30" Cast Scotland

[Daveholdn]

Hi Team,

I'm moving my posts from the Getting Started forum, under 30" cast pizza oven - Scotland so I can get a little more input here. I've used a lot of resources available on this forum and it has helped no end, so thanks.

I'm basically building a 30" internal diameter pizza oven using home-brew, sat on vermiculite, CF board and Firebricks. It will be insulated with 50mm home-brew, 50mm superwool, 25mm vermiculite layer and then a render.

I plan to cast the gallery all as one with a small heat break, angles cut out of the bottom of the entrance firebricks and stuffed with either left over CF board or vermiculite, seen from previous builds

I've built my base and added the 50mm vermiculite slab, the weather then turned in glorious Scotland style and basically smashed it down for 2 weeks which stalled me a little. The weather is now a little better so I've now managed to cut the CF board to shape and then measure and cut the firebrick floor, probably the hardest part for me as i'm not really DIY orientated!!! but I'm sort of happy with it. All photos attached.

There are a few lips on the floor which are annoying me, I'm just wondering what people have used when levelling the floor. reading the resources I think using a mix of dry fire clay and sand would work? Is it just normal sharp builders sand I can mix? And I take it you just scatter on dry where it is required.

Also I have had to cut my CF board into 3 sections, I've ordered CF silicon strips to join them together, in anyones experience is this the best way or can you just push them into place and hope the firebrick floor keeps it in place?

Cheers for your help.

[sergetania]

Hi Dave,

That is a good start, looks very nice! I have started a 30" build as well.

I have been wondering about leveling the cooking surface too. What if we go at it with a grinding masonry wheel to make it smooth? Making the bricks the same size instead of trying to use sand to make the base uneven to make up for brick size differences? Just a thought, someone with more experience will hopefully help.

Best of luck with the build!
Sergei

[Daveholdn]

Hi sergetania , thanks, not a DIY person as such but loving this. I'll have a look at your thread. I've rwad somewhere that it's OK taking a lip or 2 down with the grinder, but I've quite a few, I think the bricks where from about 12 different batches, but think I'll try today with a bit of fireclay or just sharp sand to level, I'll let you know how it goes. Are you using cf board under the bricks? If so have you had to join them together at all? Good luck to you as well mate, cheers.

Dave

[sergetania]

Dave,

I am not that far into the build yet. Just finished a stand and getting ready to cast a concrete countertop.
Planning to use a cf board and just going to lay it down, multiple pieces, nothing to join. My understanding is the weight of everything else on top will hold it down. Hope someone will correct me if I am wrong.

[Mullster]

Daveholdn great to see your thread started - been wondering when you would .

Looking great so far too.

I had some similar ‘lips’ when I first laid my bricks but more because I was laying onto the vermicrete layer directly rather than differences in the bricks. At the time my fireclay hadn’t arrived but I did have a lot of dust from the brick cutting so I simply mixed that with some builders sand to do the leveling. Definitely nothing scientific in my case - I simply scattered it and then as I lay each brick I put more or less under the next one to level it off.

It didn’t end up perfect but it was as good as I could. Since then I’ve cast the dome and emptied it of sand. I even tried using a peel in the oven - no catches whatsoever despite what I thought where some leftover ‘lips’.

From my perspective I’m glad I didn’t set about trying to grind things down or anything - it would have been unnecessary as it turns out for me.

[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

[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

[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

[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.

[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]

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.

[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

[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.

[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.

[Mullster]

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