

Get this-- when I asked how long it would take, he said a couple of days. Then a week to dry and fire.

How is this possible? You're putting perlcrete under the hearth, correct? Doesn't perlcrete take at least 7 days to cure properly? And what about letting it dry? Here they talk about a few weeks for letting the perlcrete sub-hearth cure and dry before proceeding with the rest of the oven:

http://www.fornobravo.com/forum/f14/pouring-hearth-14905.html#post113466

Even if you're insulating the hearth with board, you're still talking about the same few week wait for the perlcrete insulating the dome, and that's not even counting the drying time for the rest of the oven.

As far as drying goes, I've never come across anyone who felt like they dried their oven too slow, but there's countless number of people who rushed it and have regrets. If I was drying an oven that I spent this much time and money on, I'd let it air dry for a month minimum, then put a hair dryer in it, on a timer, for a couple days, and gradually move up to an actual fire over the course of another month. Overkill? Probably, but if I'm going to be using this oven for at least 15 years, what's 2 month's drying time to be 150% certain that I don't damage it at the start?

You cannot dry out an oven over too long a period, imo.

Tscarborough · « **Reply #24 on:** July 23, 2012, 03:45:18 PM »

2 days to build the dome. Perlcrete is ready the next day. So it goes like this:

Day 1 pour the slab
Day 2 pour the perlcrete
Day 3 lay the hearth and begin the dome
Day 4 finish dome begin drying.
Day 5 more drying apply perlcrete to dome
Day 6 more drying
Day 7 more drying

Tscarborough · « **Reply #25 on:** July 23, 2012, 03:46:03 PM »

You are not involved in construction, I take it Scott?

scott123 · « **Reply #26 on:** July 23, 2012, 04:27:37 PM »

Tom, do I really need to be 'in construction' to understand how cement cures and how improper drying can damage an oven?

http://www.fornobravo.com/forum/f16/oven-curing-767.html#post3871

Quote from: dmun

I think a lot of the discussion of curing the ovens overlooks an important point about the way concrete works. Concrete and ordinary mortars depend on their strength on creating a chemical-mechanical matrix between the aggregate (the stuff like gravel and sand) and the portland cement, which (to oversimplify) is a baked limestone powder. This process is called hydration, which to the casual reader might mean "get it wet", which is true enough, but what it really means is "keep it wet" for at least a week.

Isn't this common knowledge?

A week for curing. And, for drying:

http://www.fornobravo.com/forum/f16/oven-curing-767.html#post3869

Quote from: james

Curing your oven is an important step in the installation of any brick oven -- whether it is a Forno Bravo precast oven, a Forno Bravo Artigiano brick oven, or a Pompeii brick oven. Heating up your oven too fast can lead to cracks. You have invested a great deal of time, money and energy in your oven, so go slow, and cure your oven properly. If at all possible, don't schedule a pizza party the weekend your dome is finished.

After you have installed your oven, there is still a great deal of moisture in the mortars, hearth concrete, vermiculite, and the oven chamber and vent themselves. Each of these oven components was recently produced using an air-drying, water-based process. Simply letting the oven stand for a week does very little to "cure" the moisture out of them oven. In fact, the Forno Bravo precast oven producer recommends letting the oven stand for a week after it has been assmebled before "starting" the curing process. Thicker sections of concrete can take many weeks to cure.

You are trying to avoid two problems. First, any mortar or concrete that dries too fast shrinks and cracks. These cracks can let hot air and/or smoke escape from the oven chamber. Second, if you bring your oven up to heat while there is still sufficient moisture in the oven dome or mortars, you will actually create steam, which can produce hairline fractures, or even cracks in your oven. I heard a story (possibly an urban legend) from one of our installers who used to work with one of our competitor's ovens, where the home owner lit such a large fire in a non-cured oven that a chunck of the oven dome actually blew out the front door. Hmmm. Maybe.

Also, using a space heater can help, but only so far. It is not an alternative to fire curing. We ran a space heater in an assembled Forno Bravo precast oven for two days, then quickly heated the oven up, (don't do this at home -- it was an experiement to see what would happen to an oven that we have here) and we found that we created a very large amount of steam from the oven, mortars and vermiculite, which went on for hours and hours.

To be safe, here is a good curing schedule.

1. Let the oven sit for a week or so after you have finished the dome.
2. Run a series of seven fires, starting with a small, newspaper-only fire.
3. Increase the size of the fire each day by about 100F
200F
300F
400F
500F
600F
700F
800F
4. Let the oven fall back to cool as soon as you reach the temperature you want. It is important to bring the oven up to heat gently, then back down to cold, each time.
5. If you don't have an infrared thermometer, try this schedule:
Newspaper only
Newspaper and a little kindling
1 stick of 2"x3"X16" wood
2 sticks of wood
3 sticks of wood
4 sticks of wood
5 sticks of wood

James

I count 7 days on the drying side. But then, although James builds ovens for a living, he might not technically be 'in construction,' so perhaps his advice might not hold much water

David S might only be a visual arts teacher, but, with the number of ovens he's built, if he recommends a few weeks for allowing the perlcrete sub-hearth to dry in order to avoid future moisture issues, I'm going to believe him.

pizzaneer · « **Reply #27 on:** July 23, 2012, 04:44:37 PM »

I regret to say it, but I too would err on the side of caution with anything related to curing.

Why rush?

Tscarborough · « **Reply #28 on:** July 23, 2012, 04:48:19 PM »

The cure of concrete and mortar are 2 different things, and refractory mortar is another totally different thing. They all do share one characteristic: The rate of cure is not linear. For example, an adequately hydrated concrete will cure to 70% of final strength in 24 hours, 90% in one week, and 98 percent in a month. That is portland cement based concrete, but calcium silicate mortars perform at even faster cure rates.

The most obvious way to prevent excess moisture in the oven is not to introduce it. Dipping the bricks, using a wet mortar, cleaning the laid face with water, not covering the oven, etc are all things that are not required, BUT are very common for someone building an oven in their yard. That is why those instructions are all good and valuable, but as he says, "to be safe". He is in the business and has to be safe when instructing unknown people with various skill levels.

In construction (this is why I asked you), normal practice is to place concrete and strip the forms the next day, with CMU being laid the same day as an example of how normal construction is done as opposed to how it may be done by DIYers.

Tscarborough · « **Reply #29 on:** July 23, 2012, 04:57:50 PM »

Here is another example from FB, the lady is going to use muriatic to clean her masonry (not the oven itself), here is how I told her to do it, and it is the correct best safest way:

"You can use muriatic to remove mortar, just be aware that is a 15% solution of hydrochloric acid, nasty stuff!
To clean masonry with it, begin by hosing down the area to be cleaned and the entire area around what is to be cleaned. Not damp, but soaked. Do not use power washing equipment. Fill a bucket with water and pour the muriatic into the water (always pour the acid into the water, not vice-versa) at a ratio of between 10 to 15 parts water to one part acid. Wear PVC gloves, long sleeves, and eye protection. Apply the solution to the damp wall and scrub with a plastic brush if required. Rinse heavily to dilute the flushed solution. Do not use muriatic on soft, absorptive brick or dry masonry of any sort."

But that is not how I do it.

shuboyje · « **Reply #30 on:** July 23, 2012, 05:24:00 PM »

I've been around fornobravo a few years now, and know the regulars and their opinioned pretty well. If I had a techncal question about anything Portland based I would direct it to Tom. I consider curing time technical.

scott123 · « **Reply #31 on:** July 23, 2012, 06:46:45 PM »

Alright, Tom, I see what you're saying. 24 hour 70% strong perlcrete most likely has more than enough compressive strength in a WFO setting, but I'd still sleep better with the 98% I'm getting in a month. A WFO isn't relatively static like a house foundation, you've got a lot of thermal expansion and contraction going on. In that kind of rough environment, I want all the strength I can get.

On the drying side, though, are Jame's instructions really only for first timers/people with less skills? No matter how talented you are, a newly built WFO is going to contain a LOT of water- and if you drive that water off too quickly, you're going to get contraction and steam expansion.

How often do you see:

Noob: "Uh oh, I have a crack in my dome"
Experienced Builder: "It's no big deal."

You know what? I think it IS a big deal. I have a chipped tooth (from a piece of mortar buried in the sauce of a slice of pizza) that proves how big of a deal it is. Slower drying prevents cracks- to a point. If I cure/dry my oven 2 months and still end up with a crack, then I know that I did everything I could (and then some- way too much). 2 days of post perlcrete drying, though? I just can't see how you could possibly drive away that much moisture in that much time without damaging the oven.

scott123 · « **Reply #32 on:** July 23, 2012, 06:57:36 PM »

Quote from: shuboyje on July 23, 2012, 05:24:00 PM

I consider curing time technical.

Jeff, out of all the members of this forum, you've probably done more research on Neapolitan ovens than anyone. When Stefano Ferrara shows up and starts building an oven, are pizzerias baking pies within a week?

Tscarborough · « **Reply #33 on:** July 23, 2012, 07:13:45 PM »

There are 2 "cures" going on here. The first is the cure time of the mortar/concrete, the second is the cure time of the oven. On the first, there are no concerns about the concrete, the perlcrete, or the refractory mortar being set and hydrated to the point of design strength with a quick build. For curing the oven, longer is better, but there is no need to have an extended time for it, so long as it is done correctly. Most cracks in the oven are from thermal expansion and contraction and really have nothing to do with how long it takes to cure it. Most cracks, and all of the big ones I have seen are from building too big of a fire too fast, not too soon.

I will be keeping the oven clean and dry and begin building fires as soon as the perlcrete insulation is applied. Speed is of the essence for this step, since the stucco can not be applied until the perlcrete is dry.

shuboyje · « **Reply #34 on:** July 23, 2012, 11:00:40 PM »

The only place you will find info that detailed is in interviews with Stefano Ferrara. They are generally in italian and have to be read via web translation, so there is room for error. That said it seems pretty clear that Stefano feels the dome needs to be built in one day so it can all cure uniformly. I've read about the ovens being fired for two days straight the first time to gradually dry them out and bring them up to temperature, but I cannot say if there is any drying time prior to this. I'm gonna guess not. One major difference between a Neapolitan oven and an American built oven is the amount of moisture that needs to be driven off. Neapolitan ovens almost all use Tuff exclusively for insulation. Because of that there is much less moisture to drive off. An American oven tends to be at least partially insulated with perlcrete, which contains a huge amount of water. I would venture to say 99% of the moisture driven off durning early curing fires is from the insulation. As you can see the situations are totally different.

I've thought about this in the past, and dabbled with the idea of making precast blocks of perlcrete that can be hatcheted to shape just like Tuff. If the oven had a simple enough shape you could even precast sections to fit with no forming needed.

Tscarborough · « **Reply #35 on:** July 23, 2012, 11:22:52 PM »

Perlcrete does not require a lot of water, it is just easier to work when wet. The perlite component requires no water (other than that required to prevent excess drying from the wet mix), the portland is what has to be hydrated. Tuff is a pozzolan, similar in absorption to perlite, but it also has hydraulic properties of it's own.

Jet_deck · « **Reply #36 on:** July 24, 2012, 05:52:15 AM »

And this my friends is exactly why I park my boots here at night. My NY buddy looking out for me, and a Texas brick and mortar guy answering serious questions.

Jet_deck · « **Reply #37 on:** July 24, 2012, 01:12:21 PM »

And so it begins.

Jet_deck · « **Reply #38 on:** July 24, 2012, 01:13:58 PM »

Chicago Bob · « **Reply #39 on:** July 24, 2012, 01:18:50 PM »

All the best Gene....this should be awesome!