Mr Gs Aussie Castable oven.

[mr g]

Re: Mr G's Aussie Castable oven.

Next was the experiment with the dome proper. There was lots of talk about casting in one whole piece, two pieces, even five pieces. In the end we decided four equeally sized pieces for the dome would be best both for the dome strength and ease of moving the pieces around (they weigh about 95kgs each). We cast the first two pieces of the dome by using a quarter dome form. This was tedious because we had to wait for the castable to harden sufficiently before we could take it off and move it around to the next quadrant. It took five hours to make the first two pieces.
I then covered the castable in plastic and left it to harden for a few days. The first two pieces looked pretty good but expected better results as the process was refined.
The pieces were quite easy to remove and they formed quite nicely.

[mr g]

Re: Mr Gs Aussie Castable oven.

Once the mould was finished I tried a couple of bags of castable just on the entrance to see how the process worked and whether the whole project was going to be possible. I used plastic cling wrap as a release mechanism. Mixing the castable was quite easy although it is obvious that it is a different product to normal concrete. I mixed according to the manufacturer's recommendation of 8%-10% water by weight and this was fine. The stuff looks like it is stiffer than it actually is. I belive the term is thixotropic - that is that it is normally quite thick but becomes runny when agitated. It was obvious as soon as I started applying the castable to the vertical walls of the entrance that it was going to slump to much so I quickly made up some forms for the sides. Once this was done I applied the rest to the upper part of the entrance with a trowel and that was fine. I used a vibrating tool on the sides and manually agitated the top part. This took me 45 mins all up. The first entrance was cast without a flue insert but subsequent ones all had a stainless insert that was 6" in diameter by 8" high. Once set and dried I was easily able to lift the entrance off of the mould. Overall I was quite satisfied with how it look although it could have been vibrated a little more thoroughly.

[mr g]

Re: Mr Gs Aussie Castable oven.

The sand mould had to be able to last for 10 castings so I made it as robust as was practicable. I decided that easiest and quickest way to toughen up the outer part of the mould was to simply apply some old acrylic paint I had lying around. four coats with 30 min drying intervals did the trick. Once it was dry it had quite a tough outer shell. I didn't want to mix cement in with the sand because I have another use for the sand once this job is finished otherwise I would have had a 1/4 cubic mtr of useless stuff that would need to be gotten rid of.

[mr g]

Hi, I thought I'd put my experiences down in one place for anybody interested in how I made my castable refractory oven. I have posts all over the place but it's hard find them all and fit them all together.
There were a couple of reasons I decided to build the oven out of refractory for in the beginning I was adamant that I would make it out of firebricks.
I thought that it would be time consuming and require me to get a tile saw which I don't own. The other reason is that I wanted some friends of mine to also build one and I knew that I was never going to get them to build one if it was going to be made out of brick since they didn't have the time/skill/inclination. So I made a sand mould at my place and we cast the domes at my house. We made 10 domes in around 5 weeks ie 2 per week.

Firstly I decided that we needed a 40" diameter oven which was a comprimise because a couple of the guys wanted smaller ones. The dome is 470mm high in the centre and has a door opening of 300mm H x 450mm W. I also cast a 25mm rebate for the door to sit against. The other thing that casting allowed me to do easily was make the entrance/landing area taper outwards to allow for easier access and visibility.

I used normal brickies sand to make the sand mould, the sand was damp and it was quite easy to work with and smooth into the right shape.