Homebrew NE England. Help needed please.

[TonyPizza]

Nick J C If I plan to make a door for my oven (I am following the work of Nick J C very closely), will I achieve the same effect of putting the door further in 'past' the flue by putting the door at the gallery entrance and buying a pipe with a damper installed?... therefore sealing the unit. It's just that I am a little tight on space and I could do with making a shorter gallery, so I can keep to about 750mm internal oven size.

[Nick J C]

Doesn't seem to be the done thing....probably because you will lose heat rapidly via the flue whether you seal it with a damper or not....an issue for long term heat retention, limiting the utility of the oven....fine for pizza though

[TonyPizza]

Doesn't seem to be the done thing....probably because you will lose heat rapidly via the flue whether you seal it with a damper or not....an issue for long term heat retention, limiting the utility of the oven....fine for pizza though

Thanks again. I've got 1100mm square two work with, so I will probably aim for a 700mm internal diameter.

[TonyPizza]

Thanks again to everyone for the help this far.
Nick J C today, I’ve nearly completed the moulds (I have no shame in thanking nick j c for his excellent inspiration). I just hope mine works as well as his.
I have today also cut and laid the thermalite blocks. They have approx 1-2mm spacing in between.
Also a few larger gaps round the edges, where the inner brick surface is a bit uneven.
Can anyone please advise if these gaps are ok, or if I need to have a other go with the thermalite blocks? I have some kiln dried sand I could use, if that is a good option (especially around the edges)?

Tony

[david s]

The gaps are actually beneficial as they allow the passage of moisture. Did you make some weep holes through your supporting slab so moisture can escape downwards?

[TonyPizza]

david s I did indeed, thanks.

[TonyPizza]

Nick J C Ok, I have been cracking on and I am going to get the sand mould and hopefully the initial cast done too. Thanks to the many who have responded and helped so far. Heck, it's a challenge isn't it!? Thanks to Nick JC for the design ideas.
So, tomorrow, I am hoping to do the following:


Fit gallery and flue mould and add plastic 3mm shims to drop mould when ready to release.
Make sand mould.
Add a few layers of cling film to the sand mould.
Use vegetable oil to lightly lubricate gallery mould.

Make home-brew cast...

What is the best process for measuring the 3% weight of stainless needles required? Do I need to weigh each batch of mix then add the relevant amount, before I dry mix it all?
How do I judge the amount of burnout fibres I need?
How long shall I leave it before I take the sand out?
Do I need to keep the cast damp? If so, How long for? (I have all the other materials ready to apply).

Thanks again for any help in advance.

[Nick J C]

Good luck, all I would advise is that you should expect the mould to be taken apart to get it out, if you are expecting it to drop off the shims and slide out elegantly you will probably be disappointed. I unscrewed mine and bent the sides in and waggled it around, and it came out....others as you can see have been less lucky.

I used a small bucket to approximately measure volumes, and weighed out the needles once to get some idea of how much was needed for subsequent mixes

I just put a handful of fibres into each mix

I wrapped my dome in packaging wrap, similar to cling film, which held in the moisture. I left my sand for 48hrs.....I guess the longer the better, as it will keep it moist. I would remove the paint tin earlier as this was a pig to remove when fully cured

[david s]

A few questions there Tony, I’ll do my best.
Use some digital kitchen scales to weigh a batch of dry mixed homebrew, say 10 litres then take 3% of it by weight and see what it’s volume is. Then you can make up batches by volume easily.
The polypropelyne fibre addition is around a handful for every 10 litres of mix. Be careful to mix really well as they take quite a while to disperse. You don’t want clumps of them in the mix.
The sand can be removed after a day or two and you want to fill any voids while the casting is still damp. After that task has been done the casting should be kept damp for at least a week to enhance strength, after which it needs drying in the sun and wind, weather dependent for a week.

[TonyPizza]

DavidS Thanks for the advice, again!
Today, I built the sand dome, with a few bricks as bulk.
This was fairly easy.
I found the cast to be a bit difficult.
I got the mix too dry for the first batch and too wet for the last three.
The cast is probably thicker than 5cm too... maybe 5-8cm from thinnest point to thickest. Is this ok? I’m guessing it will mean more time to dry.
Can anyone advise on what is the best way to keep it wet for a week? I’ve read about a blanket, not sure how wet it needs to be, of this is the best option?
I guess it’s fingers crossed time now.
As much as today was a bit frustrating and probably a bit rushed on my part, I couldn’t imagine it being in the slightest possible without finding this forum.
Tony.

[TonyPizza]

Hmmm... should I be worried?
I have come to take a look at the cast this morning and there are a few large cracks.
It it possible they have occurred because of the way I applied the mix?
Its still not completely solid, so should I try and manipulate the area either side of the cracks to try and fill them in / make them disappear?david sNick J C any advice would be greatly appreciated at this point.
Really hoping I don’t have to start again.

[TonyPizza]

Nick J C Another update: I have removed the wood moulds (relatively easy, thanks again to some advice from Nick J C). The crack along the edge of the gallery actually goes all the way through rom outside to inside. It all seems sturdy enough.
Given that I want this oven to be about for a long time, I am genuinely thinking I could scrap the casting, buy it all again and start again, but I'm really hoping someone on here will say "it's fine, don't worry"...
I have manipulated the area around and over the cracks on the outside of the casting (I still haven't taken the sand out to check the inside as yet) and with a bit of water and some rubbing, the cracks can no longer be seen.
I guess my main worry is the cracks do go all the way through from outside to inside and that this is terminal.

[david s]

The home-brew contains a high proportoion of clay so is more prone to shrinkage cracking than castable refractory. If the mix was a bit wet the shrinkage is increased. Get to filling the cracks ASAP while the casting is still damp Remove the sand and treat the dome likewise from both inside and outside. I use hessian bags to keep in the moisture but anything will do. Cover also with a tarp.If you use a wet blanket you could also keep it for parties (joke). The casting should be kept damp for a week to enhance strength.(see attached pic) It looks like you've done a pretty good job.

[TonyPizza]

DavidS thanks so much, again. Please tell me, shall I just mix a little more mortar and go over the cracks, as they are so small, I wouldn’t be able to get anything ‘into‘ them.

[david s]

DavidS thanks so much, again. Please tell me, shall I just mix a little more mortar and go over the cracks, as they are so small, I wouldn’t be able to get anything ‘into‘ them.

Sieve you mortar to remove the larger grains of sand. This will enable you to fill the smaller cracks. Rub the stuff in as hard as you can to force it as deep as you can.
As they say there are two types of oven owners, those that have cracks and those who lie about their ovens having cracks.