A Very Big Mistake

A couple weekends ago, after I loaded my eighth and final load of bread, I noticed smoke coming out of the back of the oven. I quickly got the cordless drill and took the back panel off. I couldn't see anything, and therefore did not take much action for the next 10 minutes. Why was it smoking? I then proceeded to take the fiberglass insulation out of the oven (I hesitated because I knew I wouldn't be able to get it back in without taking the roof off, and I definitely did not want to do that) and was introduced to the flame which was burning up by the chimney. The fire extinguisher was emptied on it. Thankfully the damage was not too great, but a big lesson was learned.

When I built the oven, I seemed to overlook the issue of ventilating the oven, and separating the ventilation from the insulation. By ventilating the oven well, it would have prevented any wood (even the wood close to the chimney) from getting hot enough to combust. This would have been solved by putting in a ridge vent (which we ended up installing after the fire). But even if we did put in the ridge vent from the start, our fatal flaw was worse than not ventilating the oven.

The main thing we did wrong was to put a wooded 2x4 to tie together two rafters which ran right through the insulation close to the chimney and concrete cladding. This 2x4 had constant high heat surrounding it, trapped with the insulation. The wood dried up over the 10 months and eventually smoldered and combusted.

How we solved it: We moved all the wood at least 2 inches away from the chimney. We replaced that 2x4 which caught on fire with a metal tie. We installed a ridge vent and increased air flow from the eaves of the roof. We replaced all the fiberglass insulation with vermiculite so that no insulation would be touching any wood. There will now be enough airflow to prevent the wood from getting much warmer than the ambient air temperature, and the insulation is greater so that the oven actually stays hot longer.

We removed all the fiberglass and pushed aside the vermiculite so we could get in the oven to repair it. I was absolutely delighted, and quite honestly stunned, to see that there are no expansion cracks in the concrete cladding at all! Seems to me that refractory cement would certainly be overkill for any personal purposes, especially since we are firing it very hot for near commercial purposes twice a week and it is still in excellent condition.

10 Month Update

Hello Again!

It has been about 10 months since we have fired up our brick oven for the first time. To summarize, the performance of this little guy has GREATLY exceeded our expectations!

When we built the oven, we were expecting to be able to bake 6 loaves of bread with maybe 3-4 oven loads for a total of 18-24 loaves per firing. We would use this as the very first baby step for our 'business to be' and just bake bread for a dozen people one time a week. At first, this is all we baked, and our limit for one firing was about 25 loaves. Then the limit became 30... 35... then I started to fit 8 loaves per load... 9 loaves per load... 5 times... then 6 times. Our limit soon became 55 loaves per firing. Our customer base grew from just about a dozen people to almost 200 to date. We are baking bread on Fridays and Saturdays now. On Saturdays when the oven is really hot, we are able to bake 75 loaves (9 oven loads) with ease on one firing and I believe the potential to be close to 100 loaves (12 oven loads) with a really hot firing. Far from the 18 loaves we thought this oven would be capable of.

All in all, we are thrilled with the results of this oven. If I were to do it all over again, the only difference would be to not use a quartz countertop piece as the hearth stone the entrance of the oven. The extremely high heat melts the glue (or whatever holds it all together). I would recommend granite or brick. I have not opened the back to check and see what the cladding looks like, but from a performance standpoint, there are no problems. I will try to update this post when I take a peek.

With all that said, it is time to upgrade to a bigger oven!

Bread and Pizza

So it has been about a month and a half since we completed the oven, and it has been working fantastically for us. It has taken some getting used to as it is much different than the 5x7' oven we worked with previously, but products of the same standard are coming out of this smaller version.

Here is a general timeline for using this oven:

Saturday

10:00 - Start the fire, stoking it as needed

2:00 - In the case of a pizza party, this about when it would be. I would have focused the firing in the front 2/3 of the baking chamber because that is where the pizzas will be cooking. About 10-20 minutes before the first pizzas are ready to go in, push the fire to the back of the oven and clean the front half with rags and a broom. The pizzas should only take 3-5 minutes (with a naturally-leavened sourdough crust) depending on how hot the oven is.

4:00 - If you started firing at 10:00 for bread, and did not have a pizza party, this is when you would let the fire die out and let the coals linger.

5:00-5:30 - Scrape the remaining coals out of the oven, and put the door on the oven. This allows the heat to equalize before baking.

6:00-8:00 - Bake bread! Too many variables to try and explain here. For our naturally-leavened breads we bake them when the laser thermometer reads in the upper 500s (Fahrenheit).

Sunday - Don't forget to keep using the heat as the days pass! If the oven is insulated well, you can be using this oven for days. We would make beans, roasts, chicken legs, casseroles, baked french toast, potatoes, almost anything! If it is not quite high enough temperature, make a small fire with 3-5 pieces of wood (about 30-40 minute burn) and the oven will be pretty hot again for whatever you want to cook.

Monday-Wednesday - Still hot enough to reheat leftovers. Down with microwaves!

Thursday -Friday - Depending on whether or not you made more fires during the week, these days have had the perfect temperature for making yogurt (110F)! You can make a gallon of yogurt for the price of a gallon of milk, and you have the perfect way of making it.

Saturday - Make another fire and do it all over again!

Some pictures:

Days 12+ The Rest

The rest of the oven building has been a slow drawn out process of finishing the facade. This is something which will most likely be unique to every oven built. So with the materials which was available to me this is what I came up with:

The front arch was constructed the same way the inner arches were. These were made out of half brick in order to tie nicely into the front facade.

You can see the gap for putting insulation.

This was my contraption for bringing the brick up to the top. I did some math to follow ratio, then followed the line so that each brick's corner touches the line as it goes up.

Framed the roof in and am now ready to lay the rest of the chimney.

We made sure to tie the flashing in as we went up.

Decided to frame in the back part of the roof instead of laying brick just in case we needed to get in there. And it is a good thing because after the first day of firing, we needed to open it up.

Poured vermiculite in the sides and over the dome. I also utilized some fiberglass insulation.

The chimney cap is a piece of granite we salvaged out of the dumpster at a counter top manufacturer.

We probably needed at least 3 more bags of vermiculite to sufficiently insulate, so instead of paying the big bucks for that, we topped it off with fiberglass insulation. After doing some research, fiberglass is actually a better insulator than vermiculite. However some say it is not tolerant of extremely high heat like you would get in this oven because the resin holding it together might melt, but other sources said this was not true and that the melting temperature isn't until it gets into the 2000 degree range (nothing to worry about here). Since there was a layer of vermiculite first, I felt alright about it.

Here is a lesson learned however: I was told that you cannot over-insulate something and that there is no such thing as too much insulation. I think I found the loophole to that statement. If you look at the picture above and below, I stuffed it full full of insulation. But after the first day of firing, I took the top layer off because it was suffocating the oven and it was unable to breathe.

The most peculiar thing started happening after a hot fire. The oven started steaming out of the back, coming out at a steady pace like a really great humidifier. And it did not just do this for an hour or two. It came out constantly for 2 days. This was probably gallons of water escaping from the oven, and consequently, the fiberglass insulation took on this water as well. I am guessing a little rain got in and soaked into the masonry, and the oven, being as hot as it is, is not pushing all this moisture out. By putting insulation all the way to the top of the roof, I made it very hard for the vapor to escape. So we took the insulation along the ridge away and put a vent on the back (sorry, no pictures of this now, but I may update later with some. You just get to see the pictures of what not to do for now).

So... make sure you allow your oven to breathe. Also, I would fire your oven a while before you put insulation on so the moisture in the cladding or anything else can easily escape.

** UPDATE 3/2012: PLEASE READ LATER POST TITLED: "A VERY BIG MISTAKE". DO NOT FOLLOW THE GUIDELINES IN THIS POST FOR INSULATION AND ROOF CONSTRUCTION. VENTILATION IS VERY IMPORTANT, AND WAS LACKING IN THIS ORIGINAL DESIGN!**

Tar paper.

Shingles are on and flashing is being tied in.

The first flames!

The finished product!

Day 11 - The Cladding

If you are building an oven, you will notice as you go along that there will be times when you have to say to yourself "I wish I did it differently." I had a few of these moments today, but in the end, everything seems just right. The first thing is that I wish I made my hearth slab wider in order to give me thicker side walls. My side cladding is only 2.25 inches at the widest part, and only about an inch on the sides of the firebrick. It would have been great if my side cladding was 3 inches. As I put the reinforcing wire, the plans call for two layers, and with such thin walls, this seemed unreasonable. So the sides of my oven unfortunately just have one layer of reinforcing wire. The second thing I would have changed was that when I did the corners (right after putting in the arches), I would have used pieces of brick cut more precisely to make a smooth arch-like feel. These corners really give you a hard time when dealing with reinforcing wire and aluminum foil. And the third and more simple thing I would have done differently was to lay one more course of chimney brick so that my cladding could come higher in the front (but we found a solution to that, which you will see below).

So the first thing we did was wrap the oven in heavy duty aluminum foil. I originally thought that the purpose of this was to reflect heat back into the oven, but I was mistaken. The main purpose is to create some "slippage" so that when the bricks expand, it is not "glued" to the cladding. This way, both layers can expand and contract somewhat independently. After wrapping it with foil, I shaped the 6x6 reinforcing wire to end up in the middle of the poured cladding. My plan is 2.25 inches on the sides (wish it was 3), and 5 inches on the top. I put two layers of wire on the top (with bigger walls, I would have definitely put 2 layers on the sides as well). This process was painstakingly slow as I was trying to get the shape just perfect and ended up taking me a couple hours.

I kept a light in the oven prior to pouring in order to add some heat to the oven. This puts the bricks as somewhat of an expanded state at the time of the pour. This may help in preventing more serious cracking of the cladding (which is bound to happen after your first serious firing, but that is what the reinforcing wire is for).

All ready for the pour.

This was our solution to not adding another course to the chimney - just put in temporary bricks for the pour, and take them out once it has set some.

Put plastic and then a canopy over it to slow the curing process.

This was a little disaster that ended up being no big deal. Our corner busted open when the brick wedge at the bottom slipped out. We didn't want the concrete filling in the air gap between the hearth slab and the block wall, so I slipped some boards in there to prevent it from doing so. All this really did however was give me a thicker wall at the corner - just what I wanted right?

When the corner busted out, we tapped the walls to get the concrete settled a little too gingerly - leaving these air gaps. No big deal though, we just filled them with a sand/cement mixture.

Now we let it cure for a couple of weeks. Then pizza time!

Day 10 - Figuring Out That Darn Chimney

I have been thinking about this darn chimney since day one and have been dreading its arrival because I honestly did not know how it was going to work. Almost anyplace I looked I found inadequate instructions and missing pictures. I was pretty much lost when I started today, but it came together in its own sort of "just do it" kind of way.

One thing I struggled with was the integration of a clay flue pipe. I originally thought I would get an 8x8 flue pipe, and bring the side bricks (the ones on top of the granite slab) in 1-inch each course until it is the 8 inches apart I want. In order to do this however, the chimney will have just as much height in bricks stepping in as it will flue pipe. So this got me to thinking, do I really need a flue pipe? With a little research, I decided that I did not need a flue pipe. The whole purpose of it would be to prevent mortar corrosion which will eventually lead to a weakened chimney. To keep the story somewhat short, I am not worried about this. I will just make sure to clean the chimney every once in a while and it will be fine. Thinking about it, if the mortar which the flue is protecting is subject to corrosion, so is the mortar between all the bricks below the flue (the ones stepping in an inch with every course). So if the upper mortar joints (now unprotected in my new plan) would corrode, so would the bottom mortar joints (unprotected regardless of what plan you use). Therefore, if I ever for some reason need to replace the chimney (which I don't think I will have to) it would be because the bottom and top bricks alike have corroded... so why even protect some of them if it is not possible to protect all of them. Also, gases from wood are not as corrosive as gases from coal. In conclusion, I am no expert and may be missing something important, but this is where my logic has taken me. No clay flue liner for me!

Phew... now the chimney is a lot easier, but I am now approached by my next problem I have been wrestling with from day one. How do I start the back wall of the chimney on those slanted dome bricks which are coming towards the door? Even if I cut the bricks so that the first course of the chimney can be vertically level, the pressure will be pushed down and in. Ideally, you only want the pressure to go down. Once downward pressure is coupled with inward or outward pressure, it can be asking for trouble. But once again, I am probably being paranoid, especially since this is what it shows in The Bread Builders (inadequately in my opinion). So I am left to my own innovation. So I will just let you see the pictures and end this rambling.

Each course comes in one-inch

In between the third and fourth courses, I decided to put in this metal rod. The purpose is to hold in the back wall of the chimney from wanting to push in towards the doorway if the mortar does in fact ever weaken.

Before proceeding up further, it is wise to brace the bricks, especially if you have to whack the next course of brick to get it level. I actually got to the fourth course and had to start over because the first course lost its bond... I was evidently too rough on it and did not let each course properly set before moving on.

All four courses in place.

I cut pieces to fit the slant, leaving room for a mortar joint at the bottom of each one, and bringing it to the same level as the fourth course. These upright bricks will lean on the metal rod.

You can see here the shape of the bricks that fit on that slant.

This is what I set out to accomplish today. This wall is the front part of the frame in which we will pour the concrete cladding to (hopefully tomorrow).

This is the base of the chimney - it is just straight up from here.

Day 9 - The Dome

My original idea for starting the arch was to lay guide bricks on the wall at just the right angle to start the first arch bricks like in this picture below: 

However, getting these bricks cut in this way seemed more trouble than I was willing to bother going through when I knew I could fairly easily do it another way using hand-cut bricks. When we build our big oven someday however, this will undoubtedly be how we approach it. You will see what we decided to do below:

Before anything gets cemented in, make sure your arches are in just the right place by using wooden wedges.  Also, in order to fit an even number of bricks in the arch (to avoid special cutting a keystone piece), I had to actually lower the arch form just a tad and raise the first bricks out a bit so that they did not actually touch the wall bricks. This is OK though because all of its pressure is being thrusted into those wedge pieces. 

Special-cut wedge pieces were placed under the first bricks. You can see in this picture that the first brick actually is not touching the wall. This will be filled in with mortar as well. 

Fill in that bottom joint before you take the other bricks off the arch. This way you know that these first (and most critical) bricks are in the exact right height and angle. 

Then you start working your way to the center from both sides. 

I found it best to place the brick in with mortar on the back side only. Hold it in place with a wedge, and then stuff mortar into the joint. The most critical thing is to get the right angle so that the bottom edge has no gap and is a smooth transition from the previous brick. 

First arch done!

Second arch up and ready to mortar in. 

The last arch is in, and I am taking out the arch form for the last time. Exciting moment! 

It held just as expected!

Next row to go in is the front row. The bottom ends are resting in the angle iron and the tops are temporarily resting on a some lumber. 

I cut a special piece for each joint. 

Ready to be mortared in. 

This was by far the easiest mortar job yet. All you have to do is slap some mortar in between each brick and stick them together.

After you mortar in the special cuts, you can take the lumber out. Now its time to cut pieces for those pesky corners. You can see I mortared in some thin pieces of brick on top of the wall there to bring it to the same level as the longer firebrick door jam.  

Looks pretty good! You can see that the corner pieces are just to the best fit. I was able to just special cut the bottom piece and then just use half bricks for the top two layers.  

Now that's looking like something I can bake in!

It is best to let this fully cure before pouring the cement. What a convenient time to be going on a vacation so I don't have to be tempted to pour right away!