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pikemonkey 03-24-2014 02:26 AM

My First (hopefully last) build - Cast Refractory
 
4 Attachment(s)
So I finally managed to get going on this project.



Attachment 41808

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.
Attachment 41809

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.

Attachment 41806

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

Attachment 41807

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 03-24-2014 05:52 AM

Re: My First (hopefully last) build - Cast Refractory
 
Lookin' good !!!

Greenman 03-24-2014 06:09 AM

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 03-24-2014 02:29 PM

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

Originally Posted by pikemonkey (Post 171155)
So I finally managed to get going on this project.



Attachment 41808

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.
Attachment 41809

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.

Attachment 41806

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

Attachment 41807

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 03-24-2014 03:40 PM

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 03-24-2014 10:43 PM

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

Originally Posted by pikemonkey (Post 171204)
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 03-25-2014 12:09 PM

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 03-25-2014 01:07 PM

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 03-25-2014 02:49 PM

Re: My First (hopefully last) build - Cast Refractory
 
4 Attachment(s)
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 03-25-2014 04:15 PM

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?


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