obligatory crack photo

[dougrappe]

Hi everyone, I think I've read every "crack thread" on the forum so I know this is to be expected, still shocking when it happens!

I have been curing with small fires over the course of a week. A small hairline crack appeared in the arch after the 3rd day, as I kept increasing the size of the fire the crack would gradually get larger and always close back up. Last night, it opened up quite a bit more, maybe 3/32 (2 mm) and I was surprised this morning to find that it had not closed back up. I can only guess at the dome temperature, but this was still a relatively small fire, the floor thermocouple got up to about 350F, after the fire was out. I have been taking it quite slow, my original plan was to cure slowly and add the insulation about half way through the curing process. So, I'm about the halfway point now, and considering what to do next. The crack goes through the arch on one side, up the dome and all of the way around and is working its way back through the other side of the vent arch.

Any thoughts are greatly appreciated as usual!

Doug

[dusty]

Re: obligatory crack photo

Doug,

I know the feeling...we all do. So sorry but that little thing looks very similar to what happened to mine. I was quite upset at first especially because it was in the front arch but I got over it. I used the oven for quite a while, probably over two months, until the crack seemed to stabilize, before I repaired it. You should take comfort in knowing that I have had no further problems and it looks great still.

dusty

[dougrappe]

Re: obligatory crack photo

Thanks Dusty, After another few fires, the crack has stayed open enough that I decided to fix it now rather than wait. I fully expect it to crack again, maybe this time it won't open up as much!

I was concerned with the opening and the crack migrating around the other side of the flue that the whole thing could shift, flue and all. Ground out the joint and cleaned it up and re-mortared. I'll start some curing fires again in another week. It's not like I don't have other stuff to keep me busy....enclosure, insulated door, tools, flue cap....

thanks again for the encouragement.

Doug

[Dino_Pizza]

Re: obligatory crack photo

Hi Doug, I looked over the pics of your build and it looks strong. Your bricks are tapered on the sides and tight but you used the mortar for tilting your bricks up (which is fine) but that's probably where the crack is circling around the dome. I've got 1 of those too but with your well-built dome, it will just use that area to expand a bit when hot and the weight of the dome will keep it closed. The oven will still absorb heat and release it for cooking just fine. Are you going to do vermic-conc spread on the dome or just the blankets? Either will help seal up the dome. Good job on mortaring the front arch crack. It seems like that's were it wants to be if it ain't closing up, so refilling it makes sense. I had my dome over 700* for hours last Saturday so my interior went completely white and everyone saw my crack . It's no big deal now. It's natural to worry but it will be just fine. Just a wait a few days for it to dry well start the fires again slowly. Good luck, Dino

[Lars]

Re: obligatory crack photo

Doug,
If you have read all about everyone else's cracks, then you undoubtedly saw my last post. I was a bit disappointed in the whole WFO idea. I let my curing fires burn for quite a while and am NOWHERE NEAR high baking temps.

I went ahead and put blankets on and did my vermiculite dome. The fires I made produced a crack that came all the way out to my house brick arch. I am pretty sure mine happened when the bottom of the bricks heated up and the tops did not.

Masonry products DO expand with heat! We are all learning that with every crack! I think the main reason is that the inside of the dome heats up and expands while the bulk of the mass is still cool. It is literally prying apart the dome and arches and the weakest point.

I guess we must just go ahead and understand that the 'heated' shape it needs to assume is with that particular crack, then just mortar in enough to cover up the visible (least desirable) crack, and let the structure be open for expansion when being used. That's what I plan to do, though I haven't gotten it fully up to high temps yet.

I am really excited to see the inside of the dome burn white, but with this heat wave, I haven't been too excited to burn fires, you know.

As far as the stucco and vermiculite dome, I am pretty sure there is enough 'give' in the blankets, that any dome cracks will not propagate to the outer stucco shell. I have my 'scratch' coat on now and planning on doing the 'brown' coat tomorrow morning.

Lars.

[dougrappe]

Re: obligatory crack photo

Hey Dino, thanks for the feedback, I was kind of mulling over what to do the other morning and before I really knew what I was doing I had the circular saw out and had ground out that ugly gap. Kind of an impulse. (like this whole crazy oven project!) I feel much better now. It's actually gone remarkably well considering all the things that could go wrong, right? By the way, really looking forward to seeing your slate roof go up.

Lars, I think we both posted on the same day with arch cracks. I have to say I didn't think yours looked too bad (crack-envy?) Not that that should make you feel any better about it. So some repairs are inevitable I guess, the nice thing about domes and arches; they are self supporting by their nature so I don't think anything catastrophic awaits either of us. I've gone ahead with my insulation as well. Wishing you "the fires of hell" soon.

Doug

[Lars]

Re: obligatory crack photo

Hey Doug,
Well, have a look at my crack now!!! ( no, seriously) I have posted a few pics on my 'crack thread'.

I had my 'fires of hell' and the damn think has propagated through all five brick arches and the blankets and vermiculite layer AND a ways into the scratch coat ( stucco) up the dome! AAAGGHHH!

Furthermore... CRACK!!! PING!!!! my clay flue snapped open on the back.

Call me irresponsible, but I am going to take a different tack with this. I think I am going to mortar my visible arch crack while burning a fire. Worst case, something ELSE cracks when it cools ( and I learn yet another thing NOT to do) AND, I am just going to mortar in the clay flue and let it expand and open up a crack on the back side ( where else?) when I get it hot with fire.

I need to build up my vermiculite layer anyway between the top of my dome and the chimney ( clay flue section) so I think there may be a small roofing material that would protect the occasional ( when there's fire) crack from allowing rain/freeze/thaw problems from occurring.... I kind of like to 'design as I go'...

L.

[dougrappe]

Re: obligatory crack photo

Well Lars, this is a fine mess you've gotten yourself into, I just posted to your thread, there are as many repair techniques out there as there are oven cracks. (and those are just the ones people are sharing with us) The flue crack is disappointing, I'm expecting that "ping" myself one of these days.

I'm taking a wait and see approach, that's where I wait to find out what else happens to Lars' oven and see what he does about it.

Actually, I am feeling better about my "time out" waiting for my repair to set and cure. Plenty of other stuff to work on, and I was concerned that once I could cook in the oven I would just blow off actually completing it.

Good luck,

Doug