Dome stayed up this time!

[Dutchoven]

Re: Dome stayed up this time!

Just an added bit with you guys about insulation. There is a product here in the US for ceramic fiber that makes it more rigid. It sprays on and you can shape the fiber, then once it sets it holds its shape. Don;t know if it has a practical use. Further on this issue I have to say that my most major mistakes in constructing my oven were to not give adequate respect to the expansion of the oven and by not insulating it enough. It is a good oven but the enclosure has cracks that have stabilized with time but I don't get a stable heat curve do to the lack of enough insulation.
Best
Dutch

[Bacterium]

Re: Dome stayed up this time!

thanks Dutch .....I'm thinking of firing my oven this Sat. as a check before I do the final render(stucco).
I think I have the blanket & perlite on correctly (after reading all the great advice on here) but this firing will allow me to check if there are any parts of the outer dome where it could be "leaking" heat.

Kiss4me.....doesn't it suck dealing with all the rain and cold at the moment? - I suppose its good for cement to cure though.

[RTflorida]

Re: Dome stayed up this time!

Dutch,
good point and exactly why I used 2" blanket on my oven. After talking with a local refractory specialist (who has built several precast ovens)
I decided the extra $$ spent on a thicker blanket would be a big benefit.
His thinking was the thicker blanket would absorb more thermal expansion of the dome, resulting in less potential for cracking of the ridgid exterior of the dome. Since my plan all along was to finish with mosaic tile, I certainly wanted to minimize the chance of exterior cracks........this would be of importance to those finishing in stucco as well.
I topped the 2" blanket with 3" of perlite concrete. Not a single dome crack and I have had the inside top of the dome over 1100 degrees. No rise in temp on the exterior....Good for my tile or would be for a stucco finish.

I think many of us have beat this horse to death, but it really can't be stressed enough. Insulate your oven until you either run out of money or your supplier runs out of insulating material. MORE MORE MORE

[KISS4me]

Re: Dome stayed up this time!

Yeah Damon, weather at the moment is not ideal for working outside. There is something bleak about working with wet cement on a cold damp day. Still we have seen off the shortest day and those in the northern hemisphere can get their share of the cold soon (by th eeather reports lots of areas could do with it!)

Point emphasised by Dutch about the importance of getting the insulation right is taken. Amazed to read that others ovens have 'leaked' after all these layers. I could put this down to poor workmanship, but this would be a bit rich.

Steve

[KISS4me]

Further progress - chimney

Quick update.

Found some time today to work on chimney. See photos attached. I hope it draws well as the vertical difference between dome opening and chimney opening base is greater than I was hoping.

Cheers Steve

[Dutchoven]

Re: Dome stayed up this time!

Kiss,
I think you will be fine. You might have some somke sneak out during your intial start up each time but you will get the hang of making a less smoky start. My oven puffs a bit of smoke out the outer opening once in a while but not too big a deal. Are you going to be using some type of flue liner in your chimney? Terra cotta or similar. Reason I as is that it might help that situation. The liner will be thinner than if you did a brick and mortar flue and would take less time to heat up and will therefore help the draw sooner. Just a thought.
I along with all the others here are happy for you and your oven. Your brick work is creative. I hope you keep that creativity with the items you will cook in that oven.
All the best to you!
Dutch
P.S. Youl will also see a smoke trail above the arched doorway due to the extra height but, that is only cosmetic!

[Dutchoven]

Re: Dome stayed up this time!

I know of one oven here in Mississippi that leaked after being built by Mexican masons. They built a very small oven(maybe 30" diameter), cut almost no bricks, and looks like they used only a standard mortar. It was then insulated with sand only and then an outer red construction brick dome. Several leaky cracks inside that when I saw suggested they use a high heat repair caulk to seal them. The outer brick work became horribly cracked. Insulation is important definitely but, they right insulation is the real key. That oven(the internal chamber) has to be able to breathe and to expand and contract with minimal connection to the exterior. If there is not enough room the oven will win. Thankfully I have no leaks(knocking on wood) other than some heat saturation issues that I have learned to deal with so the oven is safe. I was hoping to have the exterior temperature never get above 90 degrees when fully fired and saturated, sadly it gets about 25 to 30 degrees hotter than that. The good thing about it though when it gets cooler here in the fall and winter I have a bit of a patio heater as well as an oven. Remember when life gives you lemons, make lemonade and eat it with your wood fired pizza!
All the best!
Dutch

Yeah Damon, weather at the moment is not ideal for working outside. There is something bleak about working with wet cement on a cold damp day. Still we have seen off the shortest day and those in the northern hemisphere can get their share of the cold soon (by th eeather reports lots of areas could do with it!)

Point emphasised by Dutch about the importance of getting the insulation right is taken. Amazed to read that others ovens have 'leaked' after all these layers. I could put this down to poor workmanship, but this would be a bit rich.

Steve

[KISS4me]

Re: Dome stayed up this time!

Dutch

By a "using some type of flue liner in your chimney" do you mean an actual flue pipe inside the brick chimney leading to the vent at the top? If so what is the advantage of 'controlling the smoke'?

My plan was to gradually step in my brick work to a smaller opening and cap with a terracotta flue pot. Sounds like this may not be the best way to get best draw?

Steve

PS Thanks for your encouraging words about my progress.

[KISS4me]

Re: Dome stayed up this time!

Dutch
Yeah this was my thinking too. Based on the suggested chimney opening to oven ratio suggested on this forum I have elected for 2 pots. (that reminds me of the 2 pot screamer line). So no stepping in of chimney for me. See photos.

Have stucco/rendering coat over dome to do. I can almost smell that first pizza!

Seems that 3 stucco coats is the best way to go. I need some advice on the drying time needed between coats. My mail suggests that you need to leave a week between coats. This is tooooo long a wait for me. Planning to only leave a day between coats. Any comment on the consequences of 'rushing it'?

Steve

[Bacterium]

Re: Dome stayed up this time!

KISS4me the front section of your oven is looking great.

Talking about the stucco/render - I have just finished mine and with virtually no cracking (except for a small 1 inch spider crack in a section off the dome).........all due to the great advice on here. This thread was particularly helpful:
http://www.fornobravo.com/forum/f9/h...ender%2Fstucco

Ok, drying time.....from all the reading I felt it meant within 24hrs(between each layer).....no one actually said that. So here is how I did it (bearing in mind its winter here):

-Saturday afternoon first(scratch) coat - a 5:1 ratio (plasterers sand/portland GP cement). This was over my vermiculite coating that had chicken wire over the top....thickness was anywhere between 1-2inches. Once on I trowled it with a wooden float and then scratched it up .....see pics in my part2 posting

-Sunday late afternoon 2nd (brown coat) - a 3:1 ratio (sand/cement) + some oxide for colouring. Thickness was about half an inch. My mix was slightly drier so I used a steel float (carefully) to get the shape then I finished with a wooden float.....grabs like heck and is a bit tricky - texture was rough but even. Neill suggests detergent in mix....silly me forgets as I unload to wheelbarrow.

-Monday night, final coat.......its was freezing and rain was not far away. - a 2:1 ratio (sand/cement) + more oxide to get a colour like a darker sandstone. Thickness was about 5mm....I applied it with a steel float (carefully not to bring too much moisture up). Then about 2hours later I finished it with a damp sponge. I washed the sponge regularly (it wasn't dripping wet) so it didn't "drag" the coating around everywhere - yet it was wet enough to give me the slightly roughened texture I wanted. The sponge helped me smooth off any holes (to the layer below) yet kept the nice texture. Keep some mix spare to dab on any major holes.

I felt each layer had to "settle" so that before the next coat went on any cracking wouldn't transfer through (visually this was minimum 6 hours). Yet the previous coating couldn't dry or cure that way the next coating would bond nicely (within 24hours...approx.)
I learnt from the dome capping (under thermal blanket) that the cracking is apparent within an hour or so.....bearing in mind that was a brickies sand which moves a lot more as it want to settle down or bond whereas the coarsness of the washed sand can't really do that so much

I let the final coat firm up to Tuesday morning - the thing was carefully covered with tarps as it poured with rain monday night...about 2hours after I covered it. Sometime on Tuesday (can't remember) - I ditched the tarp and put some damp towels over it - these were kept damp until Thursday night.....This morning (Friday) coating is rock hard and no cracking anywhere on the dome. Did I fluke it (and it will crack in months to come???) or am I spot on guys!!!!!
Feel free to comment....so far I'm quitely confident

[KISS4me]

Re: Dome stayed up this time!

Thanks for detailed description of your 3 render coats Damon. The ?cracked stucco? link and your pics are great help. Your 'red gum roarer' is a great looking oven. I like the way it opens to patio area - must be pizza time for you soon!

Leaving only 24 hours between render coats sounds good to me.

Have include pics or my work today doing scratch coat (3 plaster sand: 1 cement). Unless someone on forum pipes up with good reason for not applying another coat in 24 hours I will apply ?brown coat? Saturday arvo. Fire up time is fast approaching!

Just curious. What is the advantage/disadvantage of wood over metal float in use and for finish?

Steve

[Bacterium]

Re: Dome stayed up this time!

no probs.....its a great feeling to get the last few coats on. I've done 10+ firings (after the curing fires) of my oven but I stopped part way through before I put on the blanket/perlite layers. Now I'm stopping the cooking for a few weeks to let all the render/blanket/perlite layers to settle/cure.
From the patio perspective.....It was pouring with rain a few weeks ago.....and I fired it up and could still cook pizza.

your render looks good to me - you are close to curing time, although its tempting to go full steam ahead the curing fires are important + it you gives a good excuse to sit outside watch it and have a beer....although it better weather for port or red wine.

The steel float tends to bring the water to the surface - more so if you go over the same spot a few times. It also gives a smoother surface, I liked the rougher texture of the wood to finish it off. The wood float is a pain to use as it sticks easy.

Here is a quick picture (at night) of my finished surface. It obviously wet but will give you an idea...... 4 full days and no cracks

[Hendo]

Re: Dome stayed up this time!

... it you gives a good excuse to sit outside watch it and have a beer....although it better weather for port or red wine.

Or, being 'brass monkey' weather - perhaps a Cooper's Stout!? P.

[Dutchoven]

Re: Dome stayed up this time!

I did not use a stucco coat but rather brick walls and a framed gabled roof so I do not have direct experience. I will say that I believe it to be very important to allow the highest percentage of moisture to get out of every layer of stucco before you do the cure. Any pockets of moisture will create steam and that will certainly cause cracking. Once again excellent job on the oven!
Best
Dutch

[Dutchoven]

Re: Dome stayed up this time!

Yes I did suggest putting a clay flue liner inside the brick chimney to the top. The reason it can help is since it is separate from the outer bricks by either air or insulation it(the flue tile liner) heats up faster than just the bricks(heating 1.25 inches of clay versus 2.5 inches). In some old chimneys I have had the chance to look into the interior of the chimney was lined with firebrick splits set on their narrow edge using purely firclay as the bond. In some cases of two sided fireplaces the entire flue ws constructed as one and then split by using a wall of standard firebrick set on the narrow edge to divide them into two separate flue. These were constructed before the use of clay flue liners like are available today.
Best
Dutch

Dutch

By a "using some type of flue liner in your chimney" do you mean an actual flue pipe inside the brick chimney leading to the vent at the top? If so what is the advantage of 'controlling the smoke'?

My plan was to gradually step in my brick work to a smaller opening and cap with a terracotta flue pot. Sounds like this may not be the best way to get best draw?

Steve

PS Thanks for your encouraging words about my progress.