Bob Drzymkowski

Uh oh, I guess I'll be the experiment with metal stitches!

I'll buy the lime tomorrow , then see what the bag says about mixing. Kiko Denzir says a basic lime plaster is made of 3-4 parts sand to 1 part lime, and just enough water to make it workable. Seems clay would be a good addition. Maybe wheat paste? How do I make "rice soup"?
I think you're suggestion of test batches makes sense so that's what I'll do this week.

Made 4 pizzas last night--this oven is awesome--I love it!

Bob

This one shows the hairline crack after a good firing...

Jay and others--My patch job seems to be successful. The stitch technique worked great. As you can see from the pics I used a hardware modification, reasoning that with wider ends (wing nut/washer) it would give more resistance to pulling apart. The last 2 show the cracks after a full-on firing--just minor hair-line cracks now that will be hidden/strengthened by the final lime plaster layer.

I'm now about ready for that final plaster. I checked with my local stone and masonry place and they have 1 kind of lime, the type they sell to masons, no other distinction. So what do you suggest for a mix? Also I'd like to make it as weather-resistent as possible; I think I'm more concerned with resistance to rain than having it be breathable, since almost all of my use will be with a hot oven, like pizzas.

Bob

:-]

Jay,The Kiko I refer to is the author of "Build your own earth oven" I have the 3rd edition, Kiko Denzer. I'm a novice at this and from my web searches this past winter this is the name and book most often used as a reference for cob ovens.

Thanks for the warning about web "experts", I know there are many out there in all fields. I will start checking for lime sources and get back to you.

Bob

Thanks Jay, I'll let you know how the patch turned out and also when I start looking for lime. For the finish plaster Kiko recommends 3-4 parts sand to 1 part lime--is that approx. what you use? No soil or clay? Fiber?

Jay--thanks for the kudos. Yes, I really like the oven, my first. I baked in to once--got it up to about 5-600 deg, roasted some veggies first, then 3 pizzas, followed by a loaf of bread when the temp had dropped to the 350-400 deg range, followed by a pans of muffins!

I used the term "mortar" but I meant the cob mixture. My soil is clay-poor so I add "fire clay" and sand. That's what I'll patch with + some straw cut up < 1.5". And I'm glad I asked about cool or hot--I will do it cool, probably today.

I'm waiting to fire it several times before the final lime-plaster layer. I live in eastern Washington where the summers are usually hot and dry (hotter and drier each year unfortunately!). I could build a roof of some sort over it if I have to but I'd rather have an outer layer that I don't have to worry about (rain and snow other times of year). and I don't think I have to be that concerned with breathability 'cuz I don't plan on baking too much bread, so I won't be using it as Kiko does (remove all embers, close door and bake with radiant heat and steam)--mostly pizza, with coals pushed to the back while balking. Do you have a recipe for my outer layer?

Bob

Thanks for your comments and for sharing your experience Jay. Smoke does not come from the crack, so the inside layer must be intact. For the stick keys are you saying space them 100mm apart so it ends up looking like the stitches scar on my ankle? And what should I use as the key, sticks? I have a mortar mix ready to add water and plan to add straw to the mix--seems this would add adequate fiber.

Since the crack expands when the oven is fully heated and then shrinks back to what you see in the picture-about a fat 1/4" at the max, I think I'll patch after heating the oven fully. That way the cob will shrink around the patch rather than continuing to expand from the patch when heated. What do you think?

John the Pollinator--Thanks for the comments. The crack doesn't appear to go all the way thru--no smoke out of fissure. I had planned on using straw for fiber in the inlsulating layer, but in the end went with the cedar shavings--now I don't remember why. I'll try to patch with a high fiber/Ewell Gibons-type mix. I forgot to mention that I plan on adding a finish plaster layer, and I will be sure to add straw.

Greetings--New to this post and I'm sure something close has been discussed but here's my story: As you can see I have a healthy crack, what you see is the worst of it--about 3/8" wide at the extreme. This was my first time baking, so I had a pretty hot fire. First 3" layer 2 weeks ago, 3" insulating layer the next day, 90 degree air temps throughout. First firing about 5 days later, small fire, no cracking. Then a little hotter firing a couple days later (7 days from building now), and crack begins. 2+ hour fire enough to get floor to about 400 deg and crack gets a little bigger ( using Kiko as guide, he talks about starting small fires almost immediatly so I thought I was OK, especially with the hot days here). My cob recipe, almost no clay in soil so I added "fire clay", about 1.5 parts to 3 parts soil; 1 part clay/soil mix to a little less than 2 parts sand (mason's sand). I used a healthy amount of cedar shavings in the insul layer--the kind you get for pet bedding.

So getting to the crux of my question, assuming my oven is salvageable, what's the best way to fill this crack? I think there are a few contributing factors to why it cracked: the cob is a little thin around my flue, the flue itself presents weakness in the cob not only 'cuz of the thin cob around the front of the flue but it also has "seams" or joints that will show shrinkage. Not sure I had the ideal clay/sand ratio, and I now see I was probably in too big of a hurry to get it dried out and ready for pizza.

I think it's done shrinking, other than whatever expansion/contraction I'll always get when firing. I think cob mortar is my best bet. but what bout a silicon based calk or other concrete or mortar crack filler?

Long winded but I think I answered most questions. Thanks in advance!

Bob