Cast Dome Build Brisbane

[Reidy]

Hi All,

Just getting into the build of my new WFO and thought i'd share progress. Going to be a cast dome construction with a 900mm internal floor dimension with 450mm entrance width.

I just picked up most of the materials last weekend including 75mm fire bricks for the floor and Refractech Castable for the dome. Also picked up 50mm ceramic fibre board for under the floor and 50mm blanket for the dome. I managed to find a guy in Brisbane who is selling all of the refractory materials so got it all from one place and at a pretty good price i think.

So far i have almost finished welding up the stand and cut the board for under the bricks. A few pics below show where i am up to. Hopefully finish the stand this weekend and starting cutting the floor bricks.

Any feedback would be great.

Cheers
Reidy

[UtahBeehiver]

David S is our resident casting expert and he is just up the road from you (well kind of in Townsville, Queensland).Look at his posts and thread. He does cast ovens commercially and has tons of tips. He can confirm yeah or nay on the refractory cast, I do know he says to make sure the product in a dense cast not an insulating cast.

[david s]

I can’t see how thick the steel is, but ovens are really heavy and your stand appears to be no where strong enough. It needs to be stronger than you would think. Also if it is to be sitting in that deck you’ll need to weld on some horizontal pieces at the base so the weight is not sitting on those four legs. The deck supports may also need reinforcement to take the extra weight. A collapse can be catastrophic Also add some diagonals or at least gussets at the corners.

[Reidy]

Hi David,

The steel is 50x25x2.5m. I was planning a few braces and possibly doubling the legs and putting some plates on the bottom. The other thing I was sure was if the 6mm FC sheet was enough under the fibre board. The steel is about 200mm centres across the top. I estimated 6bags of castable and the floor is about 40 bricks, so the overall weight I think will be 400-500kg. I’ll post a better pic of the stand later as my iPad won’t let me add one.

It wont be living on the deck. Ill be making a spot just off one side which is propoerly supported. I was thinking of casters on the legs but not sure.

cheers
reidy

[Reidy]

Got chrome to work for the pic

I am also planning to have a steel band say 50x3 flat bar, welded around the circumference of the dome onto the ends of steel support rails.

[david s]

The normal base for an oven is 100 mm reinforced concrete. I think 6 mm cement sheet over 200 mm spaced steel supports is way too thin. Either 18 mm sheet or weld more bearers so they are 100 mm centres would be better.

[Reidy]

Thanks mate. I did think it was maybe pushing it. I was trying find some 12mm sheet but couldnt get my hands on any for a decent price. Anyway I went ahead today and whacked some more supports in. Space between supports is now 95mm. Also put in some bracing around the bottom. Didnt go with Doubling the legs yet, Might see how it goes. I can always add them later.

trimmed the entrance back. So it will be about 280mm deep and actually had to make it a bit narrower so its now 400mm. Hope thats not too narrow or too deep. The reason to go a bit narrow was to fit the bricks either side. See pics to see what I mean.

Also marked how I will cast the entrance with a rebate for the door. I will make up some timber forms for the front to give me the mould for the rebate.

cheers
Reidy

[Reidy]

Ok, stands done. Just needs a lick of paint. I think you can land a 747 on it now.

ready to cut some bricks.

[Reidy]

Finally got around to cutting the floor bricks. Almost done, just the front ones to go.

What’s the general consensus on having a heat break in the floor at the door? There seems to be mixed opinions( although most subjects do) I was thinking of cutting the bricks where I have the ply in which second photo but not sure if it’s really worth it’s. Possible a stainless steel square tube?

hopefully I will get the entry form done up tomorrow and then I’ll be ready to cast.

also meant to reply @Utah, yes I am pretty sure it dense castable. The weight on the data sheet indicates 2000kg per cube so it should be good.

cheers
Reidy

[rwiegand]

I don't have thermal breaks anywhere (and I haven't made a decent door yet either) and my oven is at ~325 (163 C) the second day after firing and will cook a pork shoulder perfectly. I don't need it any better than that. It's actually a little hot for bread on day two, one day after firing. If you're trying for 4-5 cooking days after firing it might make a difference. Three is good enough for me.

[Reidy]

Decided not to bother with the thermal break. Thanks for the info.

Ready to build a nice sand castle now.

I plan on adding some steel fibres to the castable but i only got my hands on enough to equate to around 1% by dome weight. My calcs have me around 140kg for the dome and i have around 1.5kg. Any thoughts on whether is this enough or is it worth getting more?

The last thing on my casting checklist is Polypropylene fibres. I dont have any at the moment and not sure where to get them. Are they too important not to use? Does it just mean slowing curing is recommended?

Cheers,
Reidy

[Reidy]

So made a fair bit of progress. Dome is done and entrance has been formed and cast. Slapped on the insulation blanket this afternoon ready for the first ceremonial fire tomorrow.

Turned out that the refractory already had the burnout fibres and I went with the needles I had.

the only query I had was about the thickness of insulation recommended around the entrance. Currently I have 25mm on the sides and top of the entrance arch but not sure whether I should double it to 50mm like the rest of the dome?

[david s]

It looks like you’ve run out of room to give the blanket a vermicrete layer. Are you planning on rendering directly onto the blanket? It can be done, but the surface is rather springy to work against. Perhaps do a few thin coats with 24 hrs between each. I like to wrap the whole oven in clingwrap for a week to hold moisture in the outer layer to enhance strength. Nice build by the way, you’ve done well.

[Reidy]

Hey david, yes the plan was to render straight over the blanket. In saying that there is no reason the final dome can’t extend past the steel work on the stand. It might almost be an advantage if it does extend out 10-20mm so water will not run behind the steel and into the insulation board underneath. I might consider doing a vermiculite later but how thick should that be to be effective?

Dome was cast about two weeks back and I kept it covered and had a wet towel on it for a few days. So should be pretty solid I think.

Its on its way now