Finally decided on 32in castable dome

[Nick J C]

Hi mullster, I have done mine pretty much at the limit of what is reasonable.... 2 weeks cure time for dome. I dug out the dome after 48 hrs and added blanket and Vermicrete on day 5. I started curing fires at 2 weeks, and am now 4 days into curing fires with significant heat and nothing untoward happening so far. If you want to be sure to maximise dome strength, it will need moisture, therefore the longer you leave it wet the better....no reason not to put the blanket and Vermicrete on though

[Mullster]

Looking for some advice (as usual). I might be able to ‘cast’ my decorative arch this weekend. Am I right in thinking I need a product like ‘Ronseal Concrete Seal’ to make it shiny and look polished?

[david s]

Yes, assuming you polish it first.

[Mullster]

Nick J C did you say you used more than 100l of vermiculite on the dome insulation? I might get to that stage this coming weekend but only have maybe 95l on hand - wondering whether to order another bag.

Happy to hear anyone’s else’s experience too

[Nick J C]

I used over one bag....nearer 2 (I used 1 bag vermic, one bag perlite for no particular reason). Good luck. N

[Mullster]

Flue choices - advice please

So after several hours researching this forum and elsewhere online I’m still not sure what to go for flue-wise.

I know it’s 6in diameter, I know I like the look of black rather than steel, I know I need a cowl to keep out the rain etc (currently lashing it down - it is British summer time after all).

As I’ve built my oven next to our existing deck, my plan is to make a covered pergola across both, likely with either glass or polycarbonate sheets as the roof material, however I’m also considering other materials for the section of the roof that will cover the oven (there needs to be light getting to the deck area when it stops raining ).

None of the pergola is built, so right now I’m planning a 1000mm flue that will take me ‘through’ the roof when it’s built.

So my questions are:

1. Is this is viable concept (flue extending through a pergola roof)
2. Assuming yes, does it make any significant difference whether I go single or twin walled for the flue?

There is little risk of people burning themselves by touching the flue. I’ve read that the twin walled ones still get hot anyway. I’m not sure how much if at all I need to be concerned about the heat approx 900mm up my flue that may be close to the pergola roofing?.....

Another decision I’d appreciate views on please guys.

[aaronpizza]

Mullster thank you for posting your mistakes!

I will certainly learn from them!

Sadly I've been totally stalled due to too much work/laying a new patio and the good old British weather!

A double skin flue will have better draw, so this might be better - or will it suck out too much head? IDK you need a oven pro for this!
A single skin flue will get very hot I'm sure, if you have any concerns about burning, I would want to avoid this.

If there is anything near your flue, it may/will get covered in black soot, so if this is going to be below your glass roof, this may be a problem, also this may then trap the smoke etc under the roof, in your face?

You could be super snazzy (I'm thinking about doing this btw), get a hole cut in the glass and put the flu through it (don't let the flu touch it) and then the risk of smoke will be gone.
The length might be too long then though? IDK

It looks good btw!

[Shaunster]

1. Is this is viable concept (flue extending through a pergola roof)
2. Assuming yes, does it make any significant difference whether I go single or twin walled for the flue?

Yes its viable, but not single walled. Certainly you want double walled and extend it further above the pergola roof, you just have a hole in the roof and flash as with any other pipe/vent that goes through a roof. Twin walled flues do get warm, but not hot like single walled.

[Mullster]

Yes its viable, but not single walled. Certainly you want double walled and extend it further above the pergola roof, you just have a hole in the roof and flash as with any other pipe/vent that goes through a roof. Twin walled flues do get warm, but not hot like single walled.

Thanks guys - I think I will go twin walled to be safe and yes the plan is to cut a hole in the roof of the pergola (that doesn’t exist yet) for the pope to pop through.

[Mullster]

Aaaarrggghhhh!! A twin wall will not fit in the hole I’ve cast!!! (Unless I manage to find a 4inch internal, 6inch external) pipe!!!

Plan B - investigating if I could do a single wall 6inch for the first 500mm from the oven and then join a twin walled onto that for the top section that will go through the pergola roof....

[david s]

Yes you can do that. I’ve done that with two oven installs that go through a roof. You only need the double bit where the flue goes through the roof, so it also saves a bit of money. You can also use a standard colourblind sheet rather than stainless for the outer flue pipe. Any sheetmetal shop will make it to whatever diameter and length you require.

[Nick J C]

I don't have a double walled one either, mainly because it would have been 8" thick which would have looked oversized and increased the gallery size required....as David says, it only needs insulating at the roof penetration.....I will probably wrap mine with some glass fibre stove tape at this point..

[Mullster]

Casting my oven front

After my previous framing mistakes for the gallery I took particular care today to try and get the frame right for the front.

I made use of a premium piece of kitchen worktop in the hope it would give a nice smooth finish! I’d been saving it for nothing in particular so why not?

I then used mosaic tiles leftover from a recent bathroom renovation before making up a batch of concrete with pea gravel as the aggregate and a cement pigment called bond it. Hoping it comes out black which I think will look good if the mosaics have set well. We’ll see!

I also made 6 hooks/rings out of stripped electrical wire and embedded into the cast so that I can tie it to the dome.

All covered over with plastic now to cure slowly - but how long do people think I should give it before taking the frame off? Obviously it’s a fairly small amount compared with a slab or something so are we talking a few days or week or so?

I really have my fingers crossed!

[Mullster]

It turned out good!!

So I waited 5-6 days before removing the frame for the oven front - I thought it would be good for it to dry out a bit more before polishing.

Invested in a set of concrete polishing pads for the angle grinder (cost has gone out of the window by this point ). Watched myself a YouTube video because it’s my first time polishing concrete.

Kept it wet throughout. Not a quick process. At times I could barely hold the grinder my hands had gone so numb/tingly!!

But I’m really chuffed with the result. I was worried the mosaics wouldn’t show, or the concrete dye would be too pale but overall I like the look.

Just hope I can be successful in applying the blanket, vermicrete and fixing the flue and front in place tomorrow - a big day!

[Nick J C]

That’s a funky arch!