New 36inch castable build in Brisbane

[david s]

Re: New 36inch castable build in Brisbane

The preferred method of reinforcing castable is stainless steel needles.Stainless so they don't rust and needles so the heat dissipates easily to the surrounding refractory. Using thicker reinforcing is problematic because as heat is applied it goes to the much more thermally conductive material which then gets hotter and therefore expands more than the surrounding refractory. The needles make placement by hand more tricky. I often get stuck by one or two. You learn to handle the stuff with care.

[vanoontour]

Re: New 36inch castable build in Brisbane

Have you put any form of reinforcing in or would the thermal difference cause issues?

[david s]

Re: New 36inch castable build in Brisbane

Calcium aluminate cement does not need extended curing like Portland cement. 24 hrs is all that is required. I always cover it after placement, but it can be removed from the mould, or the mould removed from the casting, in your case, the next day.

[david s]

Re: New 36inch castable build in Brisbane

Well done. Using the same method you can now pile some more sand in front of the door to create the formwork for the flue gallery. Remove the door formwork first, and remember to create a rebate so you can fit an oven door against the opening. The flue gallery casting therefore needs to be both wider and slightly taller than the oven opening.After you've finished that you can remove all the sand.

[brissie]

Re: New 36inch castable build in Brisbane

Thanks for the advice David s. I did have enough castable for 80mm walls. I was not sure how far it would go. 10 x 20 kg bags is about right. It was funny to work with. I bit spongy but did do the vertical start okay. I also went with your suggestion, to just use the sand mould. I did attempt a form work solution based on conical sections for the start of the dome, but found I could not bend the thin ply I was using. I could hove cut slits in the outer layers of the ply to allow it to bend, but your simple solution worked well.

I used a central spindle to make the sand dome, photos attached (thanks Golf for the idea) . I coved the sand with wet newspaper, and sprayed with can of vegetable oil to help with it, and the timber partitions removal. I divided the dome into 4 pieces for easy of moving to the final position and to allow for moment/cracking.

In the end I did not use the second stage scraper, as the dividers worked well, and gave a depth gage to work from. I poured the castable in the late afternoon as it was a hot day (mid 30's c), and used ice in the water to reduce fast setting issues.

[david s]

Re: New 36inch castable build in Brisbane

You can always clad the 50mm wall thickness in concrete using fine aggregate (7 mm blue metal) and 50/50 lime and cement. Use 6:4:1:1 aggregate,sand,lime cement. This is a cheaper way of making the walls a bit thicker. Work up to a stiff mix and apply by hand. It will stand up by itself vertically if applied by hand to a thickness of around an inch and a half. The lime kills the skin on your hands though, wear gloves or a barrier cream. You can also do the dome with the castable mix in this way without having an outside mould. Just start at the bottom and work your way around. The stuff goes off so fast that working in small batches will stiffen up pretty quickly to support your next lot as you rise up the dome sides. Wriggle the stuff against the mould to avoid getting voids.

[brissie]

Re: New 36inch castable build in Brisbane

The image is an overview of the oven. I may cast it over the weekend.
It is conceptual. Originally I created 80 mm walls now 50mm . Castable is expensive, so the reality is that the walls will be 50+ mm thick. The image shows to scale to the 80mm design. With some alterations at a 50mm thickness.

Domes are hard to do with slumping concrete. so will form a conical section on the start of the dome with form work, and build remaining dome on the lower layer support.

[david s]

Re: New 36inch castable build in Brisbane

a layer of glass bats between the two boards, with a few cut hebel blocks under the load points.

built this way the glass bats won't compress. I used a similar, system to insulate under the floor of my first oven. It worked pretty well.

[brickie in oz]

Re: New 36inch castable build in Brisbane

and place a layer of glass bats between the two boards,

Once its compressed its useless.

[oasiscdm]

Re: New 36inch castable build in Brisbane

Looks good Brissie.

[brissie]

Re: New 36inch castable build in Brisbane

Added the top two Hebel boards last night.

Ran out of liquid nails, 3 tubes. the rough texture sucks up adhesive. The structure should be sound though. No side movement, and with an oven on top I don't think it will go anywhere. I did pay attention to the layering detail, placing the steel under the load points. the dome walls will be sitting over the walls or steel sections. First time I have worked with Hebel. Checking the product specifications is difficult.

It looks like its R value is about 0.7, so two boards will be effective in keeping some heat in. If I started again I would drop the steel and internal block wall down a bit, and place a layer of glass bats between the two boards, with a few cut hebel blocks under the load points. That would be very effective insulation. Construction strength would be much the same.

[david s]

Re: New 36inch castable build in Brisbane

Disagree David.. the Hebel adhesive is meant to work with the product, creating a monolithic bond. I found applied correctly I had working time. The laid nails will work but does not provide a solid mass of that it's the right terminology.

In brissie application it will work but I would have used the adhesive. I didn't find out sucking the moisture out at least not like the fire bricks did.

I even tested it on some blocks scraps, then break them a week later and it broke not along the bond. Enough proof of hebel claim.

Anyhow, looking good brissie. Keep photos coming.

Actually Colin I think you are right. Now when I thought about it more, I think it was a normal mortar that I had trouble with in conjunction with the Hebel. I have used the Hebel adhesive though. It was at least 6 years ago. (getting old)

[oasiscdm]

Re: New 36inch castable build in Brisbane

Disagree David.. the Hebel adhesive is meant to work with the product, creating a monolithic bond. I found applied correctly I had working time. The laid nails will work but does not provide a solid mass of that it's the right terminology.

In brissie application it will work but I would have used the adhesive. I didn't find out sucking the moisture out at least not like the fire bricks did.

I even tested it on some blocks scraps, then break them a week later and it broke not along the bond. Enough proof of hebel claim.

Anyhow, looking good brissie. Keep photos coming.

[david s]

Re: New 36inch castable build in Brisbane

Your supporting column in the middle should be sufficient. The other joists have me a little worried. They look like pine, but if they're steel, ok. You could also easily cantilever the Hebel slabs about 100mm or so over the outside of the stand if you want more room. There's not much weight in the outside of the oven..
If you are keen to use the liquid nails get Liquid Nails Landscape. it is designed for masonry and is incredibly strong. I would use it in preference to the Hebel glue, that stuff is difficult to apply because the Hebel sucks the water from it in an instant.(sorry Colin)

[cobblerdave]

Re: New 36inch castable build in Brisbane

I agree, it's not cheap though. About 1/3 weight of standard concrete so probably about 1/3 strength too. 6 mm reo cast into it is rather inadequate IMO. Two layers should be plenty. I used 75mm Hebel power panel for my mobile oven as both structural and insulating layer, apart from the 1" vermiculite between the floor and the Hebel, in an effort to save weight. I am a bit disappointed as it's proved inadequate regarding strength. It has cracked quite badly although it doesn't really matter as it's contained in a steel cradle. Not sure whether the cracks have occurred because of heat or going over rough roads and speed bumps. Suggest if you are using Hebel to have support under the middle of it as well as the sides.

Gudday
I agree with Davids . I would go with some joists even though Hebel claim is that hebel can span up to 5 mtres with no joists. But with on oven sitting on it? An oven would weigh more than any piece of furniture . I couldn't pull up the tec spec without a login but I bet you couldn't put a piano on it.
Bunnings had hebel in there stores for a while and don't stock them now as I recon the public cracked and broke more than they sold. I like the stuff but you have to be gentle with it , it breaks so easy.
By the way I have it as insulation under my oven and made an insulated door of hebel so I'd do like the stuff.
Regards dave