Finally decided on 32in castable dome

[Mullster]

Materials have arrived!

Never been so happy to see a pallet of anything let alone bricks in my life!! What is this oven doing to me?

Cannot wait for the torrential rain to stop and the weekend to come so I can move onto the firebrick floor. I believe I have all the materials now for the next few stages - can’t wait. Already getting a bit apprehensive about the flue casting stage but I’m getting ahead of myself.

[Mullster]

Laying the floor

After being so excited to get started on the floor I had a nervous and slightly overwhelmed feeling when I got started today. I realised I had chosen the width of my landing based on the size of the oven opening rather than using a ‘multiple of a brick width. After a bit of deliberation decided to go for six bricks wide which slightly overhung my vermicrete layer which I was a bit concerned about. I didn’t need to be though - I found a solution later on.

As I’ve seen many others do I laid the brick pattern a couple of times to check everything before making my first cut. I used a bolster for some but decided I wanted more precision because a couple did not break off very cleanly. Using the diamond blade on the grinder and dunking the bricks in a bucket of water to try and reduce dust I found the cutting pretty easy.

I scooped up all the brick dust and mixed with some sand and spread on top of my insulation layer before starting to lay the bricks. If I had my time again I would have used a bit more sand mixture to make the laying a bit easier.

I’m sure other first timers have done better. The floor is not perfectly level but on the other hand I’m not sure any of the ‘lips’ are significant enough to catch a peel on.

The last thing I did was cut away the excess vermicrete having used a square mound. Hacked away with a bolster before trying a hand saw. Worked a treat! Especially good as it was 2130 - don’t think the neighbors would have appreciated the grinder at that time!

I then used some of the vermicrete ‘dust’ to fill my small thermal break between the landing and the oven floor. You can see the slightly darkened line at the top of the stood up bricks.

Overall I’m pretty stoked. I think it’s good enough and I’m excited to get onto the dome soon!

[Nick J C]

Nice work.... particularly loving your choice of pencil and ruler

[Mullster]

Nice work.... particularly loving your choice of pencil and ruler

Particularly professional

[Mullster]

Creating the framework/mould

So I’ve decided to go for a one piece cast of the dome and flue gallery having seen Nick J C and his recent build.

The frame took me a good few hours today but I think I have a workable frame now. I managed to find wood lying around for everything. The plywood boards I had used for shuttering the hearth pour got chopped up and re-used.

Ive been conscious to make sure I can dismantle the frame from the outside front - assuming that it won’t simply slide out!

Design question - I’m planning to make a castable front - similar to david s and Nick J C . Right now the front edge of the bricks in the opening would be butting up against that castable front without any insulation in between - is that a problem? I did manage to create a few mm thermal break between those bricks on the dome floor bricks so hoping that they won’t get roasting hot anyway.

Im off work this week, so really hoping I can get casting over the next few days.

[Nick J C]

Hi Mullster.... I will leave the technical advice to David. Notice youve gone for a paint pot for the flue mould too - handy UK sizes - just over 6"! Mine got quite stuck and needed quite a bit of force to get it out, so consider wrapping in in clingfilm or something. I also stuck parcel tape all over my formwork which made the mould come away easily and the cast surface smooth - I also used clingfilm over the sandcastle, as the paper didnt stick down very well,and this seemed to work very well, with a nice surface to the inner dome, and no paper stuck to the dome. I also put the main formwork on to some 6mm battens, which slide out when cured, to allow formwork to drop away from the mould.

A couple of things i would mention re: your design - most casts are arch shaped rather than flat topped - I expect it will be fine, but the arch design is inherently better at taking load, and less likely (pretty impossible) to collapse. I would also suggest making the 'funnel' as big as possible (I enlarged mine) as this apparently improves the draw, and reduces smoke loss from the front.

[Mullster]

Hi Mullster.... I will leave the technical advice to David. Notice youve gone for a paint pot for the flue mould too - handy UK sizes - just over 6"! Mine got quite stuck and needed quite a bit of force to get it out, so consider wrapping in in clingfilm or something. I also stuck parcel tape all over my formwork which made the mould come away easily and the cast surface smooth - I also used clingfilm over the sandcastle, as the paper didnt stick down very well,and this seemed to work very well, with a nice surface to the inner dome, and no paper stuck to the dome. I also put the main formwork on to some 6mm battens, which slide out when cured, to allow formwork to drop away from the mould.

A couple of things i would mention re: your design - most casts are arch shaped rather than flat topped - I expect it will be fine, but the arch design is inherently better at taking load, and less likely (pretty impossible) to collapse. I would also suggest making the 'funnel' as big as possible (I enlarged mine) as this apparently improves the draw, and reduces smoke loss from the front.

Thanks Nick - good tips! I’m all in on the rectangular oven front now it’ll have to work! I really like the idea of the contrast of the straight line with the dome behind. I assume you did cling film on top of the wet newspaper rather than missing out the newspaper altogether?

[Mullster]

Building a ridiculously frustrating sandcastle

So today is easily the trickiest task so far for me. I’m not sure if I was doing it wrong but it took me hours to get the sand dome finished despite trying to load up with all sorts of bricks and tiles to take up space.

I started by making sure my inner dome outline was visible. Then made the 16” guide of a garden cane screwed into a flat piece of hardboard. Marked a large cross on the hardboard and the dome floor so I could line up the cane in the centre point.

Stacked up many bricks, rocks, bathroom tiles (cutoffs from the latest we are not going on holiday so we might as well spend money on the house ventures) And even a terra-cotta plant pot for good measure.

Still used up every last bit of sand I had bought for casting the dome. Had to go out and buy several more bags! Could be worth an edit to the calculator spreadsheet for the home brew because I don’t recall it accounting for the sandcastle.

Used a flat trowel (big rectangular one) which maybe wasn’t helping as much as a homemade curved one would have, but even still, found it incredibly frustrating to get the sand to do what I wanted it to! Experimented with spraying it with water, drenching it with water, making sand slurry (just sand and water) - I’m still none the wiser which was the best method

Anyway I have a dome. It’s definitely not perfect - but it’s good enough I think. It’s not more than 1/2 inch out anywhere according to the guide I made (wooden curved measure).

I’m feeling like the casting will be easier than that - I hope I’m not wrong!

[david s]

Ha ha. You obviously didn’t spend a great deal of time at the beach as a kid building sandcastles. I read somewhere that the ideal water content is 10%, but as sand usually already has a fair amount of moisture in it then it’s easier to go by guesswork.
Regarding the wet newspaper or cling wrap, you actually really don’t need either. It’s simply a way of making sure your casting doesn’t end up with a coating of sand on the inside. I prefer the wet newspaper rather than clingwrap because clingwrap can move easily creating uncovered spots and folds making creases which can get trapped in the casting.

[sergetania]

It might have been painful but it looks nice and clean. Please provide a detailed description of the casting process. Building a sand dome is reversible, casting the dome itself is not. I am intimidated.

Btw, has anyone tried to add something other than water to sand when building the sand castle to make it stickier?

[Mullster]

Casting day - it finally feels like an oven!

So I’ve managed to cast today. Found this so much easier than the sandcastle .

Used they tried and tested home brew (sand, lime, fire clay, cement) with the poly fibers (Bostik) added but without SS needles as they were hard to find and a couple of threads suggested they are not a necessity.

Mixed the ingredients dry using a 2 liter jug To measure out into a flexitub. Used a small trowel for the first few batches before realising hands (with gloves of course) was much easier and quicker. Didn’t have a measure on the water - it was approximately 3.5 of a random sized tin - sorry that doesn’t help anyone!

A very hot day here so the paper kept drying out had to keep wetting it. The mix went on really well. Kept using a tape measure to check it was 2” (or just over). Took me a lot of batches and probably 6 hours solid work. Used a trowel to put it on and similar to a bricklaying technique notched it as I lay it and then smoothed from the side.

As for the paint tin I waited for the cast to start forming and then rotated it carefully about an inch 2 or 3 times through the day hoping it makes it easier to remove.

I can’t remember exactly what I do next but I think I have to keep it damp? Do people use anything particular to achieve that? Plastic cover?

I know there is still a way to go but I’m feeling like I’m almost there.

[Nick J C]

Great progress..... I wrapped mine up in shrink wrap, and it was covered in a reassuring amount of condensation by the next day.....I suspect you will need something other than an intermittent wetting in this heat wave

[david s]

It might have been painful but it looks nice and clean. Please provide a detailed description of the casting process. Building a sand dome is reversible, casting the dome itself is not. I am intimidated.

Btw, has anyone tried to add something other than water to sand when building the sand castle to make it stickier?

Sorry it’s probably too late now, but you can add a little powdered clay to it which makes it stickier. Other things that would work are PVA or plaster of Paris.
I’m pretty sure those sculptors who do amazing beach sand sculptures just use sand and water.

[sergetania]

David, like dust from cutting firebricks? How little? Is there a danger of adding too much so it becomes too hard to remove? Thank you!

[Hattori-Hanzo]

Looking good Mullster

I'm at pretty much the same stage as you at the moment. Just waiting for the dome to cure for a few days before removing sand.
The home brew works surprisingly well, its easy to shape and holds well.

I've just covered mine in a heavy tarpaulin and gave the dome a good spray of water before covering up. If the newspaper was nice and wet this should help to retain some moisture in the dome too.

good luck with the rest of the build and keep us posted. not sure why your photos are being rotated 90 degrees though?