36" Pompeii Dome - Thailand

[danhem]

Caveat Emptor, this is where we see a lot of builders get impatient. They cure their ovens too fast and too hot and crack them. The turtle wins the race in curing. You can start with charcoal briquettes (cook something while you at it) maybe a couple times. This heats the oven to about 200-250 F, then really small fires, one extra piece of wood can really spike the temp on the dome almost immediatedly. If you are seeing steam, you are running too hot too fast. David S suggest placing plastic over the insulated dome and if their is condensation forming then oven still is wet.

I am setting some small fires and have slowly built up to 300F. Even getting to that temperature with charcoal briquettes and some small strips of wood has been a challenge. All my wood is damp so even if I wanted to push it higher I'm not sure I could. Also the underfloor ceramic FB is wet. The weep holes under the hearth have been weeping, it's a real fight to keep the rain out and the oven was left uncovered whilst being hit by an unexpected downpour. i am covering the oven with tarp when the rain comes and uncovering as soon as it passes. If the trap is on for a few hours, a lot of condensation builds up.

Question is - Is it even worth battling again the wet weather right now with daily fires getting the dome apex to 300F? Should I try to push the heat further or set some low fires for a long period?

[danhem]

Still working through the curing process with small fires, raising the temperature every second day and setting a longer fire maintaining the temperature. Up to 600F now and maintained that for around 3 hours today. I checked the temperatures 3 hours after letting the fire burn out and it seems that the brick temp retention decreased by around 50% from their peak.

At 600F the outside dome (with 3" FB insulation) showed no signs of heat loss and the under hearth temp did not increase either. The under oven floor fibre board exposed at the front of the vent landing is still damp and I have no way of knowing how damp the rest of the FB is.

I'll aim for a short burn at 700F tomorrow followed by a longer 700F the day after. I'm hoping that these longer burns are help to dry out under the oven floor.

I have a hairline crack in the outer arch during the fire but this all but disappears once cooled. Not a nice sight to see at first but I'm putting it down to an expansion crack at this stage.

The fire to reach 600F dome apex temp was pretty impressive to watch. Seems that to get to 800f/900f the fire will have to be a monster.

[UtahBeehiver]

At some point you will see the dome clear of carbon and work its way down. If you see a black ring around the bottom it is an indicator that the floor insulation is damp.

[danhem]

Have reached the dizzy heights of 700F in my curing program, yet to see the carbon clear but hoping this will happen as I raise the temperature. It's definitely a nervous time wondering if something will go wrong but without tempting fate the situation is so far so good.

I recorded some heat under the hearth, which I'm happy about as the under floor insulation got very wet. The heat drain through the weep holes are perhaps telling me that moisture is being driven out. Also recorded a very slight temp rise on the outside of the oven dome and walls. Very small temperatures so not overly worried about that. I'm now considering the v-crete application after the next round of cures.

Managing the fire is a skill for sure, knowing when and where to position fresh wood can either make or break a good fire. I have employed a local wrought iron company to make an andiron to help with the fire management. Lumping a fresh log on top of burning logs has presented mixed fortunes for me - the new log either sets alight of it collapses the fire into a smokey mess. With the andiron I'm expecting new logs to sit with sufficient airflow as to avoid fire dampening and choke smoke.

Up to 700F with my fires and maintained the temp for a good 3-4 hours. Unreal amount of fun. Prepared a lasagne (4 hour ragu, hand rolled pasta, buffalo moz) and finished it off in the oven. A great moment and one of the most satisfying meals I have ever had. I may just attempt a pizza next week after a couple more curing fires, as the oven stands now the temperatures reached are probably a little low to cook pizza.

After letting the embers die down I believe I hit a stage of euphoria. I dont think I've ever seen colours like that.....maybe it was the wine...and beer.

[UtahBeehiver]

Wet floor insulation is the hardest to get out. As mentioned before when the dome clears and you see a black ring around the floor courses the oven insulation is still wet. Wet insulation also readily transmits heat so that is why you are seeing temp spike on hearth. You will actually, smell when the dome starts to clear, at least that is what Gulf and I have experienced.

[danhem]

Continuing to fire the oven and have now started to load it with fuel for higher temps. The upper dome bricks are clearing after an hour or so of intense fire and as others on the forum experienced, a distinctive smell comes off during the clearing. As UtahBeehiver previously suggested, lower wall bricks are not yet clearing so I have to assume that the under floor insulation is still wet.

Recording oven temperatures; after 2 hours of fire in the oven center my dome bricks seem to retain a temp of around 750F. After moving the fire to one side, the floor immediately records around the same 750F but quickly drops to around 500F. Clearly these temps are some way below what I am hoping to achieve.

During the fire the heat loss through the dome, walls and hearth is practically zero. However checking the temps this morning the hearth has spiked 30F as the oven has cooled overnight. Again I have to point to a wet floor insulation here, but find it strange that during the fire (fuel loaded burning for around 5 hours) the hearth heat drain records no spike in temp. The outer parts of the CF board insulation I can see appear to be fully dry. This remains a work in progress but I see each fire exactly as that, a little progress and a step in the right direction.

Good news is we got pizza out of the oven and it tasted as good as any wood fired pizza town . A couple of failed dough attempts over the past week after following recipes online revealed that humidity in the air here calls for much less hydration in the dough, as like-for-like recipes were coming out far too wet. I settled for a hydration of 57% with 00 Flour, and this seems to maintain sufficient water whilst proofing nicely overnight in the fridge. Just like the oven, the cooking side of things remains a work in progress.

[danhem]

The oven is getting better with each fire. Dome clearing nicely but still not getting fully clear down the walls and still recording around a 30F heat loss through the hearth on the following morning. Is this typical to lose heat down through the floor or is it that my floor is still wet? Strange that no heat loss is recorded during the fire.

Onto my the next steps now - v-crete the outside with one 1.5" layer before giving the oven (and myself) a rest for some time whilst the v-crete dries. I'll also look at finishing the front area off with a granite/tile surface.

I wonder if I'll ever get bored of watching the fire, something about it - man, fire, food. Great fun .

[UtahBeehiver]

As you said, the oven firing get better each time, just be patient.

[danhem]

Finally got the oven to the target temperature (900F Dome / 750F floor). It took a lot of wood to get there. The temperatures were retained for quite some time so was satisfied with the striking of that milestone.

On to the v-crete layer now and completed the first ring. Followed the recommended mix of 10:1 and added water to achieve consistency as explained by DavidS. David also recommends to throw in a hand full of powdered clay to make the mix more workable - I don't have access to the powered variety so left some kiln clay in water overnight to help dissolve and used that in the mix instead.

If I'm honest - I'd be absolutely amazed if the first ring sets with any degree of firmness. The mix is incredibly crumbly, and whilst I have read of similar here on the forum I just can't see at this stage how it will firm up with any kind of integrity. I hope to be proven wrong.

The ring is now covered in plastic wrap. I am guessing that I will need to leave it a day or two to firm up before progressing on to ring two. I am wondering how long to leave the first ring before deciding that the mix I used is good or not. I have a feeling that a 8:1 ratio of vermiculite to portland would be better but time will tell there I suppose.

[david s]

You will be surprised. After 24 hrs it will be firm enough. Doing a little as you've done then leaving it is a good idea as the higher you go the easier it becomes.

[Kvanbael]

What are your curing plans for the vcrete? Will you start all over again? Or is the vcrete not really adding a lot of water to the layers underneath?

[danhem]

What are your curing plans for the vcrete? Will you start all over again? Or is the vcrete not really adding a lot of water to the layers underneath?

Hi,

I will complete the layers then leave to dry under plastic wrap for a month or so. After that it will be back to low and slow fires. I will keep the vcrete later wraped in plastic during the fires and watch the condensation coming off. This seems to be a good indicator of how dry the layer is becoming.

Seems that the vermiculite soaks up a lot of water and it takes some time to dry it out fully.

i have followed the advice of DavidS on the curing processes and note that being over cautious with heat is the best way to go. I am petrified of overdoing the heat too quickly and then having to deal with the consequences.

Cheers,

danny.

[david s]

Danny, if you want the vermicrete to dry leave it uncovered. Keeping it covered holds the water in.
As you have already driven the water out of the inner dome there’s no need to hold the moisture in the vermicrete layer.

[danhem]

Danny, if you want the vermicrete to dry leave it uncovered. Keeping it covered holds the water in.
As you have already driven the water out of the inner dome there’s no need to hold the moisture in the vermicrete layer.

OK great, thanks for pushing me in the right direction.

The first ring of v-crete did set overnight. It's a very flimsy and light layer that could be cracked and broken down very easily, hardly surprising considering the structure of vermiculite itself.

I guess this layer isn't intended on adding any structural integrity to the build, more to act as another layer of insulation and a firm (firmish) base to stucco over. The stucco will likely set much harder over the v-crete adding strength the to eventual dome finish.

Completed ring 2 today and I expect that the remaining rings will be much easier than these first 12 inches or so. Tricky stuff to work with.

Thanks again,

Danny.

[danhem]

Once the V-Crete layer is complete, do I need to let it dry naturally or can I start to fire the oven again to drive the moisture out of the v-Crete.?

Other than letting the layer firm up for a few days I can’t see why some slow and steady fires will do any harm?

I don’t mind waiting a month or so for it to try naturally but would rather speed the process up if at all possible.

thanks,

Danny