Should I fill a crack?

[Killeraye]

Hi all. I’ve built my 36” Pompeii with all the help of this forum. Thank you very much for your input. I’ve had questions the whole way through but mostly found the answers here. I’ll post pics of my experience eventually but right now I’d like to know if I should repair a crack I got during my very first small curing fire. I’m at the point of the final p-crete layer and waiting to give it a stucco/tile mosaic finish. I’ve ramped up the fires and cleared the dome but the crack looks pretty wide, coming back together when cool. It runs down the dome and out across my arch to the front. If I fill it when it’s warm and wide is the oven likely to crack somewhere else when it contracts back down?

[Killeraye]

Oops. Did I post this in the wrong location?

[david s]

Is the crack in the inner dome (brick or cast) or outer rendered shell (cement, thickness)?
A pic of your crack.would help.

[Killeraye]

[Killeraye]

Is the crack in the inner dome (brick or cast) or outer rendered shell (cement, thickness)?
A pic of your crack.would help.

Thanks David, (I’m Dave!)
I can’t see any cracks on the inside.
It’s a brick dome with 2” of p-crete then 3” of rockwool then 2 more inches of p-crete. I guess it’s just this shell that’s cracked but I’m surprised that it pulled my outer arch apart despite a 1/2” heat gap (filled with insulating fire brick and thinly mortared over exposed sides)

[david s]

That’s 4” vermicrete in total and as 1/3 of its volume is water, a huge amount to eliminate. I’d say your problem is probably pushing that water out too fast and it also looks like you have a cement rendered shell over the lot. It is advisable to push all the excess water out before doing a rendered outer shell because it makes water elimination easier, as does a vent in the outer shell, like a hole in a saucepan lid.

[Killeraye]

Ok ya I do have a vent tube at the top of the dome but not rendered a shell yet. What you see is the lower portion of p-crete being slightly more cementy to aid in applying to the vertical surfaces. And I smoothed it out more. I’m going to render with a stucco and then mosaic tile to finish but I will wait till I see no more moisture! I was cooking a bunch of pizzas in it tonite and noticed steam still rising from the vent so I assume that was the problem. But I guess I’m just gonna try and fill the cracks and see what happens. Has anyone tried this before?

[david s]

Hi Dave,
I understand now. Because you’ve added more cement to the verm mix it fills more of the spaces between the grains. This makes it more difficult to remove the water. As you’ve said the cracks are not in the inner brick dome those cracks in the vermicrete don’t matter. The crack in the brick arch however should be filled. Use a mortar with very fine sand by sieving some and dampen the crack well before attempting to fill. Maybe grind out some of the existing mortar as well. Keep the area damp for a few days. Then proceed to dry the oven out completely and gently with more fires. Throwing some plastic over the oven during firing will tell you when it’s dry because the water will condense on the underside. Once the water has been purged proceed with the rockwool and outer verm layers.

[Killeraye]

Ok great. Thanks David. I have fine silica sand already. I even have some powdered silica but that might not give it enough structure? I’ll show my work/results. Where should I post my whole build?

[david s]

Go to Pompeii oven construction in the main page and select +new topic and put your stuff there. That becomes your thread until highjacked by others.

[Kvanbael]

cracks are not in the inner brick dome those cracks in the vermicrete don’t matter. The crack in the brick arch however should be filled. Use a mortar with very fine sand by sieving some and dampen the crack well before attempting to fill....

Is that the general consensus, that dome cracks are better filled?
I have two vertical dome cracks, one in front (including my arch) and one in the back. Along those cracks, some joints have opened up 1mm or more. No structural issues (eg. loose bricks or smoke escaping) and no issues with performance. But if filling the cracks will prolong the oven's life, then I'll better get at it, I suppose.

[david s]

Filling the cracks in the inner dome is usually not very successful, they often just reappear. I think the consensus is to leave them. All ovens have cracks.If it’s in the outer arch or outer shell then it’s and entry point for water to get in as well as being cosmetic.