Share your crack stories

[david s]

Re: Share your crack stories

So is there anyone out there who can support the theory that the soldiers are structurally superior. If not is the sole reason to obtain extra height at the perimeter?

[stonecutter]

Re: Share your crack stories

So is there anyone out there who can support the theory that the soldiers are structurally superior.

No reasoning that has to do with physics or real masonry knowledge would support that. This is a good concise reason..

Its all about lateral thrust, the enemy of brickwork...
Soldiers are inherently weak.

Any tall relatively thin walled masonry structure which is load bearing, needs some sort of buttressing...if the load exceeds what the wall will carry without it. Most ovens do not exceed that capacity on their own, so in most cases you will be successful with only the brick soldier. And if the oven is encapsulated in some sort of vcrete or similar material, then that acts like buttressing.

If not is the sole reason to obtain extra height at the perimeter?

David, I would agree that this would be a good reason why soldiers are a popular technique.

What I would be interested in seeing is how big of a diameter you could go before buttressing becomes necessary. So far, the largest I have done is a 42" Neo...no buttressing. I would think larger ovens would need it, as the larger diameter means more courses, which means more weight, which translates into greater lateral thrust

[AaronTheGeek]

Re: Share your crack stories

So is there anyone out there who can support the theory that the soldiers are structurally superior. If not is the sole reason to obtain extra height at the perimeter?

I can't comment on the structural aspects of soldiers but more than one person has said that they used soldiers to avoid a horizontal mortar joint at floor level. I guess they were worried about ramming their peels into it. Someone else had the idea of starting out the dome with a row of splits to avoid this.

~Aaron

[brickie in oz]

Re: Share your crack stories

If not is the sole reason to obtain extra height at the perimeter?

It would be easier to gain extra height by just laying the first few courses level.

[david s]

Re: Share your crack stories

I have never really understood why a soldier course is recommended. Usually cracks in the dome begin at the base, which is the weak point of the dome and want to travel vertically. By doing a soldier course you are merely encouraging this to occur. The only advantage that I can see is that you get a little extra height at the perimeter of the dome. That could be achieved by laying two normal courses without leaning them in on the dome radius profile and laying them in bond. Is the soldier course recommended in the Pompeii plans and if so can anyone support it's advantages?

Yes, I agree.

[V-wiz]

Re: Share your crack stories

Interesting read. Question, when building the walls on the brick floor, do we mortar the bottom of the first coarse of the brick? so do we apply mortar to the bottom of the brick onto the brick floor?

[stonecutter]

Re: Share your crack stories

Interesting read. Question, when building the walls on the brick floor, do we mortar the bottom of the first coarse of the brick? so do we apply mortar to the bottom of the brick onto the brick floor?

No..well, at least I don't. It would break bond quickly and would be of no value if you did, because the walls and the floor brick will expand and contract at different rates during thermal cycles.

[Lburou]

Re: Share your crack stories

This is my crack thread, it includes pictures and repairs.

[V-wiz]

Re: Share your crack stories

No..well, at least I don't. It would break bond quickly and would be of no value if you did, because the walls and the floor brick will expand and contract at different rates during thermal cycles.

Thank you.

[CoyoteVB]

Re: Share your crack stories

So here is another one of my rookie theories on this crack. It might be be connected to the soldier course. During the curing process I followed the FB schedule. I even added a couple extra days of the top of the dome hitting 850-900F. The sides reached a temperature of around 500 and floor hit around 400 I think. Pizza time. I fire the oven in the middle until the clears. Next move the coals to the left side (side with the crack) and throw on some more wood. I am not sure how hot the sides got but I am sure it was a lot more than the 500F it reached during curing. I fired the oven several more times before the crack appeared. I am thinking there was a least a 400 degree jump between curing and first pizza. This may have been enough stress to create the crack.

[mikku]

Re: Share your crack stories

As a completely "unknowledgeable person" on the topic of brick. Here is my opinion why soldier course might be used.

Standing them on edge, with the thin face pointed inwards makes it very easy to make a rounded shape.

If splits are 1/2 thickness brick; then they would produce even a smoother arch.

Cast the normal soldier course area from refractory castable--then wait for it to break wherever it pleases, then blame it on shrinkage!

[stonecutter]

Re: Share your crack stories

I have never really understood why a soldier course is recommended.

I re-read your post and it occurred to me that I answered with a Neapolitan dome in mind, not a Pompeii. I'm with you now, and there really is no advantage to starting with a soldier course that I can see.

[david s]

Re: Share your crack stories

As a completely "unknowledgeable person" on the topic of brick. Here is my opinion why soldier course might be used.

Standing them on edge, with the thin face pointed inwards makes it very easy to make a rounded shape.

If splits are 1/2 thickness brick; then they would produce even a smoother arch.

Cast the normal soldier course area from refractory castable--then wait for it to break wherever it pleases, then blame it on shrinkage!

Good point. Better still design about 3 or four joins in it where you want, making sure you span a brick over the top of each join.

[mikku]

Re: Share your crack stories

How similar are the coefficients for expansion of stainless steel and castable refractory? I am thinking they are very similar!

When we did linings of kilns, some areas that were difficult to build or that required special attention for abrasion were either gunned or rammed in place. We used stainless forks (forget the proper name) that were welded to the kiln steel shell. Then the area was built up to proper thickless.

Other areas, like in the pre-heat and cooler areas had same type of forks but then pourable refractory was used.

Ceiling areas had stainless anchors welded to an overhead steel structure that would retain a modified brick that resembled a cone, but square shaped cone if you can imagine that. Then we would form from below up to these bricks and fill from above with another type of castable.

In none of these applications did the castable and stainless anchors interact causing damage to the build.

With those "facts" in mind, do you think that you could use an inner reinforcement net of "stainless steel" similar to concrete mesh to prevent these cracks from ever occurring. Or prevent the cracks from opening that would cause a problem?

[david s]

Re: Share your crack stories

How similar are the coefficients for expansion of stainless steel and refractory

I don't know the answer, but it is rather complicated because they vary at different temperatures. Normal steel has almost the same expansion as structural concrete, but then it is not subject to the extreme temperature we use and not at such a high rate of temp rise.The recommended reinforcement for this application is stainless steel needles. I think this is largely because larger sizes will attract more heat because stainless steel is more conductive than the refractory and therefore attracts more heat to itself causing more expansion and resulting stress. With the needles, they are surrounded by more refractory and their heat is more easily dissipated into it resulting in similar temperatures with similar expansion. By the way normal steel is about 3 times more conductive than stainless so is therefore presumably not suitable for that reason, also corrodes more easily especially in the presence of heat. Stainless is about 10 times more conductive than brick (presumably castable refractory too)