My first build - a catalogue of cock-ups :(

[_Ed_]

Hi all,

I've just finished the dome on my first oven, and have started the curing fires. I'm using heat logs which have a really low water content but the oven is still getting really smoky, like a thick layer of smoke just above the wood which makes me think it's not combusting properly? I did read/watch a lot of guides before starting but clearly some of the information didn't go in as now I look at the oven and compare it with the info I think I've made 3 major errors (other than the appalling brickwork)

• The dome is way too high - I can't measure it right now because it's still hot inside the oven but measuring from the outside it's around 25" up to the top, and possibly even higher than that. I don't quite understand how that happened because I was using a trammel to set the angle of the bricks and I followed it pretty well (or so I thought). The floor is 36" across so the dome should be 18" high, right?
• The arch is too low - I bought the door you can see in the photo before buying anything else and kinda planned backwards from there. The door is only 9" high though, meaning my arch to dome ratio is way way off.
• The flue opening isn't big enough - Again, I don't know how I missed that every design and photo of a good oven has a sweep up to the flue pipe instead of just a hole like I have. It is drawing smoke up but clearly not very well.

Is there any remedial work I can do to try and improve the performance of the oven? We're probably moving house within the next few months so knocking it all down and rebuilding it isn't an option really, but it would be nice to get some decent pizzas out of it before we go! I was thinking I could grind out more of a vent opening towards the dome so it captures more smoke, will that weaken the arch too much?

Any advice would be really great, as I'm feeling quite down about the whole project at the moment!

Thanks

[UtahBeehiver]

To bad you did not get with us earlier in the build but what done is done. So here are a couple suggestions or observations.

1. New ovens are typically smokers due to the water in the mortar, vcrete, etc. It get better as the oven dries out.
2. The vent opening, as you noted, is very small, and angular. The square inches of the opening should be at least the same area as the chimney pipe. I would take a angle grinder and take off some of the angle on the bottom side to smooth out the flow to the chimney pipe. When starting a fire, build a top down fire right under the vent opening to get a good draft going then push into dome once the draft is going.
Be really careful not to cure too fast and too hot. Curing takes time.
PS I cannot tell if the oven is insulated or not but it should be before you cure.

[_Ed_]

Thanks for your quick reply!

Yes I would have liked to do a bit more back and forth with the forum but our house move came quite unexpectedly and Mrs Ed didn't want to pay the movers to take a ton of firebricks to the new place so I just had to throw this together as quickly as possibly. Luckily I went with a smaller size than planned so I will have some unused bricks to take to the new place for WFO mkII.

The flue opening is just slightly smaller than the pipe - I went for a 6" diameter flue (I suspect I should have gone with 8"?) - but I'll definitely grind out the opening a bit more so it acts as more of a funnel, like you suggest.

The dome wasn't insulated in that picture but between now and then (the fire in those photos never got the dome hotter than 60C before I gave up) I have insulated it.

I hear you with the curing - I was aiming to do 4/5 hours at 75-100C tomorrow, and then go up to 125-175 the day after, and so on. Is that too ambitious?

With the dome being almost certainly too high is that going to make cooking a decent pizza very difficult?

Thanks again, really appreciate the advice.

[UtahBeehiver]

What did you insulate with? Ceramic blanket or Vcrete, if the latter, there will be a ton of water to get rid of so it will take quite a bit longer to cure the oven. IMHO, I think you will be fine with a higher dome, it is the shape of the dome the helps radiate the heat down. If you find the bottom cooking faster than the top then you can do what is called "doming", you raise the pizza off the floor towards the dome with the peel, kind of like broiling in an oven. You will just have to experiment when that time comes. To ensure you are not curing to fast, if you see steam coming off the oven then you are too hot. David S suggest placing a piece of plastic over the dome and watch for water condensating under the plastic, once you no longer see then the dome is dry. Also the a black ring around the bottom of the dome indicates the floor insulation is still wet.

[_Ed_]

I used blankets for the dome, and some loose vermiculite in the space around the flue pipe where it sits inside the chimney, which I assumed would help it draft a bit better?. I love the suggestion of putting some plastic over the top to check for condensation, what a great idea! I laid the Vcrete for the floor last year so at least I don't have to worry about that being wet...

[david s]

I used blankets for the dome, and some loose vermiculite in the space around the flue pipe where it sits inside the chimney, which I assumed would help it draft a bit better?. I love the suggestion of putting some plastic over the top to check for condensation, what a great idea! I laid the Vcrete for the floor last year so at least I don't have to worry about that being wet...

You can also use a garden moisture meter. If you have vermicrete over the blanket it will look pretty dry on the surface after a few days, but you can be sure that it will have plenty of moisture deeper in. If you've not used vermicrete, but only loose vermiculite then you can ignore this advice.

[_Ed_]

I have filled a few gaps with vermicrete (had enough blanket for 1 full layer and nearly all of the 2nd layer) - if I keep the curing fires at a pretty low temperature will that help dry it out, or should I let it dry out completely naturally? Bearing in mind I'm in London so the weather for the next few weeks will be cold and damp (the oven is under cover though, so won't be being rained on)

[david s]

The normal regime is 7 fires in 7 days getting progressively bigger and longer until the black soot has completely Burt away. Then you can do the cement render for the outer shell. I then wrap the whole oven up in cling wrap to hold the moisture in the outer shell to enhance its strength. Leaving it for a week before unwrapping. Some folk use chicken wire to reinforce this layer, I use AR glass fibres randomly added to the mix. If you chase around you should be able to find a commercial render that already has them in the mix.

[_Ed_]

Ah I've already done the first layer of the external render (with the chicken wire)... From reading guides I saw that the curing fires needed to be done after the insulation was put on the dome, and I kinda assumed the render over the insulation was part of that. In which case I guess I'll leave that first layer of render, do all the curing fires, then do a final skim with the clingfilm wrap? I didn't realise you could get a render with fibres in them for strength, I was just using sand:cement:lime in a 4:1:1 mix.

[JRPizza]

More advise for the next oven, if that is still in the plans. It looks to me like the door might be in the wrong place if you want to maximize the time to do any retained heat cooking. A properly placed door seals against a "reveal" on the inner arch and separates the oven chamber off from the outside, including the chimney/vent area. Some builders that have placed the door where yours is find a way to block off the chimney, but you are still losing heat to the vent area that could be used for cooking.

[david s]

Ah I've already done the first layer of the external render (with the chicken wire)... From reading guides I saw that the curing fires needed to be done after the insulation was put on the dome, and I kinda assumed the render over the insulation was part of that. In which case I guess I'll leave that first layer of render, do all the curing fires, then do a final skim with the clingfilm wrap? I didn't realise you could get a render with fibres in them for strength, I was just using sand:cement:lime in a 4:1:1 mix.

If the drying fires are done after the render, not only is it more difficult for that inner water to escape, but the trapped water can crack the outer rendered shell because steam creates some high pressure as it expands. So it’s even more important in your case to tease the water out slowly. This is extremely difficult because you are in a position so close to completion that encourages you to hurry up and get it done. Try to resist this and forget about pizza temperatures for now. You can use the heat to roast a chicken or something at the lower temperature.

[_Ed_]

More advise for the next oven, if that is still in the plans. It looks to me like the door might be in the wrong place if you want to maximize the time to do any retained heat cooking. A properly placed door seals against a "reveal" on the inner arch and separates the oven chamber off from the outside, including the chimney/vent area. Some builders that have placed the door where yours is find a way to block off the chimney, but you are still losing heat to the vent area that could be used for cooking.

Yes the next oven will definitely have a proper inner door! I was initially hoping to still do a separate inner door, but when the plans changed from "take your time with the build" to "this needs to be built before you move house" I gave up on it and bodged together the present monstrosity.

Something that really held me back with doing what I wanted to do was finding a quick way to cut bricks. I couldn't find a diamond blade for my mitre saw so I was stuck with a reciprocating saw with brick blade which was real real slow. What do most people use to do quick and accurate cuts on their bricks?

[_Ed_]

If the drying fires are done after the render, not only is it more difficult for that inner water to escape, but the trapped water can crack the outer rendered shell because steam creates some high pressure as it expands. So it’s even more important in your case to tease the water out slowly. This is extremely difficult because you are in a position so close to completion that encourages you to hurry up and get it done. Try to resist this and forget about pizza temperatures for now. You can use the heat to roast a chicken or something at the lower temperature.

Thanks for the heads up. We were actually hoping to get it fired fully after the weekend but I can see this is a bad idea so I think I'll just finish the dome renders then we'll be away for a few weeks over Christmas, then pick up with some more cautious firings in Jan.

[JRPizza]

I think quite a few of use have used a 10" wet diamond saw. I got mine from Harbor Freight but I see the prices have gone up considerably since I bought it. If you poke around here on the forum you can see what other builders have used to cut their bricks. There are some low tech low cost methods that would probably beat the heck out of a reciprocating saw. If you can find a used wet saw I would recommend it as they do a very good job - accurate, repeatable, and with the relatively slow blade speed and smooth blade I never felt like I was in danger of losing a finger.

[Chach]

Some have used a diamond blade in a miter saw. I did this before it works but it’s very dusty.

Ricky