New 36inch castable build in Brisbane

[brissie]

Re: New 36inch castable build in Brisbane

Thanks for the comments mikku,

I think because the paper was wet and only a couple of layers thick, I should have gone a lot slower. Note that the imperfections are not deep. More care is needed to keep the paper stable. I think functionally it would work as is, but I will try and clean it up a bit. You can also see the texture change after around the first 100 mm, so the amount of water added does make a difference.

Perhaps I should have added more water. but this also reduces strength.

[mikku]

Re: New 36inch castable build in Brisbane

Mikku,
It's now 6.23 am I've been up for about an hour.
Maybe you should try two alcohol free days a week. It works pretty well.

david s--
I misread your post this morning when my eyes were not functioning yet. I thought you said "try two alcohol free drinks a day for a week"! A little different from what you said!

Cannot do that either! Never drank alcohol of any type until I quit smoking in 2001. Needed to replace one bad habit with something else--you know, have to keep those hands busy and feeding something into your mouth! So, tried a drink occasionally ... Now need to try catching up with 53 years of being dry... Two days alcohol free and that throws my calculations off to sometime when I am well over 100. Not an impossibility in my family--many family members have lived almost to 100!

Thanks for the advice though, does that work with those devices you use for making wine from different juices? The wine should be good enough to drink daily and almost any time of the day as well--maybe not breakfast??? but if for breakfast you could call it breakfestival!

[mikku]

Re: New 36inch castable build in Brisbane

Some photos

Brissie- I thought that the surface would be a lot smoother than what you ended up with. Maybe the problem with this sand method of molding is that you cannot vibrate the materials once they are placed to get the glassy finish from a hard mold.

Probably will not cause any problems along the line, they look better than a lot of castings shown previously.

There are two types of refractory available here--maybe a whole lot more--but the asahi stuff has a trowel grade and a pourable grade. The pourable stuff has chunks of crushed firebrick (maybe) as the course aggregate. Maybe the trowel grade could be used to skim coat the interior of your dome. I do not know if there would be any problem with adhesion. This is the stuff I used when I joined my sections prior to doing the insulation thing. It still is a little grainy but it sets quick and hard.

It is interesting to see what issues arise when you are doing a castable dome. I spent a whole lot of time on forms--like 10 days! But much of this time was simply scratching my head trying to determine how to do a trapezium that would be freestanding--both inner and outer molds that maintain an 80mm space...then try to determine the best way to fill to avoid airpockets and the problem you face now.

I actually started posting on this forum after my forms were poured--too late to make major changes, but if there had been something drastically wrong, I could have torn back the form and made adjustments. The only issue I see with mine that I would change would be to shorten the landing as much as possible. Probably also a larger oven as well.

I have plans to do another oven this winter when things slow down. Now no time to even pass gas politely.

Keep up the good work--a great build in the making!

Another thought on the sand method of molding. It might be possible to first trowel on a 12-15mm layer of refractory (onto the sand mold initially). The stuff begins to set very quickly--when you have the trowelable 1/2 set, then begin with the pourable stuff that you could hand pack on the dome. That way, the inner surface would be glassy and there would be something that the pourable could bond to instead of just waxed or wet paper!

But that is just a thought?

[brissie]

Re: New 36inch castable build in Brisbane

Some photos

[brissie]

Re: New 36inch castable build in Brisbane

I have taken the casts off the moulds.

There is some crappy bits. The mix was on the drier side. So I did expect I would need to do some patching. After the first batch, I decided to put to much on in one go... causing the paper to slip down and fold into the castable. Now I have paper embedded about 6mm in places. Some paper I could pull out, some not.

The dome is thick 80 mm, so I don't think will cause structural issues, but not sure of the best way to fix it. Do I run the grinder along and create a V, to remove the paper, then patch? If I patch over the embedded paper will it cause issues? will it burn out? Air gaps? explode?

Not sure I am fussed on exploded castable topping on my Pizza :-)

[david s]

Re: New 36inch castable build in Brisbane

Ok, that's correct. Sorry to worry you.

[brissie]

Re: New 36inch castable build in Brisbane

Brissie,
I just reread your thread and was a bit concerned when I read that you said the castable was a "bit spongy". I'm concerned that you may have used insulating castable instead of dense castable. If you used insulating castable it will take much longer to get heat into the oven. The density should be around 2000 kg/m3. Check your specs.on your product.

Just checked,

Approx Weight Required for Casting ,kg/m3 = 2000
Bulk Density After Drying at 110?C kg/m3 = 2110

It is heavy, not like air filled insulation.

[david s]

Re: New 36inch castable build in Brisbane

Brissie,
I just reread your thread and was a bit concerned when I read that you said the castable was a "bit spongy". I'm concerned that you may have used insulating castable instead of dense castable. If you used insulating castable it will take much longer to get heat into the oven. The density should be around 2000 kg/m3. Check your specs.on your product.

[mikku]

Re: New 36inch castable build in Brisbane

Mikku,
It's now 6.23 am I've been up for about an hour.
Maybe you should try two alcohol free days a week. It works pretty well.

That is what I call coffee and water, but they are used in moderation!

Caffeine isn't good for your health, and too much water and you can drown. So have to be on the safe side and use in moderation!

So you are an hour ahead of us! Its 5:50 here now and been up since 3:45, hands are sore from using tye wraps to attach pex A tubing to rebar for a little floor heating job.

[david s]

Re: New 36inch castable build in Brisbane

Mikku,
It's now 6.23 am I've been up for about an hour.
Maybe you should try two alcohol free days a week. It works pretty well.

[mikku]

Re: New 36inch castable build in Brisbane

Mikku,
Does this mean that you are now convinced of the economy of the sand mould method?

David s:
What the heck are you doing up at this ungodly time? Thought that only us nut cases in Japan are running on all cylinders at 4AM (or at least this is when my engine got started).

As for your question, judging by the build in this thread---It is hard to deny the economy of a sand mold method. But it is "all to do" with the craftsmanship put into the preparation! That is true for any style build though.

I might be "hard headed", but there is still a little pliability in what gray matter is left after being bombarded with alcohol molecules on a daily basis!
I call it "anti-freeze"!

[david s]

Re: New 36inch castable build in Brisbane

Mikku,
Does this mean that you are now convinced of the economy of the sand mould method?

[mikku]

Re: New 36inch castable build in Brisbane

Mikku,

I am just a guy that has used a lot of information from this great site. It's the people who support the forum, and answer questions, and been around a long time that have made this site what it is.

It don't matter how fast you can make an oven. As long as you have fun. And I am having fun, and don't mind sharing the build. I hope people like it. I think its all about sharing, not enough of this these days.

Me - I am the guy in the middle, flanked by my son and neighbour. Who may be looking at building an oven also.

Brissie,

You have a great attitude and a lot of abilities. It is fun just watching what you are doing. You must have been a pretty good plumber, carpenter and other tradesman along the way. I hope you son is picking up what you have learned during your lifetime.

[stonecutter]

Re: New 36inch castable build in Brisbane

..... It's just that if you plan for it you can you can reduce design downsides before building it in permanently. Efficiency and heat retention should be considered high on the list.

Agreed. Which is why I said it doesn't hurt to add a break, since it has no structural impact or involve any additional planning outside of an inch or so more to the final front dimension.

[brissie]

Re: New 36inch castable build in Brisbane

I have two breaks, the vent area is independent of the oven and the outer arch. The vent arch does not need to be tied into either of the latter sections, it does not strengthen the arch, because it is self supporting.

Correct that if you have a direct connection between the vent arch and the oven wall it will draw heat, and a break will help slow that action down...I doubt that a 1/2"-1" break will stop conductivity completely though. Loss of heat without a break between the oven and vent might not be measurable but it certainly won't hurt anything by doing it. The greatest benefit to a break (IMO) is between the outer arch and the vent walls, because almost all finish material does not have refractory qualities.

As far as the vent being a heat sink, my view is that as soon as the heat that is radiated by the fire and stored in the masonry of the oven passes through the oven opening, it doesn't matter if it is absorbed the vent or the flue...it is lost to the oven anyway.

Thanks stonecutter,

I checked out your build. Its truly impressive! I don't know you manage to carve granite, its so hard. The look is fantastic. I can see your separation on both sides of the flue gallery, so will try and do this in my build.

Yeah, I don't think my aim is for perfect heat isolation, and I don't know how long heat will be retained for example slow cooking, or bread ... etc. It's just that if you plan for it you can you can reduce design downsides before building it in permanently. Efficiency and heat retention should be considered high on the list.