Another Cracked Dome

[thebadger]

Gang,

Hoping to start the dome once I finish the hearth in the next month.

I've heard a lot about cracks. It seems the best way to prevent is:
Keeping the bricks moist
Staggreing the bricks
Curing strategy

Is there anything else I should know/do to prevent cracking? Or is it like concrete guys say "not a matter of if, but a matter of when."

Thanks
Dick

[gjbingham]

My thoughts (guesses) for minimizing cracks would be two:

1. Staggaring the mortar joints as much as possible
2. Use Refmix mortar - from what I remember, its thermal expansion properties are most similar to firebrick - I might be wrong on this.

A likely third would be to do custom brick cuts similar to Les, Acoma, Ken and JCG have done recently. This will probably minimize the amount of damage that a crack will produce. (Myself - I wouldn't attempt it. I was a hack with the saw.)

[Acoma]

I Agree. The thermo properties of the Refmix are most similar to bricks for heat tolerances. Beveling and consistancing, as well as the interior face is imortant. I personally took lot of extra time bonding, moistening, cleaning each brick along the process.

[jcg31]

Originally Posted by Acoma

Jim and RC, would you both say that you are happy with the new curing method, or if to redo, you would go the the old way?

Unfortunately I have nothing to compare to. I went with the new approach because it made sense to me. I will say the advantage for me from the all day approach was that I learned a great deal about my oven in the process. If you choose to go this way I would start with smaller fires initially, it may add a couple days to the process but probably would be worth it.

That said, it would be good to have those familiar with the expansion dynamics of each process chime in. Heating the oven up and cooling it all the way down as suggested by the original process may serve to "exercise" the oven a bit more.

On the other hand the constant heat certainly makes sense for driving out the moisture. Perhaps a combination of the two methods, where you keep the fires going all day but then instead of putting the door on at night you allow the oven to return to the outdoor temp before the next step of fire.

At this point I have built one oven, It would be good fto hear from all those in the community who have built and cured multiple ovens.

The other question I have seen a number of times on the forum, but have not seen an answer is : Is there a brick oven in use that does not have at least one crack in the dome? At the point I discovered my crack I thought it was the exception, after reading many posts on the subject I am thinking that cracks in the dome are the rule.

Jim

[james]

It reminds me of the old joke. There are two things that are certain for a new concrete patio. It will crack, and no one will ever steal it.

I think it is just part of the process, where no matter how hard you try and how slowly and accurately you cure you oven, little cracks just happen. It doesn't impair how well your oven will cook or how long it will last, and they really don't tend to grow over time. They settle down and last forever.

I hope this helps.

James

[christo]

I agree with James.

I freaked out about the hairline cracks in my oven after curing.

I'm almost at the anniversary of the oven build and the cracks are no larger.

I just got a huge smile on my face. Thinking of all the fires and all the good pizza bakes over the past year. And no more worries about cracking....

It's all good!

Christo

[edschmidt]

One quick thought on the repair, I know after all the work you put into it anything that sullies your baby can seem devistating. But if you fill the crack in the next time the oven is heated it could very well find a new place to crack. I know this isnt totally applicable, but when I installed my hardwood floors (6" wide brazillian maple) and the first winter they dried and there were 1/16-1/8" gaps. This upset me so I got to work an made all of these shims from the leftover flooring and filled in all the gaps to make it perfect again.....Until summer when the floor began to buckle. I know Im talking humidity, and your talking temp, but expansion is expansion. I Ended up removing the shims, finding a caulk which matched the color and allowed expansion. I dont know of any product that remains flexible for masons, but I would be careful about any repair.
eddie

[gjbingham]

Sooner or later, you're going to have to fire that thing up Robert.

Walk away for a couple of weeks, at least. Then you'll know you've gone way outside the box for the recommendation for curing the mortar. If you get a crack or two at that point, you won't second guess youself. You'll be able to live with it a lot easier. Go play with your kids, kiss your wife, quit sweating the crack that might appear. The oven will still perform like a champion for you.

Undoubtably, a new oven curing regimine will show up just as you've completed yours. What are you going to do? Panic? You did what what was considered to be the best way to cure your oven when you were ready to do so. Smile bro. ! You've got a pizza oven in your back yard! Thanks for all your help with mine - cracked as it may be.

[Xabia Jim]

I would add to the list of items to help reduce cracking during building...

keep your mortar on the stiffer side
keep the finished work moist

(at first I use a garden sprayer and after it's set the next day I'll use a hose). Runoff to the lower rings is a benefit!

They do a lot of stucco work in Spain where it's sunny, hot and dry. I saw a wall in progress and there were cracks all over it. They came back and washed it with a sponge or rag. I think they essentially floated some additional cement into the cracks.

And I think ed's got a point that the crack may shift to somewhere else. I think you'll see that crack reopen if you fill it.

Keep us informed.....we all learn to love cracks

[Acoma]

Ya, I am sure a hose sprayer would work in nice 70+ temps. Not with 20-30 temps outside of a tent. My inside stayed in the 50's for the most part during brick work. I am not sweating that. Solid as a rock, both dome and arch. I hope the chimney does the same, and no regrets of my building process. Definately agree with the stiffer side of mortar, moist bricks (soaked), cool environment. After I finished my chimney Tuesday am, I let it rest with the warm upper 40's outside. That late afternoon, I dismantled the tent, being that I have 2-4 inches of insulation blanket everywhere but the chimney cap. I placed two triple wrapped dense painter tarps over the chimney, then shelled the site with a monster waterproof tarp. Site is nice and clean now. My excitement, anxiety will start in 4 days.