castable refractory Newbie Forum Discuss castable refractory in the Good Background Information forums; Hi All, As with everybody else here, I seem to have spent ages reading about brocks and designs. I am ...

[stevepreece]

Hi All,
As with everybody else here, I seem to have spent ages reading about brocks and designs. I am utterly in love with the dmun's geodesic dome and edschmidt
castable triangles.

After much model, lots of paper cubes lying around, I am thinking of heading down the castable route. But, what castable should I use.I have searched for castable refractory and am presented with a variety of types. I am assuming I won't be wanting insulating stuff but which ones do I go for?

darleyrefractories dot com au (I can't post links) has 4 which are insulating and 3 high temp ones. Any advice anyone?

I plan to build a 90cm (36 inch) ,or there abouts, dome in the next 6 months.

Thanks
Steve

[dmun]

The nice thing about using industrial materials is that the manufacturers have process engineers on staff who's job is to answer questions just like this. These guy's jobs are pretty routine, and they often enjoy getting a question out of the ordinary. You should call Darley Refractories and say you have a technical question about a product. Explain the project, the thickness, the temperatures, the exposure to direct flame, and ask for a recommendation. Then come back and tell us what you learned.

[wild_willy]

Hi Steve
I am just at the last stages of completing a cast oven. I used Darley Densecrete 145 for casting the dome and it worked a treat. I also used their refractory tiles for the base which are 305 x 305. This determined the size of the oven floor at 915mm.
Happy to post more pics of the construction if you need.
Cheers
Willy

[stevepreece]

Sue from darley gave me this info.
To cast a dome, use the DC145.
Approx 8-10 bags will cast you a 1 metre diameter dome at 75mm thick

Now all I have to do get a dead tree removed from my garden.

[mr g]

Hi Steve, myself and a group of friends are about to embark on building four domes. Our plan is to build 100cm diameter domes but it has been suggested that we do it in four sections. This will make the dome easier to move and less chance of cracking. It has also been recommended that we use either stainless steel needles or chicken wire for re-inforcement. There are a number of suppliers and all sell roughly the same products.
It looks like we'll each spend about $350 for the castable.

Good luck with your project - if you have any other tips send them my way.

Wild Willy, some more pics would be super - did you use Cal-Sil board for the floor insulation ? Nice looking oven.

Regards
Mr G

[stevepreece]

Mr G

Cheers for the info.

I have memories of watching a Grand Designs episode, they were build a BECO house and used some kind of staple in the concrete mix as reinforcement rather than steel rebars.

Have you seen edschmidt's oven?
I did see another similar one on here but, can't find it again.

I will track your builds with interest.
Good luck.

Steve

[dmun]

It has also been recommended that we use either stainless steel needles or chicken wire for re-inforcement.

I'd vote no on the chicken wire. Castable refractory is ruinously expensive, very tricky to work with, and requires careful attention to curing and drying. Using a reinforcing material that will rust, swell, and cause cracks seems a false economy. Also, be careful with the stainless steel needles: They are called needles for a reason.

[wild_willy]

Originally Posted by mr g

Hi Steve, myself and a group of friends are about to embark on building four domes. Our plan is to build 100cm diameter domes but it has been suggested that we do it in four sections. This will make the dome easier to move and less chance of cracking. It has also been recommended that we use either stainless steel needles or chicken wire for re-inforcement. There are a number of suppliers and all sell roughly the same products.
It looks like we'll each spend about $350 for the castable.

Good luck with your project - if you have any other tips send them my way.

Wild Willy, some more pics would be super - did you use Cal-Sil board for the floor insulation ? Nice looking oven.

Regards
Mr G

Definitely dont need any additional reinforcement for the castable. It sets rock hard and provided it is of sufficient thickness it is very strong. I insulated my dome with 2 layers of ceramic blanket, then chicken wire then a layer of Perlite cement render. I will finish with a waterproof cement render.

Just got to the curing stage on mine and been firing over the last 3 days. Got the oven quite hot yesterday after a moderate fire all day. The top of the dome was just perceptably warm. Temp at the front of the oven ranged from 150-200C, I guess the temp at the lining surface was a lot higher. Certainly far too hot to touch.

Yes, I did use Cal-Sil board for the base insulation. This combined with 2 inch refractory tiles appears to be just adequate. I may add another layer of Cal-Sil as the suspended slab under the oven is getting quite warm. I would recommend at least 2 x 1 inch layers of Cal-Sil. Cooked some spuds last night. Oven is still very warm this morning with the door open all night.

Mr G do you want to see any specific details of my construction? I will post more pics soon.
Cheers
Willy

[mr g]

HI Willy, any pics would be good but particularly those showing how you set up the form for the dome. Did you make the dome in one piece or in sections?

Also, how thick is the perlite render?

Thanks.

[wild_willy]

Hi Mr G

I only had one bag of Perlite (100 Litres Fine) so that had to do. I figure it made about a 2 inch cover over the Ceramic blanket. Going on my firing of the other day, it seems that the dome top insulation is quite OK.

When I made the sand mould I made it on black plastic to protect the base tiles. It also had a short skirt (mini) that hung down around the edge to prevent the castable from adhering to the tiles so that I could remove them at a later stage if needed.

Cast the refractory concrete in one piece. Took 10 x 25Kg bags and just over 2 hours to do.

Pic of sand mould



Ceramic blanket


Perlite render