First time builder, wonder if I muffed it up?

[Age quod agis]

I have wanted a pizza oven forever. After a move a couple years ago to some acreage outside town I finally had space to give it a go. I have a bad M.O. of bull heading my way into projects with little research or experience, and this was no exception. By the time I had built what I thought would be an adequate base I began perusing the net to get an idea of how the heck I should proceed with an actual oven. This is when I found my base was WAY to small. I settled on a blog that I found of a guy in Britain that built a small half barrel vault type oven, and modified it's size to the largest dimensions that I could modify my base to fit. After much labor and expense, monetarily, time wise, and spousal frustration, I got the actual oven portion complete to the point of using it. The first attempt at pizza was after about 5 days of progressive firing. I registered 550 degrees on an oven thermometer at the entry of the oven, and the top the inside arch had just started to go white, i.e. burn off the black, when all of a sudden there were cracks all over my structure. So a question to experienced members: what kind of external cracking is to be expected? Now of course I have looked extensively into this since it happened. I have used the oven a few times since. I don't heat it as high, but the inside dome never gets white at all, just stays black. It gets hot enough to cook a pizza in 4 to 5 minutes, and my most available wood is cedar or S.P.F. 2X4 cut-offs, I also have access to pine and juniper. We are going into winter though now and the cracks that have spider webbed all over the structure expand when heated. I am afraid that being exposed to the elements will allow water intrusion. I wonder if I should worry that enough moisture can get in through these cracks that I will have to constantly worry about re-curing, and or is it possible to get enough into the perlicrete to freeze/thaw and bust things up. Seems that the cracks follow mortar lines primarily, there are a couple in actual firebricks inside, but mostly just all over the exterior. I understand thermal expansion is going to cause expansion, but I did not expect this level. Does anyone out there in wet, humid, and freezing areas have cracks in their structure? Do you worry about em? i.e. special treatment during firing after a storm or cold spell? When do the cracks stop if ever? I have probably only fired this up to cooking temp half a dozen times but every time it develops a new area of cracking. If or when they stabilize should I treat them with anything, or am I just overreacting? Anyway I have said enough for a first post. I am interested in info from seasoned professionals. I have monitored many posts here in my build, and am way overdue on registering, kinda wonder how my build would have been changed if I would have asked questions during. Anyway thanks for the read, I look forward to hearing from the pros.

[UtahBeehiver]

AQA,

It is a little difficult to determine the source of the cracking without some type of visual on the construction of your build. So take some pics and attach. Base on you narrative, you build a barrel style oven, so is it a pure 1/2 circle shape or does it have soldiers then a arched ceiling. Again pics will help.

As far as the oven not getting to the temps you want. Several factors could come into play. Floor insulation, without it, the base could act as a heat sink or the oven is still has some water in it. I take it you have not insulated the outside of the barrel yet but that would more likely affect the heat retention.

What type of material was used for the joints, how wide are the joints, etc. So send some pics and I am sure the gang can help you if possible.

Russell

[Gulf]

Age Quod Agis, Welcome to the forum.

You do need to keep the water out of the perlcrete and out of the oven. The oven's render cracks will only stabilize when you finally get the oven dry and keep it so. You are right to be worried about freeze/thaw (but, even in warm weather) the water soaked insulation and brick can receive/cause just as much damage, if the oven is fired to aggressively. Based on what info that I have, I think that is what is happening. The softwoods burn faster than hardwood, so keep in mind that they put a lot more flame impingement on the dome in a shorter period of time. If you have an idea that your oven is wet, you should always start over with the lower temp firings and then work your way up to pizza temps over several days. I think that if you can get your oven dry, keep it dry, and then apply a water resistant render, you will be fine. An open span covered roof over the oven will also help a bunch. Do you have some pics that you can post? Pics always help a lot .

[Age quod agis]

Well that was what I didn't want to hear, but kinda figured. I have to think of a way to cover this thing in a visually pleasing way. It is not in a place that really makes a free standing structure over it possible, I could do some sort of cover custom made to fit over it out of say R.V. cover material, I could even do this as something for the cold rainy/snowy months that would have a flap over the front and chimney so I could use it with the cover on. As for construction this thing morphed as I built. To answer specifics it does have 3 inches of 5 to 1 perlicrete under the hearth. It has average of 6 inches 5 to 1 perlicrete over the entire dome and back with field fence lengths in it for reinforcement. Unfortunately I didn't read about heat breaks till after it was built, so the closeout an the front which doubles as the back of the chimney, as well as the front entry and front hearth all act to draw some heat out of the chamber in uninsulated areas. I used firebricks in all areas subject to flame as well as the first 3 courses of chimney. I used HeatStop 50 non water soluble heat refractory for all the firebricks. The joints were usually around 3/8 inch give or take. Of course the dome bricks met at a V and had as much as 1 inch or so of heat refractory at the tops. It is what I call a half barrel vault, but it is laid with bricks vertically prior to running the dome. There are three courses of firebricks laid in a running course prior to the dome. I decided on a running course rather than soldier bricks as it just seamed stronger. Outside shell though is where I am seeing the major damage. Cracks seam to follow mortar joints, and are especially prevalent around the chimney and decorative wine bottle arches. I can go on and on about the build, it has been an intense 4 months of work between it and my pavered patio, and it still has to have the stone veneer put on the bottom pedestal. My main concern is what to do about the cracking, and how to mitigate the water issues. I would like to use it a couple times a week. But, if I leave it for a day or two in potentially snowy weather it takes half a week to prep it for a full temp firing. I am learning about soft vs. hard woods. I'm actually am prepping to take a trip over the mountains to get myself a cord or so of White Oak specifically for this thing. I could put some masonry sealant over the entire thing, but that won't fix the fact that the cracks look to run clear through to the perlicrete. I will have to try and get some pictures of the cracks in the daylight when this thing is fired up to show the extent of em. I realize that thermal expansion happens, and I recon I figured that I would experience some cracks, but there are some cracks for example that run the entire length of the spine from the chimney to the back of the exterior dome on this thing. Anyway I will post more later on details and history, for now anyone who was paying attention is no doubt sick of reading. Take a look at the pics and tell me if I am up the creek.
Cheers.

[Tscarborough]

I recommend paragraph breaks.

[david s]

I agree that we need more info and or pics of the build to make a considered diagnosis, but one thought comes to mind that perhaps you only have vermicrete as your insulation layer i.e. no blanket and that you rendered over this layer with a hard cement shell before driving out the considerable amount of water in the vermicrete. This leads to the vermicrete layer swelling and causing cracks in the outer shell.I learnt this one from bitter experience and now always use a layer of blanket which acts as an expansion joint between the inner oven and vermicrete layer. I also drive all the water out of the vermicrete layer before rendering over it with a hard shell.