House Brick Horror

[Hysteric]

Hey Guys this is my my "Budget" 42 inch build in inner west Sydney.

Plan was to build the entire oven with house bricks or other cheap materials as this isn't my place so I cant take it with me.

[dariusk]

Hey there Hysteric
Wow, I hope you are still planning to live there for a while to come after all the work you'll be putting in! Or it's a family members house so you can still visit after you move out... I have no plans to move anywhere for the next twenty years now I've started my oven!
Your stand looks great, I'm looking forward to seeing how it comes together
Cheers
Darius

[Hysteric]

Time to update my build:

My Brother in law turned up and decided to get the oven build moving. Thanks Bro!

[Hysteric]

Just need to figure out which way to go with the insulation and then its the dome
Jus

[david s]

select your bricks carefully. You need solid bricks not wire cut bricks full of holes. That may mean sourcing second hand old red pressed bricks. Depending on the clay composition they may hold up or they may not and you won't really be able to tell. Generally lighter creamy coloured bricks are likely to be more suitable. For the dome you should be able to get away with them, but the oven floor takes a greater beating so use fire bricks if you can afford them. Forty years ago solid creamy house bricks from Cooroy were discovered to be suitable for stoneware temps (1200 C+), lots of powers got some, I got a pallet of them to build a kiln, but i doubt they'd be available now.Attached are pics of badly spalled solid reds in fireplaces in Tasmania. I've seen the same thing in Victoria, but some oven builders in S.A. have reported good success with solid pressed reds. Sydney ??

[Hysteric]

I plan to use proper fire bricks for the floor. The 300 x 300 tiles.

Originally i planned to use clay commons I had lying around but on a trip to Tasmania i met a guy who builds pizza ovens and he told me he used Istra 40 from memory with just sand.

Istra isn't available in Sydney so I guess the alternative is refactory castable.

http://www.adelaidebrighton.com.au/a...A%2040_PDS.pdf

Said he'd built many and never had a problem. Its cheap too!

[Hysteric]

Time to get the oven moving.

I was thinking of going the vermiculite cement route for the underfloor insulation part.

Is 70mm enough thickness for this?

[UtahBeehiver]

IMHO, at least a 100mm of 5 to 1 vcrete under the floor bricks is needed.

[Hysteric]

Had to add an extra course of bricks to get the required height to give me enough room for the insulating component of my oven. Ended up with 130 mm total thickness. Should be more than enough.

For those wondering why i have left it 20 mm from the top is to get a nice flush finish with the oven floor and the outer finished level. The plan is to go with 50 mm bricks which leaves me with 30 mm proud finished level to which the outside tile can marry up to.

[UtahBeehiver]

If you can, be sure to drill a couple weep holes in the concrete hearth (maybe even come in from underneath) so any errant water can work its way out. Also, let the P/Vcrete dry as long as possible before you place the fire bricks on. P/V crete holds a lot of water so the more you can get out now the easier it will be to cure your oven later.

[Hysteric]

If you can, be sure to drill a couple weep holes in the concrete hearth (maybe even come in from underneath) so any errant water can work its way out. Also, let the P/Vcrete dry as long as possible before you place the fire bricks on. P/V crete holds a lot of water so the more you can get out now the easier it will be to cure your oven later.

Whats a sufficient length of time? Are we talking weeks or months?

What size holes would you suggest?

I was thinking 4 x 6.5mm.

[UtahBeehiver]

That is a sixty four dollar question on length, depends on your current climate, since you are in Southern Hemi, it is your winter now but you are in Sydney so a little more moderate. Do the best you can in drying it out and keeping any rain from getting on it. Should be okay with size and number of weep holes. This is important since you have the pcrete sunken in around a brick side wall. Water has a way of finding low spots and the weep holes will save you issues later on. I do recall that David S from NSW suggests a couple weeks.

[david s]

I did an experiment on drying vermicrete (attached) and it does take longer than you would think. It will eventually dry but as builders have reported that their ovens keep improving after months, i'd suspect that the damp underfloor insulation is the culprit as it is the hardest place to remove moisture from. Regarding the weep hole(s) attached pic shows how i do mine. The hole is actually square because i cast it 20 x20 mm, I glue some insect screen over it to prevent the vermicrete from falling through. A number of smaller holes should work the same.
Vermicrete insulating slab copy.doc.zip

[Hysteric]

Thanks guys. I went with 4 x 6.5mm holes.

I went with a 5-1 ratio with the Vermicrete and was quite surprised at how easily it compresses.So i sprinkled some portland cement on the top to give it some more surface strength.

Next time I think i will try 3 or 4 to 1 with the vermicrete.

Funnily enough i picked up some 230x115x50 fire bricks for the floor and when the discussion about what i put under them came up with the supplier the response was "You know that's not structural"

I told him i went with a 5-1 ration on the vermicrete and he said that it will collapse when the Portland cement burns out.

Really?

Did a quick search and came across this:https://www.delftclay.co.nz/how-to-m...ent-3-recipes/

3 different recipes for refractory cement.

Thoughts?

[UtahBeehiver]

It has only been a few days since you poured the vcrete so I doubt it has fully cured or dry yet. The trade offs of lower cement to vermiculite ratios is a higher thermal conductivity ratio. 5 to 1 has been used a lot on builds over the years and I have not heard of compression issues once the material has cured and "dried" out, again it vcrete holds a lot of water in it. Attached is a chart from David S showing the different Thermal Conductivity (K) for different ratios. You can see by changing the ratio to 3 to 1 from 5 to 1 the K values change by a factor of 4. IMHO, the Vcrete under the fire brick will not see the temperatures that causes concrete to burn out. The goal under the bricks with the vcrete is insulation not really refractory as the link in the last post suggests.