36" Pompeii Dome Chicago

[david s]

Ok, that’s good dense castable. It should also contain burn out fibres to assist water elimination. Build a sand form, cover in strips of wet newspaper and form your casting. Don’t mix up too much at a time and wash barrow and spade between batches. It will not need extensive damp curing like normal cement products. CAC castings Aquire full strength very early so cover for a couple of days only before de-moulding.

[Chach]

Ok, that’s good dense castable. It should also contain burn out fibres to assist water elimination. Build a sand form, cover in strips of wet newspaper and form your casting. Don’t mix up too much at a time and wash barrow and spade between batches. It will not need extensive damp curing like normal cement products. CAC castings Aquire full strength very early so cover for a couple of days only before de-moulding.

thats correct about the burnout fibers i asked about that wjen i purchased because i was going to add but I was told they are in there already I had the opportunity to use a premixed castable so I said what the hell lets do it...you sir, you know you stuff!

[Chach]

david s what thickness shall I cast this piece? I was thinking 2" but is there a maximum thickness and a minimum thickness?

[david s]

1” should be good. Mine is thinner than that in places.

[Chach]

if I run out and i need to make more castable how much time do i have between batches

[Chach]

Ok, that’s good dense castable. It should also contain burn out fibres to assist water elimination. Build a sand form, cover in strips of wet newspaper and form your casting. Don’t mix up too much at a time and wash barrow and spade between batches. It will not need extensive damp curing like normal cement products. CAC castings Aquire full strength very early so cover for a couple of days only before de-moulding.

ok so I already had a sheet of styrofoam that i cut out into the shape of the vent arch. The chimney is tall right now but i will cut that down before i cast. I didn't end up going with the sand because I had this styrofoam already so I figured I'd use it for something. I will put wet newspaper over all this and I will attach it to the vent form i made before I decided to cast this piece. this way it will keep the profile if my arch I intended. You don't see a problem with this set up right? its the same thing but without the sand. I plan on putting no more than 1 1/2" on this with a 1" being my minimum. after i cast it i will wrap it in a wet towel and after 48hrs i will remove it from the styrofoam and then wait a few days before i mortar it on my oven. should i put cling wrap over the mold then wet newspaper so it slips out of the mold easier? Now i'm interested in casting an entire oven. how many lbs of castable do you usually use to cast a smaller oven say like your 29"? might be a good gift for a friend of mine that helped me move material around and sort my stone when I was installing it.

[david s]

Skip the wet newspaper, cling wrap over styrofoam will be enough, but make it a double layer.

[Chach]

Did the cast we will see how it turns out..its very vertical i probably could have made it a little smaller in height but its going to have a lot of area in there. i would probably do a sand mold next time like david s said I see that being easier than what i did. forming this stuff with a one time mold is useless. The thickness was getting away from me because i put a piece of hard board in front but didn't make it a secure form and the concrete was pushing it out so it was getting thicker as i was going up. i might have to knock down some spots but we will see....first time doing it and i have a better idea now. mixing the stuff wasn't bad with a power drill and bucket using the water specified by the manufacture. i used a little over 6lbs of water like 92-95 ounces of water per 55lbs to cast by hand. we will see in a few days what it looks like. I wrapped it in damp t shirts so i'll wait until friday to demold it and set it on the oven.

How long should I wait to start curing once i get this on, the rest of the oven has been done for over a week almost 2 weeks.

[Chach]

Forgot to post a picture of the flue

[david s]

CAC achieves full strength quite early. Being very temperature dependant this can vary, but give it at least 36 hrs. You can start the drying fires after this, but allowing more time to allow it to dry further from sun and wind is prudent as free water in the cast is your enemy. As it won’t get direct flame impingement from your drying fires, you shouldn’t have any problems. Generally, if you see steam, you’re going at it too hard, back off. If you search the product information of the castable it should provide a firing schedule you can use as a guide. I’ve found that the recommended water addition for castables is lower than that required to make up a nicely workable mix. If you have an enclosed mould and can ram and vibrate the mix it’s ok, but if you don’t the mix can end up too loose with quite a few voids. More water will fix this problem although too much can result in a weaker product because it can increase the volume too much. Sorry, I should have warned you of this. I think you’ll be fine, if on demoulding you find some voids, sieve out the course aggregate from some castable (hope you have some left), mix it with a little water to a peanut butter consistency and force it into the voids. This operation needs to be done while the casting is still damp.

[david s]

Forgot to post a picture of the flue

I think your form is great. Not only will it deal with smoke issues it’’s going to look great once insulated and stuccoed.

[RandyJ]

Looks like a interesting approach. I will maybe have to keep that in mind when i start my next oven. Looks good can't wait to see it installed.

[Chach]

So I unmolded the flue cast....not bad a little honeycomb inside in one spot not bad but I dont think it will affect anything. the form came out rather nice and I can reuse it again if needed. i just hit the top through the 6" opening with a rubber mallet and then tapped the styrofoam gently until it popped out. i meed to cut 2 firebrick and set them before i set this on top. Probably way big for my application bur there is for sure a lot more area there than if I did brick and a hell of alot of less headache and time. Arches and flue done at the same time. I think this is the way to go.

[Chach]

Set the flue archway today worked like a charm and I'm very happy with the result. Thanks david s for your help with putting me in the right direction. I will say it again this is the way to go for this piece. I habe tons of area for the smoke to accumulate i don't have to worry about the archway falling apart. I still went with brick sides so I still get the brick vent area and once I do my enclosure you won't even see it.

Should I insulate this flue as well. the problem i have is the front is flush with the enclosure so i will be sticking my face stone directly on the flue and wont be able to insulate the front..is this an issue? i guess ill use homebrew to stick those on or is regular mortar suffiencent since it doesnt get that hot. ? I did my fireplace like that i stuck the stone over the firebrick face with regular mortar so far so good.

[david s]

Set the flue archway today worked like a charm and I'm very happy with the result. Thanks david s for your help with putting me in the right direction. I will say it again this is the way to go for this piece. I habe tons of area for the smoke to accumulate i don't have to worry about the archway falling apart. I still went with brick sides so I still get the brick vent area and once I do my enclosure you won't even see it.

Should I insulate this flue as well. the problem i have is the front is flush with the enclosure so i will be sticking my face stone directly on the flue and wont be able to insulate the front..is this an issue? i guess ill use homebrew to stick those on or is regular mortar suffiencent since it doesnt get that hot. ? I did my fireplace like that i stuck the stone over the firebrick face with regular mortar so far so good.

Yes you will need to insulate it. A thin casting or flue tile that is uninsulated is bound to crack. In my design the decorative arch sits in front of the flue gallery with a 6 mm expansion gap between the top of the flue gallery and outer decorative arch. Above it 10:1 vermicrete surrounds it over which a stucco coat holds everything together. However you do it, it should be insulated otherwise a hot surface inside and a cold surface outside will be too much for it.
Whatever mortar you use, time wil tell how durable it will be.