30" Cast Scotland

[sergetania]

Dave, the dome looks great to me!
Personally, I like surprises... but only if I don't have to leave home!

[Mullster]

Cheers david s I'll have time to mix a batch for voids tomorrow or do you think that would be too soon to remove form and sand? It would have been 48hours since casting tomorrow afternoon. My wife just laughed when she heard the reason why I wasn't that excited about a surprise going away for 6 days, all I could think about was leaving the oven at such an important part of her life

Her life - I love it!!!

[Daveholdn]

Cheers david s I'll have time to mix a batch for voids tomorrow or do you think that would be too soon to remove form and sand? It would have been 48hours since casting tomorrow afternoon. My wife just laughed when she heard the reason why I wasn't that excited about a surprise going away for 6 days, all I could think about was leaving the oven at such an important part of her life

[david s]

The voids need to be filled before the cast dries too much so it’s probably better to leave it as is until you return.

[Daveholdn]

Haha cheers Mullster , aye was getting excited as I was casting, could taste the pizza
Thanks david s, I'm gonna have to remove everythingtomorrow as we are off on a last minute 6 day holiday on Friday. I currently have a tarpaulin over the top of the oven and there is condensation, should I remove this and let it dry naturally as the hot weather seems to have passed, our one day of summer up here has gone

[Mullster]

Looking good - that dome looks really smooth! Just wait til you hollow out the sand - proper starts to feel like an oven!

[david s]

That looks ok to me. Sudden corners tend to be weak points and a more funnelled flue gallery would have addressed this as well as perform better, but I think you'll be fine. Allow a couple of days before remoulding, then remove the sand, inspect the inside and fill any voids with the homebrew mix (you can sieve out the larger grains of sand for this) then damp cure the casting for a week.

[Daveholdn]

So I cast today, was a lot hotter than I thought it was going to be so completed it in 5 batches! Mixed by hand as my mixer never came through so thanks david s for the heads up of consistency required. I weighed the dry mix of each batch and worked out 2.5% for the ss needles required for those about to cast.

Overall happy, the homebrew was nice to work with, better than the sandcastle, but think I've got carried away with the flue, I think I've gone too high and no idea why I made it square when it's cast round a circular 150mm diameter object, I'll put that down to "lost in the moment"!! I also forgot to put the tapered sides on the flue, totally forgot, will this be a problem in anyones experience? And will the height of the flue I've cast be a problem or can I cut once cured?

Thanks again for the help.

[Nick J C]

I did mine in two mixes, although it wasn’t too hot a day. Lasted a lot longer than the render mixes, which needs to be sloppier

[david s]

No it needs to be stiffer than mortar. Use "ball up" consistency, ie make a ball about the size of a cricket ball toss it 2 ft in the air, you should be able to catch it intact.If the mix is too dry you will get too many voids, if too wet it won't stand up vertically and will shrink more.

[Daveholdn]

Apologies wasn't online for a while there but thanks Mullster , your pics helped everyone mate, but you salvaged it back well. Loving the black arch.
Thanks david s, aye your defo right, unfortunately I've already set up my mould and gallery ready for casting, and with 2 wee kids running around I've only a small window to get the cast done starting this afternoon.

With that homebrew casting, is it the same kind of consistency you're looking for when mixing mortar? As in sticks to the trowel when you turn it upside down? And I'm going to work in batches here, but what experience have people had with an acceptable amount to pre mix before it's starts to get unworkable?

Cheers.

[david s]

Yes, that’s the reason I keep suggesting that you should cast the oven first, remove the oven mouth mould plate then place the flue gallery mould against the dome cast and then cast the gallery. It is normal to create a “release” when designing a mould. That is to make it slightly tapered to allow for it easy removal. Definitely place some wedges under it so it can drop after it’s cast. Do not force the mould out or you can crack your casting. If it won’t remove easily attack it from the inside with an angle grinder and remove the pieces carefully. Polystyrene is a better material than MDF for this mould as it is easier to remove without damaging the casting.

[Mullster]

Daveholdn It’s looking good - just make sure you have figured out how you will remove once you have the frame piece for the flue vent too - that was a particularly tricky part for me and definitely lead to problems getting the frame out because of the way I engineered it.

i think the use of shims to ‘lift the frame’ a little helps but isn’t the full answer

[Daveholdn]

Flue gallery form is almost complete, I used mdf and hardboard but will ensure they are well sealed so the water doesn't get in and swell the boards. I've still to put the funnel for the flue on, but with regard to dimensions, is there any best practise here or is it just a case of ensuring the funnel is big enough to fit the 150mm diameter flue on? (using the good old delux paint tin as seen by other builds) Also, if there are any experts on the gallery, I'm a little concerned my oven mouth depth is a little short, it's currently just over 60mm before leading into a 1/2inch lip for the door. Will this depth be a problem with smoke or should be OK?

Cheers

[Daveholdn]

Haha cheers Mullster, I think I'll leave the grinder for now, try and level them using dry fireclay and then see how it is. Did you find the sand from the mould filled in the small gaps between some of the bricks? I was gonna try and brush some of the mould sand into the cracks but unsure if normal sharp sand isn't the best for the this? Did read the somewhere, Ash from the subsequent fires is great at that and provides some kind of natural insulation?

I'm gonna try and mould the sand this weekdn and cast. It's getting real

Cheers