42 build in queensland

[SirClutzz]

Front entry bricks now. I've installed a thermal break between the dome and the entry, with a 1cm gap, with a couple of lengths of ceramic rope between. The rope should ensure there isno movement between. I reused the inner arch form here, adding some spacers on the end to keep it centred. This helped me keep the arch curve the same, although the outer arch is 1cm or so higher then the inner. I'll be running a ceramic rope over the top of the inner arch for the thermal gap, so the extra height is accounted for.
Also completed the dome course that lines up with the inner arch, once again, it's tied in really well, so super happy with that part.

[SirClutzz]

Outer arch mortared in, the mortar gaps are super even, and it's really straight, so really happy with that. This arch was a bit easier then the inner arch, as these bricks are not as big/heavy. Also super happy that each arch brick here is roughly the same size (couple mm difference, I cut them in pairs and the centre brick ended up being nearly the same, so these range from 58 to 61 mm at the bottom of the arch.

[SirClutzz]

Outer arch formwork removed, still needs a bit of pointing, but pretty happy.
And the first full course of brick. The 360 degree lazer really helps avoid the drop here. I was a little unhappy with the back side of the arch bricks here for this course to sit on, mortar gap ended up a bit bigger then I had hoped, but it won't ever been seen, it's just my ocd kicking in. 2 small gaps will be plugged later when I get around to it.

[SirClutzz]

7th course was the first one where bricks started sliding off, so had to start using some wood supports at either end of the course. Also pic of the 8th and 9th course
The 9th course I started cutting the full size brincks into 3's rather then 2's. I also tended to cut 2 peices the same size, and 1 slightly smaller. I found this gave me options to avoid mortar gaps lining up between courses, although it did make it a bit of a jigsaw puzzle. Pretty happy with the result

[SirClutzz]

10th course was really tight for space, no longer able to look into the oven from above, which meant clean up time was a bit more difficult. One thing I found super satisfying for the last 3 or 4 courses by placing the last brick in the course. Due to tapering the avoid the inverted v issue, I could drop the brick in with the it tool from above, by had to tap it into the gap from the outer edge of the dome. Loved how structural it all felt at that stage.
Also another tip for this late stage, I tried to cut a consistant brick taper for each course, but at this stage that was becoming very difficult. In the end, cutting a few of the same taper, and then custom cutting the brick between was much easier. You can see from the below shot that I ended up with a consistant sized brick, then a few custom, then back to consistant, etc, etc. I would morter the fixed size one, then put another fixed size one on the IT, place it with a gap and pencil mark the fill brick before custom cutting. It was slow, but I'm happy with the result.

[SirClutzz]

For the final course, the key stone. I did consider another course, then a tiny keystone, but I figure the top of the oven would be more mortar then brick doing that, and didn't think it was worth the effort, so I decided to use 3 bricks to form the keystone.

[SirClutzz]

At this stage, I starting working on the flue gallery. Taking insiparation from other ovens out there and a commonly used kit oven, we had decided early on we were going to cast a flue gallery out of refactory castable. My wife wanted me to get that kit, cause she liked the look, but I wanted to actually make my oven from scratch, so this is the comprimise. We decided to create a template plug, then make a plaster mold of that plug, then finally pour the castable into the mold.

First up, made a cardboard template to get the look right, then I had some styrofoam blocks laying around for the basic shape. Used liquid nails to put these together, and cut out the hole for the flue to sit in. The hole it larger then the flue diameter, we will stuff the gap with ceramic rope, so there is a bit of give and hopefully nothing cracks. Then covered the whole think with expanding foam. This made the plug much easier to carve into a nice shape, and is much less messy to carve then the styrofoam

[SirClutzz]

started with carving the front, back, and top to get squared off side to work from, then using the cardboard template, carved down the curve. This turned out really good, just need to fill the voids in the foam now and make the mold box and mold from this.

[SirClutzz]

Built this box out for some scrap to make the mold in. We are going to mix plaster and pour that around the plug. Made the round plug for the flue out of extra white board, and an old plastic pot. This give a lip for the flue to sit on so it can't fall through.
We then covered the whole thing in clay to smooth out the voids in the plug, and get a nice finish ready for plaster.
Finally we poured the plaster, needs a little bit of patching around the cold joints in the plaster pour. I had never done plaster before so was harder then I expected. A tip is, move fast, once it starts to set, it goes off super quick.
Unfortunately, we couldn't get the plug out without destroying it.

[david s]

That's a lot of trouble to go to if you are just making one casting.
Here's a simpler method if you ever need to do another.

https://community.fornobravo.com/for...723#post435723

[SirClutzz]

Thanks David, that would probably have been simpler. Any tips for castable, I've never used it before, and the bags have come with no instructions, so I am assuming it's pretty much the same as concreate at this stage. I looked to get stainless steel reinforcement "needles", but I could only buy them in 10kg lots. To get around that, I grabbed some stainless steel cable, and unravelled the threads, as I was unable to find wire thin enough. So hoping that works, as much as the refactory guy said it's probably overkill anyway. Going to put about 1 or 2 handfuls of those in the mix.
I'm also trying to decide it I mix it by hand, or in the mixer, read somewhere that a mixer is not good for the castable.
As once cast, how long before I should take it out of the form, and then keep it damp/wrapped in plastic to cure.

[david s]

There are a number of things to do
1. Mix by hand in a barrow, not a mixer. That way you can inspect the mix and feel the texture whilst mixing.
2. Use chilled water because it’s very temperature dependent and will go off way too fast in our summer if you don’t. Do not mix more than half a bag at a time for the same reason.Do a little practice by placing sand in the mould, take it out again and measure its volume, so you know how much castable to mix up. Put any castable left over in a sealed container or it will goff and spoil.
3. Fibres probably are overkill, I use them because my gallery is quite thin. You could use AR glass fibres or basalt fibres which are ok for the temperature service range. If you make the casting at least 25mm thick you shouldn’t need fibre reinforcing. Check to make sure the castable contains burnout fibres (most do), by sieving a small amount. If not you run a bigger risk of steam spalling. Some very fine polypropylene fibres can be added for this if required.
4. Calcium silicate achieves full strength really early, in 24-48 hrs, so damp curing for two days is quite sufficient.
5. Make sure you use a release agent on your mould or you won’t be able to remould the casting without breaking the mould.
6. Wash barrow, mixing and placing tools thoroughly before making up the mix as even the smallest traces of Portland cement or lime work as powerful accelerants
7. Post your results.

[SirClutzz]

Would bees wax work as a release agent? I found a vid online somewhere that it would work, but it was not talking about castable (I think it was concrete). I'm not worried about breaking the mold to demold anyway, but would be nice to get a cleanish release.

Thanks heaps for the other tips. You clarified a few things, Any concerns about cold joints with the castable if I am mixing it in such small amounts, I assumed I would need to mix the whole lot in one go to avoid that?

Do you see any issue with using the stainless stell fibres I'm prepped already, I've got about a handful ready to any way.

[david s]

Would bees wax work as a release agent? I found a vid online somewhere that it would work, but it was not talking about castable (I think it was concrete). I'm not worried about breaking the mold to demold anyway, but would be nice to get a cleanish release.

Thanks heaps for the other tips. You clarified a few things, Any concerns about cold joints with the castable if I am mixing it in such small amounts, I assumed I would need to mix the whole lot in one go to avoid that?

Do you see any issue with using the stainless stell fibres I'm prepped already, I've got about a handful ready to any way.

Not sure about beeswax, I use a 50/50 mix of kerosene and motor oil. You don't want too much or it will adhere to the castingcreataing more work to clean it off if needed. Otherwise it will just burn away anyhow.
I don't know how thick your stainless wires are, but the stainless melt extract fibres which are the recommended reinforcing are 0.5mm thick.

So long as you apply the second mix straight away, there's no issue in it not bonding properly. I layer different mixes all the time and have no problems. Leave it for a few hours and yes it may delaminate once under stress. If you estimate your volumes correctly you should not end up too short and a small quantity to mix up and finish is pretty easy and quick. If you've overestimated a bit then you won't have too much wastage.

[SirClutzz]

Thanks David, the wires are around 0.3mm. I looked at one of the manufacturers in Australia (antec or something like that), and at the specs of theirs when trying to work out what size wire to get. The only way I could get near the size was the cable option.

Thanks for the tip on filling the mould with sand, I had thought previously about filling it with water, but I knew that would just leak and be no help, can't believe I didn't think of the pile of sand I have laying here spare... I used under 27litres of sand filling the mould, and I have 3 bags of castable. The seller told me it takes 4 to 5 bags to to a 1m by 1m by 50mm slab, so that works out to be 10 litres per bag, so I have 30 litres of castable to play with.

Does the motor oil/kero mix stain the castable, or more to the point, would it affect painting it afterwards. I'm guessing I'd have to use a strong detergent to clean that off once the castable has cured enough, or does it not really leave any residue on the castable.