Questions on new build

[Gretsch]

I’ve laid down the insulation layer using Perlite mixed around 5:1. It took quite a few days to start to set, now it’s been a few weeks it seems pretty solid, lots of air pockets I didn’t count on while laying, basically was a bit hesitant to push down too hard in order to avoid the stuff breaking up too much but maybe the air pockets will insulate anyway.

I’m off to get the fire bricks, they’re 230mm x 110mm x 75mm, the 110 worries me a bit, should be 115mm hope it won’t throw out my layout, also says he supplies glue instead of high heat concrete, says it doesn’t crack under heat. My sister had one installed and they used glue too but it was one of those pre cast kits imported from Italy.

I’ve allowed dome thickness of 250mm being 110mm fire brick, 50mm blanket and 200mm brick render.

Made my IT and used it to scribe out the base template, internal diameter is 1060mm (round 42”).

Having trouble uploading photos at the moment, keep getting upload failed. Maybe images are too big ?

[Gretsch]

I've bought my supplies from Claypave in Old, appears Allan there has his own ideas on materials so I came away with some 450 x 300 x 50mm refractory slabs for the floor as you can see in the image I uploaded, big advantage is there won't be many cracks to impede the surface but I am concerned that it may not have enough thermal mass.

I also bought a bucket of Rylbond, it's a pre-mixed air set mortar to glue any face to face material, I was advised to stick down the slabs so they can't move sideways and potentially crack the oven walls.

I feel like taking the slabs back and swapping them for firebricks, then the question is has anyone used brick sand (the yellow sand) to mix with fireclay for the hearth bed or should I use washed river sand ?

I'd welcome any feedback on this from forum members.

[Toomulla]

there is no adhesive that will resist thermal expansion. so fine sand clay mix is fine I used the Rylbond on my dome with 1 to 2 mm joints and it worked well max joint is about 3 mm so tight joints are essentialI do not think there is any issue using the tiles for the floor it used bricks but believe the hearth insulation matters more

[david s]

I've bought my supplies from Claypave in Old, appears Allan there has his own ideas on materials so I came away with some 450 x 300 x 50mm refractory slabs for the floor as you can see in the image I uploaded, big advantage is there won't be many cracks to impede the surface but I am concerned that it may not have enough thermal mass.

I also bought a bucket of Rylbond, it's a pre-mixed air set mortar to glue any face to face material, I was advised to stick down the slabs so they can't move sideways and potentially crack the oven walls.

I feel like taking the slabs back and swapping them for firebricks, then the question is has anyone used brick sand (the yellow sand) to mix with fireclay for the hearth bed or should I use washed river sand ?

I'd welcome any feedback on this from forum members.

50 mm thick floor is fine and what most cast oven manufacturers use. Most oven manufacturers recommend the floor bricks or tiles be laid loose so that they can expand freely and individually as the bricks in the centre of the floor are going to get hotter and therefore expand more than the bricks at the perimeter. The larger the pieces are the more likely they are to crack. If laid loose any replacement required is simple. The sand/clay mix is just used as a leveller. Any type of sand will be ok but fine sand presents fewer problems if used as a leveller. If glued down it is far more difficult to replace a brick or floor tile. . Any gaps will fill with ash. Your choice but if it were me I’’'d be laying them loose. Everyone has their opinion, you could ask Alan how many ovens he’s built and fired.

[Gretsch]

I doubt Allan has built any ovens. He sells a small-ish barrel style pizza oven kit but has no idea on the pompeii design, he reckons the chimney goes inside the dome so there ya go.

Don't get me wrong he's a good bloke and has done me a good deal, so long as the floor will hold enough heat to cook everything I want (pizzas, ciabatta and roasts) I'll feel ok with the tiles and loose fit them. At least if one cracks I can replace it. It's going to be a bit of a job cutting the curved sides thou, I want this oven to be as good as I can make it.

[david s]

Curved cuts are easy enough with a 5" angle grinder fitted with a diamond blade.

[Gretsch]

Ive pulled up the Perlcrete layer in favour of the kiln insulation bricks I got. I just feel they’ll do a better job. Have laid and levelled the fireclay sand bed and hearth bricks. Today I’m cutting the perimeter bricks then laying the first course outside of them onto the insulation bricks.

Am I right the first course isn’t glued down ? And what about the arch base bricks?

[UtahBeehiver]

All of my first layer bricks (those sitting on the floor insulation) were free floating, ie no mortar. This gives the oven the ability to expand and contract and reduces chances of dome and arch joint cracking.

[CrabbaDabbaDoo]

Roughly how many bricks are needed for a build?

[Gretsch]

Depends on your size. There’s a spreadsheet you can download to work out your materials etc, works very well!
https://community.fornobravo.com/for...eet-calculator

[Gretsch]

Spent a whole day cutting bricks for the soldier course, keeping it low because I’m aiming to have the dome to a minimum height. So I cut the bricks to fit snug and mortared with Rylbond which is a pre mixed high heat mortar. Instructions say 1 to 2mm mortar otherwise it may not cure properly. I found that as I progressed, my constant tapping into place caused a bit of movement and had to force them together where the gaps opened a little.
Next day I noticed 3 or 4 places where it seems to have separated slightly. just wondering if I should do something about it now or if I leave it and go on. After all, it will probably crack some time in the future anyway.

Based in this experience think I’ll just mortar the rest the old way. Butt the faces and fill the gaps with home brew mortar mix. Cutting is a long process !

[Gretsch]

Well whole section came loose today, after taking it out I could see the glue hadnt completely gone hard so I put a fresh coat on and strapped it up. Hopefully that will put pressure on the joints and get a good bond.

Rylbond is an air set product and Im guessing the moisture in the bricks is keeping it soft.

I modified my IT to eliminate the thickness of the ply and the metal straps are secure compared to a floating ply sheet.

[Gretsch]

I cut the arch blocks yesterday, glued about 6 pieces then called it a day. That evening I was browsing through some designs and it struck me I hadnt cut my arch blocks correctly. Today I had a look at them and couldnt figure out how to make the cuts so I decided to just proceed and resign myself to cut the blocks to suit.

[SimonMALTA]

hi guys,

may i ask for advice, this is the closest topic i found re bricks cutting.

I was thinking of cutting the bricks in thirds instead of halves for the dome. i have some space limitations but do not wish to reduce the internal diameter and keep it 36 inches.

What do you think?

Thanks.

[Gretsch]

You could do that you’ll just have reduced thermal mass which means your heat won’t be retained as long but it will still cook.