New 36inch castable build in Brisbane

[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 :-)

[brissie]

Re: New 36inch castable build in Brisbane

Some photos

[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?

[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!

[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.

[cobblerdave]

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.

G'day Brissie
When I first read you post that the paper had slipped I feared the worst.
Now the pics have eased my mind. That's not that bad at all. Definitly not a bad structural fault at all . As for the look of it, its nice and smooth so doesn't look bad at all. The dome is perhaps the most important part along with insulation.
But the least seen. No one will ever see that " imperfection"
Hang in there
Regards dave

[david s]

Re: New 36inch castable build in Brisbane

Hi Brissie,
I've never had the problem of the newspaper slipping, but then I've only used newspaper and water. As you also used oil this may have caused the problem. Any embedded newspaper will just burn away. You can leave it, the surface looks pretty good to me. If you have any voids to fill you can sieve out the course aggregate from some dry castable and mix a little water to the sifted castable that is left, to a peanut butter consistency. This mix can then be squished and smoothed into any voids. You need to do this operation before the casting gets completely dry. The day after removing from the mould is usually about right.

[stonecutter]

Re: New 36inch castable build in Brisbane

I think a brick oven interior is a lot rougher than that. Ever see the inside of professionally built Neapolitan ovens? Most of the ones I have seen have rough brickwork...your surface is more smooth.

[mikku]

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.

The ratios for the mixture are pretty specific with the stuff that I was using. Think more important is getting the stuff packed tightly when you are hand working it. But this is a guess only. Davids comments on sifting out aggregate from regular mix to make a peanut butter consistency patch material sounds good. The stuff does set overnight so I am thinking it is very important to get the patching done before too long.

As others have said and I agree, nothing to worry about structurally! But just because someone else does not see any imperfections does not make them disappear...you have to satisfy yourself first! If it to your expectation, then nothing else matters!

Keep up the good work.

[brissie]

Re: New 36inch castable build in Brisbane

Weekend #4,

I went shopping for arch bricks today, we picked some that are dark in colour, they are seconds at $1 each. The plan is make the decorative arch tomorrow.

I have the dome in place with heat break number 1 and additional support for the dome 5:1 vermiculite concrete. The CalSill board is only 1 meter wide, so added extra support for 80mm walls.

You can see the 10:1 vermiculite insulating in the heat break. The gap at the top is 2 or 3 mm, and should not be an operational problem. the gap will fill with ash. ( thanks David s for the idea ).

The brick slabs had horrible edges. So needed to take off the edge with the grinder. If I did this again I would look at standard fire bricks, I think they give a better finish. The dome was easy to put together with the help of my son, we stuck the dome together with corfix 900 degree mastic, and did not seal the dome to the base to allow for expansion.

The hole in the top will be filled with castable tomorrow. I will use the remainder of the castable to patch over the joins in the dome. I started with 12 * 20 kg bags. This quantity is about the correct amount for 80mm thick 900mm/36 inch oven.

[brissie]

Re: New 36inch castable build in Brisbane

More photos,

[david s]

Re: New 36inch castable build in Brisbane

Brissie,
Just had a second thought since you were asking about temp in the entry.
My heartbreak is actually between the flue gallery and the outer decorative arch. In that position vermicrete holds up ok , however if you put it between the dome and the flue gallery it is considerably hotter there. If it were me doing a vermicrete mix there I'd use some castable with the aggregate sieved out of it to mix with the vermiculite rather than using a Portland cement mix.
Dave

This area gets pretty hot. It will be hot enough to destroy Portland cement, use the sifted castable.For the mix between the entry and the outer decorative arch, Portland and vermiculite is ok.

[brissie]

Re: New 36inch castable build in Brisbane

This area gets pretty hot. It will be hot enough to destroy Portland cement, use the sifted castable.For the mix between the entry and the outer decorative arch, Portland and vermiculite is ok.

Thanks for the reminder David s,

I was planning on implementing your good advice. I didn't bother with the lower part of first heat break on the floor. If the cement burns away it will still have the vermiculite in place as an insulator.

[brissie]

Re: New 36inch castable build in Brisbane

Filled the hole it the dome wit castable, and first heat break with 5:1 vermiculite sieved castable. I also covered this with a layer of standard 5:1 vermiculite and Portland cement. You can see the expansion joint in the photos.

I also completed the arch.

[stonecutter]

Re: New 36inch castable build in Brisbane

I'm not sure if you are leaving the backer rod in place, but if you do, it will melt. Ceramic rope works well as expansion gasket,and you can slurry paint it to encapsulate the fibers. Looking good..this has got me interested in casting a dome.