Dome mortar joint crack after curing fires, advice needed

[JTM91]

Hi everyone,

I’m building a Pompeii-style brick oven and I’m looking for some advice before I go any further.

The oven has an internal dome diameter of about 1 metre. The dome is built from firebricks with refractory mortar from a wood-fired oven / refractory supplier in NSW.

The crack is in the dome wall, in the mortar joint between the bricks. The bricks were soaked before laying.

Build details:

• Pompeii-style brick dome oven
• Internal dome diameter: about 1 metre
• Firebrick dome with refractory mortar
• Mortar was supplied by a wood-fired oven / refractory supplier in NSW
• Concrete support bench is about 120 mm thick
• Under-floor insulation is calcium silicate board, either 25 mm or 30 mm thick from memory
• Dome has not yet been wrapped in ceramic fibre blanket
• Dome has not yet been rendered with perlite render
• The dome was fired while still exposed/uninsulated

I’ve done about five curing fires. The first one was around 150°C maximum, then I increased each firing by about 60°C. The last fire got to around 450°C.

To be honest, I fired it before insulating the dome because family and friends were putting pressure on me to use the oven, and I probably pushed ahead before the oven was really ready.

The crack started at around 1 mm and has now opened up to about 4 mm at the widest point. It is in the mortar joint between the dome bricks. I’ll attach photos showing the crack from the inside and outside. The crack starts at the soldier course and runs upward however the peak width is around the solider course/layer 1 and 2.

The oven hasn't been fired since I noticed the expansion of the crack to roughly 4 mm which was around 9 months ago, the crack hasn't expanded since. I should also note that I did notice smoke leaking from the crack, smaller smoke leaks were also detected on a much smaller crack on the other side of the dome.

My main concern is whether this is just a normal curing/mortar joint crack, or whether it means the dome is spreading and I should reinforce or repair it before insulating and rendering. Is this build savagable?

I’ve read online about people using a stainless steel band around the soldier brick course to restrain outward movement. I was wondering whether that is worth considering here. One idea I had was a stainless band around the soldier bricks, possibly connected to steel brackets or supports fixed into the 120 mm concrete support bench. But I’m not sure if that is a good idea, overkill, or potentially a bad idea because of thermal expansion.

My questions are:

1. Is this oven salvagable?
2. Is this stainless steel band around the soldier course a real solution, I'd prefer to over engineer than to have any doubt of collapse

Here is a link including a video to an earlier post I made on reddit https://www.reddit.com/r/pizzaoven/c...my_pizza_oven/

Any advice would be really appreciated!

[JTM91]

Well I didn't get any replies but I did get some advice from a local supplier (Wood Fired Oven Co in NSW) that I'll share here in case anyone else can benefit from it.

The main issues was firing the oven prematurely without the ceramic blanket and external render, secondly refractory mortar should not be used for gaps wider than 4mm.

The solution currently will be:

1. grind down the mortar where the cracks appear and in large mortar gaps, and use a 1:3 mix of fondue cement and sand to fill those gaps from the outside and cover the whole dome in a 5mm layer of the same mix
2. cure the oven again to dry out the fondue cement
3. use air set mortar from the inside of the dome to fill in any gaps
4. wrap the dome in ceramic fibre blanket and perlite render

[david s]

Once the cracks are there repairs are usually not successful, but as you are not finished you might as well give it a try. You are correct to conclude that firing it while uninsulated is the cause. Because it’s a dome it will not collapse. Steel bands are sometimes used for ovens with low domes and vertical first soldier courses, but if yours is the more stable full hemisphere steel bands won’t really help.If the cracks are already there a parging thin layer will do little to prevent the dome from expanding at the point of the cracks. Probably better to fill the cracks from both the inside and outside, leave it for two weeks, insulate then do the drying fires and finally outside render.
There are two kinds of oven owners. Those who say their ovens have cracks and those who lie about their ovens having no cracks.