My First (hopefully last) build - Cast Refractory

[pikemonkey]

So I finally managed to get going on this project.





Built the base from a stash of block paving I had.
Used a rack 100.x 65 x 1,8m lintels and topped off with a 2" layer of vermecrete.
3" of Calsil board laid on this and a dome of sand and bricks built for the form.
Used a plywood/MDF form for the archway.


Form was then coated with newspaper - this was a pain since the wind kept blowing it away, no matter how wet the newspaper was. Eventually I held one sheet in place and stuck the next sheet to it using PVA glue. Worked around the form "wallpapering" it like this and that worked just fine.

A 4" thick layer of refractory castable (1400) was then applied and patted into place. The sand dome had been kept moist and was reinforced with bricks inside so it could put up with a good slapping!
Mixing one bag at a time and putting down layers of castable, 4" wide and about 1" thick. Working round the dome for each "course" so I could keep an eye on the thickness as I progressed to the top.



I'm not a builder, or a plasterer, so quite proud of the result.



Curing fires in progress - verry satisfying. No cracks on the first two, but managed to get a couple of hairline cracks on the third. I could see the steam coming out.
A touch disappointed, but from what I've read - these cracks should not be a problem.
I'm a novice who's made a 4" thick single casting from refractory concrete - reckon I would be very lucky to miss out on any cracks.
Still working on a wooden form for the flue arch.

Looking at a sunny day today with poor weather for the rest of the week, so I plan to cover the main dome with 2" insulation and 2"vermecrete today.

[jeeppiper]

Re: My First (hopefully last) build - Cast Refractory

Lookin' good !!!

[Greenman]

Re: My First (hopefully last) build - Cast Refractory

Looks good, congratulations. Plenty of good things built by first timers with 'learn as you go' skills.

[david s]

Re: My First (hopefully last) build - Cast Refractory

So I finally managed to get going on this project.



[ATTACH]41808[/ATTACH]

Built the base from a stash of block paving I had.
Used a rack 100.x 65 x 1,8m lintels and topped off with a 2" layer of vermecrete.
3" of Calsil board laid on this and a dome of sand and bricks built for the form.
Used a plywood/MDF form for the archway.
[ATTACH]41809[/ATTACH]

Form was then coated with newspaper - this was a pain since the wind kept blowing it away, no matter how wet the newspaper was. Eventually I held one sheet in place and stuck the next sheet to it using PVA glue. Worked around the form "wallpapering" it like this and that worked just fine.

A 4" thick layer of refractory castable (1400) was then applied and patted into place. The sand dome had been kept moist and was reinforced with bricks inside so it could put up with a good slapping!
Mixing one bag at a time and putting down layers of castable, 4" wide and about 1" thick. Working round the dome for each "course" so I could keep an eye on the thickness as I progressed to the top.

[ATTACH]41806[/ATTACH]

I'm not a builder, or a plasterer, so quite proud of the result.

[ATTACH]41807[/ATTACH]

Curing fires in progress - verry satisfying. No cracks on the first two, but managed to get a couple of hairline cracks on the third. I could see the steam coming out.
A touch disappointed, but from what I've read - these cracks should not be a problem.
I'm a novice who's made a 4" thick single casting from refractory concrete - reckon I would be very lucky to miss out on any cracks.
Still working on a wooden form for the flue arch.

Looking at a sunny day today with poor weather for the rest of the week, so I plan to cover the main dome with 2" insulation and 2"vermecrete today.

Visible steam is an indication that you are proceeding too fast. if your dome is cast in one piece you will get some cracking, but don't worry they won't get any worse and your oven will perform like a champ for years.it should outlast you.To build the flue gallery you can fill the entry with sand and form your mould there to trowel your mix over.

[pikemonkey]

Re: My First (hopefully last) build - Cast Refractory

Cheers chaps.
I saw some previous posts from David S where he cast a flue arch about 1" thick (I think) so it would heat up quick for good draw. This was part inspiration for my making a separate arch.
I am using refractory castable which recommends a minimum thickness of 2", but can I go thinner with reinforcement?
I have not got s/steel needles, but do have some offcuts of armoured electrical cable in the shed.
I was thinking of stripping the armour wire, which is stainless steel strands (dia 0.5mm ish), and laying lengths of this into the cast.
I would be grateful for anyone's comments on this.

[david s]

Re: My First (hopefully last) build - Cast Refractory

Cheers chaps.
I saw some previous posts from David S where he cast a flue arch about 1" thick (I think) so it would heat up quick for good draw. This was part inspiration for my making a separate arch.
I am using refractory castable which recommends a minimum thickness of 2", but can I go thinner with reinforcement?
I have not got s/steel needles, but do have some offcuts of armoured electrical cable in the shed.
I was thinking of stripping the armour wire, which is stainless steel strands (dia 0.5mm ish), and laying lengths of this into the cast.
I would be grateful for anyone's comments on this.

My thin cast is basically to save weight and material as well as reducing thermal mass because the gallery can act as a heat sink, but I guess it must heat up a bit faster too.
If you are making a thin cast then I think the reinforcement is more important. I also cast in some buttresses on the sides to increase strength so I can keep the casting thin. If you don't have access to stainless needles I think the 0.5 mm stainless wire should work ok although placement may be difficult. I'd be inclined to try stripping the wire and cutting it into one inch lengths with some bolt cutters. You should be able to cut around 20 wires in one go. Anything much longer than this length creates difficulty in placement.

[Wiley]

Re: My First (hopefully last) build - Cast Refractory

Only suggestion would be to hunt up a cable cutter rather than using bolt cutters. They are different in that cable cutters shear and the bolt cutters pinch the cut making the job much easier/quicker and the cut ends cleaner.

Another possible source for stainless cable is used stainless steel halyards from a local boatyard should you happen to live near one. I would think 7x 19 cable would be more suitable than 1 x19 (usual standing rigging on a sailboat is 1x19) as the strands are be smaller in diameter. I would also think the slight twist would aid in the holding power over straight needles. All wire or wire/rope halyards are replaced on a regular basis as they develop "fish hooks" which are broken strands that bend over forming hooks... nasty on hands.

Hope this helps,
Wiley

[pikemonkey]

Re: My First (hopefully last) build - Cast Refractory

Thanks again guys.
Actually I work on ships, plenty of wire there, but when I'm away at work, I'm nowhere near home or the oven, Off to work next week, so the clock's ticking on this project.

I might revert to a 2" or 3" casting instead for the vent arch now. It;s not a moblle oven and weight is not a concern. I have 3 x 25kg bags of castable left - should be more than enough. Plus not sure if I want to take a chance and mess it up. It's not the castable, it's the delivery cost for more!!!
The other reason is I've been looking into vent design. I can find details on brick arch vent sizing, but nothing for castable
I have managed to scavenge some 7" flue pipe.
My vent arch is internally 2" higher than oven opening. Is this ok?
(changed this from 1" just for a little more headroom)
Should I cast the vent arch to include "sweep"/ "gatherer" or "cowell" up to the flue pipe. (terminology meltdown!!!).
I'm seeing about 12" x 6" for similar brick chimneys.

[david s]

Re: My First (hopefully last) build - Cast Refractory

These pics may help you. This is my solution. There are no doubt many other ways to do it.
Hope it helps, a picture says 1000 words.

[pikemonkey]

Re: My First (hopefully last) build - Cast Refractory

That's perfect Dave.
My form needs reworking a bit, but I'm on the right track then.
I've seen previous posts mention Vermicrete as a thermal break between dome and arch. Is this plain old vermiculite and Portland cement? Or vermiculite and homebrew?
I also have some fire rope and offcuts of calsil, insulation blanket, not sure which is best for this. I would guess vermiculite be the safer bet near food?

[david s]

Re: My First (hopefully last) build - Cast Refractory

In my case, because my flue gallery is so light I join it to the dome with refractory mortar and have a thermal break between the gallery and outer arch where temps are not as high, but you can place it between the dome and flue gallery if you wish. I use 4:1 (vermiculite, cement) vermicrete for this. Having the thermal break a bit elastic allows for some thermal expansion.

[brissie]

Re: My First (hopefully last) build - Cast Refractory

Your oven is looking good. I did a cast refractory oven also. Its not as refined as David s's casting, but it does the job. Its about 2 inches thick in most parts, but thicker on the sides and thin next to the dome entry.

For the join to the dome I used a mix of sieved castable and vermiculite 5:1 first, but it started to fall to pieces, and replaced this with ceramic rope encapsulated in a sieved castable slurry. You want to minimise exposure to ceramic fibre.

I would be careful if your fire rope is not ceramic fibre. lots of glass fibre rope about, buts its only rated to 350 degrees. Ceramic is rated much higher. With fire coming out or the dome entry, it could get above 350 degrees.

The sieved castable and vermiculite 5:1 might work for you, but I moved the outer flue gallery accidentally during construction, and from that point on I had problems with it. The protected fibre rope did the trick.

My build at your stage of construction:
http://www.fornobravo.com/forum/51/n...e-19976-8.html


Cheers,

[pikemonkey]

Re: My First (hopefully last) build - Cast Refractory

Thanks David and Brissie,
I'll have to check what rope it is.
I do have some offcuts of body soluble blanket.
Some will be used over the vent arch, and I was planning to tuck a bit between arch and dome anyway, then shield it at the inside of the arch with vermicrete. (i could use some sifted castable)

Managed to get the blanket and vermicrete on the dome two days ago.

2" blanket all over, then I had enough to lay another 1" over the top from from to back (dome had a mullet hairdo)
Slapped about 1 1/2" vermicrete over that.
Fired it up yesterday - gentle fire for about 3 hours.
With no door and only a rain cover through the night - inside walls were still warm this morning. Only about 25degC (measured by touch), but gave me something to smile about.
I really can't wait to get a full burn on this.
I've had 6 curing fires so far, two since I put the insulation on. I suppose I'm going to need a few more when I fit the vent arch.

[pikemonkey]

Re: My First (hopefully last) build - Cast Refractory

Cast the arch yesterday.
I beefed up the design a bit and have about 1/2 a bag of refractory castable left.
If I sift this and don't have enough mortar for the thermal break, can I add a bit of fireclay to bulk it up? I have about 10kg of powdered fireclay.

[david s]

Re: My First (hopefully last) build - Cast Refractory

Cast the arch yesterday.
I beefed up the design a bit and have about 1/2 a bag of refractory castable left.
If I sift this and don't have enough mortar for the thermal break, can I add a bit of fireclay to bulk it up? I have about 10kg of powdered fireclay.

Yes, just replace the equivalent volume of aggregate removed, preferably with half sand and half powdered clay. Remember that too much clay in the brew means more shrinkage and therefore cracks.