Advice required on preventing 3rd main chamber collapse

[Digga Don]

Karangi Dude
I have a couple of question around the metal support and insulation on your barrel vault.
I'm back on the horse after two traumatic collapses of my main chamber barrel vault. Both due to my error's , the first being plastic over the formwork which prevented the premix thin bed mortar Im using from drying on the inside in the Great lakes climate and insufficient buttressing. I removed the formwork, and it collapsed 3 hours later. The second arch which had a keystone flicked out from the skewback whilst I had temporary buttressing removed and excited with progress removed the formwork again. Whilst all the top courses where dry moisture and possibly frost had entered the mortar layer of skewback.

1 I was wondering if I should put a parge? coat over the main chamber with fiberglass render mesh or chicken wire in it to strengthen the whole thing?

2 I have installed steel supports on either side of the main chamber against the bricks with 0mm calcium board on the olutside.

[Digga Don]

I'm concerned about expansion of the steel and noticed your oven is the other way around. Im thinking i should change it?

i have pictures and a detailed drawing but i cant seem to attch them to post Any advice on that also

[UtahBeehiver]

Pictures can be attached using the "camera" icon in the upper left corner of the posting section. Pics are limited to 1.25 mg and about 5 per post. Karangi Dude, long time member, only visits periodically so it may be a while for a response.

[Karangi Dude]

Hi Digga Don, and Hi to you Russell
Don, as Russell said I only check in now and then but sending me a PM might get my attention as well
Don, it would be nice to see your photos so I can get a better understanding of your situation.
A low vault arch needs side buttress to support the downward thrust that is put on the walls by the weight of the arch, an arch will support itself but the sideways thrust has to be taken into consideration.
The outer steel that I used was to do just that become buttress, as this oven is on a steel stand that is almost 2 metres high I didn't want to build a brick outer shell for buttress, as you can see I used 50mm of fibre board then filled the void with vermicrete at 7 to 1.
Also building the side walls and the arch in bond certainly helps with strength.
Don I hope this helps you understand better and I look forward to seeing your photos also some sizing might help and a photo of the stand and the under hearth insulation
Cheers Doug

[Digga Don]

2nd build of arch, new form work, no plastic

[Digga Don]

Previous photo first build. Wrong caption fat fingers

[Digga Don]

Site of oven Cramps bay Great Lake

[Digga Don]

Site in winter to right of shed

[Digga Don]

Arch bricks Floor bricks 100 mm thick

[Digga Don]

Dry stacked at home on formwork version 1

[Digga Don]

Vermicrete slab 100mm on drystone base with gravel and rubble fill over boulder

[david s]

A few considerations,

If building the end walls against the barrel vault, there is a tendency for thermal expansion of the vault to push the end walls out. The structural integrity of the form is increased if the end walls are built under the vault and some of the lower course bricks tied in at the corners.

Also if the problem of collapsing barrel vault bricks was caused by the removal of the form, it could be because you haven't used wedges which are not visible in the pic of your second attempt. (or wedges of insufficient height) under the form so it can be easily lowered and removed without damaging the brick vault.

An oven built at ground level will be hard to operate and also will be prone to moisture wicking from rising damp.

[Digga Don]

Calci board 25 mm in previous photo under floor and walls. Main chamber arch on version 2 formwork with slats and vented supports.

[Digga Don]

Version 2

[Digga Don]

Version 3 completed today by adding last row either side and keystone. Metal buttresses inplace