DIY Casting Modular Oven

[aiannar974]

Hello Everyone - I have been reading the posts about DIY cast domes. I see some people have cast in what looks like one piece even if it was done in more than one pour of refractory concrete and others have made a modular design. For me, this would be easier to handle and move to a base, however, I cannot see any comments or pictures that show how this is done. I have seen sonomacast posts on casting in sections, but this looks like it was done on one mold in sections and I am not sure what seperated the sections.

Any info would be appreciated.

Anthony

[david s]

You have to create something to separate the sections. In my case I've used fiberglass. foam rubber may be an alternative, so that you cast against it for one piece, then remove it and cast the next piece up against the previously cast section. But be really carefull to use plenty of release agent where the two castings join. To make a cast in a number of pieces is more trouble than it's worth for a single casting IMO. A one piece casting in situ over a sand form however, is a piece of cake. Large one piece castings are prone to cracking because of the uneven heating, but they are only minor and the thing won't collapse because of its form.

[aiannar974]

Hello David - Thank you for the info. The only reason I wanted to cast in sections is because I don't know how to move something 600 pounds or so up to a base.

Thank you,

Anthony

[wotavidone]

Single casting would be heaps easier, but the expansion cracking seems a worry. I have often wondered whether you could cast it in one piece, then mark it into your desired sections, and score to maybe half depth with a thin blade in an angle grinder. Then surely, if the heating caused it to crack, it would crack along the cuts, these being the weakest points? This is what's done with big slabs of concrete, so why not small domes of castable?

[robertjusher]

I have been planning on a 1 piece cast over sand oven using home brew mortar and stainless steel needles .
Seems to not be the norm but easyly the cheapest way to go. Fire clay is cheap, sand lime and cement is also cheap.
There are a few threads about it but not a lot.
I had not though of the cuts to give the craks somewhere to go, interesting idea.
I was thinking of long slow drying. Many small fire slowly getting bigger and then deal with any cracks with a top coat if required.
Does anyone know if normal builders cement is the same as portland cement?
I have never seen portland but it seems to be listed when people talk about homebrew.
Be interested to hear if any one else has gone down this road
ROb

[aiannar974]

The weight of the casting was stopping me from a one pc cast. Not sure how to move it. Do you think you can cast right on the firebrick floor? Maybe put down newspaper as a seperator.

Any thoughts?

Anthony

[david s]

Portland cement is calcium silicate cement. Both Builders cement and GP cement are Portland cement. Builders cement. Has more fly ash in it to assist it in being more fluid when making concrete.
Cutting the cast partially might work ok, try it and report back.

[robertjusher]

Thanks for the cement info David.
I plan on casting mine in place on the firebrick floor... I was going to use hebel as an under floor insulator. I read somewhere and agree that a low first couse of fb will give you a hard edge to stop your peel chipping the sides of the oven and set the thickness for the hand formed casting to sit on. The dome and enterence in 1 piece is the current plan.
A sand mould formed up on the floor covered in wet newspaper should be all the form I need.


This sand scooped out after a day or so should leave me with a nice enough dome.
I need to make my mind up soon as the top was poured yesterday,,,,

[david s]

Proprietary castables contain either natural fibres or polypropylene fibres which burn out at low temp and therefore leave minute pipes through which water can escape. This prevents or reduces the incidence of "blowing" where the steam pressure build up can create damage. As these will not be present in your home brew castable you should try adding something. You can get the fine polypropylene fibres, which melt at 160 C, from a concrete engineering supplies place or failing that use human or animal hair.

[doctorphreak]

wondering how big of a cast can a person do like maybe a 30-42" possible of will that be too big......also david approx how much hair would be needed to incorporate into the mix ???