Planning my 32" cast oven

[UtahBeehiver]

NIce cast job.

[david s]

That looks terrific, you've done well. I've seen plenty of commercially cast ovens with far more voids.

[AndreasP]

Here are some after photos with the lip ground off and the small voids filled.

[AndreasP]

Thanks Kris.

Just took out the sand and bricks. The inside looks pretty good. Just a few small voids. I attached some photos, one has a penny for comparison next to one of the larger voids.

The major issue I had was that the form for the opening to the dome must have been to shallow. When we pressed in the Homebrew it must have slipped behind the form, so there is an extra lip.
I took an angle grinder with a diamond disk and cut off most of it, then used a grinding disk to grind off the rest. Worked OK, but lots of dust even though the concrete was still pretty moist.
Definitely easier to work with fresh concrete than when it's fully cured.

Initially I wasn't going to fill the small voids, but did it anyway. Not sure if it was necessary. Once I started filling, I could just keep going. Every time I look I find more and smaller voids.
Pressed in the mix with a flexible putty knive, then scraped it off and smoothed it over with my finger. Seemed to work pretty well.
Covered it up again. Will try to cast the gallery tomorrow evening if I get a chance. Otherwise it will have to wait until the weekend.

Photos attached are without any filling. After photos in the next post.

[Kris S]

Looking really good!

[david s]

Wasn't able to build the form for the gallery today, but took off the front template so that I can reuse it for the front of the oven.
I think I need:

• For the entrance to the gallery I will reuse the same template but add to the bottom, so that it can sit in front of the firebricks
• For the end of the gallery that abuts the oven opening, I will make a new template, 1 1/2" narrower and lower

This gives me a 1 1/2" recess against which I can rest the door and a 1 1/2" thick gallery.
I actually made a mistake when I first cut the template for the dome opening and made it only 1 1/2" larger than the opening itself. That's why the duct tape is there.

I can see some voids on the face where the gallery will connect. I'm not planning on doing anything with those voids. Most of them will be covered by the gallery.
Will be interesting to see how many voids I get on the inside when I remove the sand.

Covered it back up with a wet linen and a plastic sheet to keep it moist.

You won't really be able to tell until you remove the newspaper strips on the inside of the oven chamber.You need to force the mix into the voids, an old butter knife works well. The mix needs to be fairly stiff, if too wet it shrinks away. Peanut butter (smooth not crunchy) consistency is what you want. Sieving out the coarse sand is also important.(#30 way too coarse imo)

[AndreasP]

david s , how do I make sure that when I fill any voids on the inside the patches don't fall off into my pizza?
Here is what I have found in other threads:

• make sure the casting is still moist
• maybe moisten the casting a bit
• screen out the larger sand (I have #30 sand, which already is quite fine)

I assume there is a tradeoff between not filling small voids and running the risk that something does not bind properly and falls off at some point.
Maybe only fill large voids (but then again, what is large?).
What is the reason behind filling voids at all? Is it necessary or just cosmetic?

If the voids I end up with are similar to the ones on the front face in the picture in the post above, should I fill them or just leave them be?

Any insight and recommendation would be very much appreciated!

[AndreasP]

Wasn't able to build the form for the gallery today, but took off the front template so that I can reuse it for the front of the oven.
I think I need:

• For the entrance to the gallery I will reuse the same template but add to the bottom, so that it can sit in front of the firebricks
• For the end of the gallery that abuts the oven opening, I will make a new template, 1 1/2" narrower and lower

This gives me a 1 1/2" recess against which I can rest the door and a 1 1/2" thick gallery.
I actually made a mistake when I first cut the template for the dome opening and made it only 1 1/2" larger than the opening itself. That's why the duct tape is there.

I can see some voids on the face where the gallery will connect. I'm not planning on doing anything with those voids. Most of them will be covered by the gallery.
Will be interesting to see how many voids I get on the inside when I remove the sand.

Covered it back up with a wet linen and a plastic sheet to keep it moist.

[david s]

Yes, that’s a reasonable plan. It gives you easier access to fill any voids without the gallery in place. You will need to make a larger template for the front of the gallery.

[AndreasP]

Will wait anther day.
I am planning to build a form for the gallery today.
I will cast the gallery in place in front of the oven after removing the sand from the dome. It will be easier to remove the sand and bricks without the gallery.
The gallery and form should close up the dome again so that it will stay moist on the inside.

[david s]

Either or, providing the casting is still damp, filling the voids should be ok either way. Not sure what your sand is like, but you will find a finer mix is better. You can do this by simply sieving out the coarse grains.

[AndreasP]

David,
thanks for the comments. Yes, I understand that the volume gets reduced. But the spreadsheet i used (from this site) was trying to take that i to account from what I can see. I'll have to take another look at it just out of curiosity.

Yes, am planning to keep it covered to cure damp.

Are you suggesting to leave the sand in for the week of damp curing? I think I read that i should remove the sand on day 2 so that I can fill in any voids if there are any.

[david s]

Great job. Regarding quantities remember that when the finer materials (cement lime and clay) are mixed with the coarser ones (sand) they will fill the voids so you end up with a reduced volume. In addition the volume will further compact when water is mixed with the dry mix to make the workable castable. Perhaps this was not taken into consideration with th spreadsheet calculator.
As the home-brew contains portland cement it should be damp cured for at least a week, so keep it well covered if you remove the sand.
As you've found, the consistency is hard to attain, too wet and it will slump. too dry and you'll get more voids. The next one you build for a friend will be far easier.

[AndreasP]

Looks like I used more material than what was in the Excel calculator spreadsheet I was working with.
The spreadsheet came out to 25 gallons of dry mix for the dome and the gallery (before blending the 3:1:1:1 mixture together).

I ended up using 6 x 5 gallon buckets filled to the brim (30+ gallons) of dry material before mixing it, and that was only for the dome.

According to the spreadsheet the gallery should use approx. 15% of the material used for the dome, so I'm hoping that one 5 gallon bucket will be enough for that.

[AndreasP]

Cast the dome yesterday. Wrapped it in a wet blanket and covered it with plastic. Rain is forecast for today.
Will let it cure until tomorrow before I remove the door mold and sand to check out the inside.

Used almost 200 lbs of sand for casting the dome.
Used a bit less than 1.5 parts of water in the 3:1:1:1 Homebrew.
I mixed the dry materials including the SS melt extract needles and the polypro burnout fibres in cement mixer, then poured it into a tub and added the water and mixed by hand.
Ended up using 750ml of SS needles and a handful of burnout fibers per 5 gallon bucket of dry mix.

I felt it was a bit difficult to get the right consistency. The first batch was a bit too wet, so the first layer has sagged a bit. The second batch was maybe a bit too dry, making it more difficult to press it against the form.

We'll see how it worked when I remove the sand.

Pictures to follow. Looks like a big blue tap at the moment