Chimney design, brick or casting refractory

[cmendezg2000]

Hello there,
I´ve been busy with the brick work of my new oven, for a moment I thought I was never going to finish. I share a few pictures of the building process. Please feel free to point out if catch any mistakes.

Now I come to the community for help, I need to build the chimney, my oven has in ID 105 mm so i´m going to buy a 8" SS double wall pipe, but I don´t know if I will be building the base from bricks or castable. Does anyone here have any experience doing molds for castable that can share some knowledge or to point me to the right direction?

[cmendezg2000]

I¨m trying to upload but don´t let me, it says the extension doesn´t match, it is a jpg thought.

Does anyone know what´s the problem or a work around?

[cmendezg2000]

The issue were the size of the photos, please feel free to comment on the building process and help for the chimney design or build. Thanks

[brad mole]

That looks very nicely built, im just about at the same stage as you, i have my dome built and just about to start the outer arch and chimney transition, but im not sure n the best method, in my mind i would think im going to build up the arch using firebrick and transition that to a square opening, which i will then hopefully find an 8" anchor plate similar to the image attached which the stainless insulated chimney can attach, from the anchor plate up i will use my decorative bricks. im hoping this is the correct way to go but im not so confident that the flow will be right as it will get trapped in the lower part of the anchor plate, unless i cut the lower circle off and just keep the flat plate and 8" connector on?

Anyone able to help us out here if they have done similar?

[UtahBeehiver]

Brad I personally do not see the need to cut the bottom portion off. I used this type of anchor plate attached is a pic of the bottom and top side of the plate and brick.

[JRPizza]

I did like Russell and left the bottom flange intact. I just radiused out my opening like shown and slid the adapter down into the hole.

[brad mole]

great thanks guys i think il do like russell has and curve the bricks!

[cmendezg2000]

JRPizza how did you attached the anchor plate to the bricks? I see that you have some screws? ho did you screw them into the bricks?

[JRPizza]

I had seen designs that sandwiched the adapter between two layers of bricks, ones that used expanding type bolts in blind holes in the bricks, and some that just used mortar to bond the adapter in. I thought all those options had drawbacks, and I worked for years as a fastener and assembly engineer for Boeing, so I decided to drill holes through the bricks and make a semi-standard bolted joint. There are pictures of how I did this on my build thread - I attached a link to the post with the pictures below. I modified the bolts (used corrosion resistant steel) by cutting slots in the threaded end. Used a masonry bit to drill the holes in the brick, then inserted the bolts and put nuts/washers on to hold them in place, then mortared the bricks in place (see picture 4 in the post to get an idea of what i did). The slots in the end of the bolts allowed me to remove the nuts and install the adapter without the bolts spinning during tightening. Keeping the four bolts in the exact location to match the hole pattern in the adapter is tough as hole placement, angularity, and mortar thickness all can change alignment, but I only had to slightly elongate two of the holes in the adapter to get it to fit up. This design will theoretically allow me to remove the chimney and adapter if ever needed, but I doubt I will ever have to.

[david s]

If you want to go the cast route it is pretty simple. You fill the entry with broken polystyrene fruit boxes then top with damp sand formed to your desired form. Use castable refractory to trowel over then remove polystyrene and sand after 24 hrs. Compound curves are a piece of cake.

Regarding anchor plates, I don’t use them. They are expensive and introduce problems in attachment. Highly conductive materials like stainless will expand before the refractory that surrounds it and produce stresses that can cause cracks. Any fixings other than stainless are likely to corrode. Drilling or cutting bricks is likely to increase the chance of cracks occurring there. I now simply cut three tabs in the base of the flue pipe and insert it into the casting which is slightly larger than the flue pipe to allow for expansion. This can easily be done by wrapping some cardboard around the pipe so the diameter is around 2 mm bigger in diam. Cover it in sheet plastic and cast up to it. Remove the pipe when the casting has set (24 hrs), discard cardboard packing, cut and bend the tabs then replace the pipe in the hole in the casting. 10:1 vermicrete seals around the flue to casting joint pretty well.

[cmendezg2000]

Finally I had the courage to go ahead and cast the flue gallery for my oven. This was my first time attempting to do anything like this, and to be honest, I panicked for a moment. I had two 25 kg refractory concrete bags, 50 kg in total, I thought that it was going to be more than enough, to my surprise it wasn´t, so, I had to stay a bit lower respect to the initial plan, and because of this, I thin I will not get a super level surface to anchor the chimney plate.

I need some advice on how to level/attach the plate once the concrete drys. I was thinking of doing a row of bricks like JRPizza and UtahBeehiver suggested on this thread, levelling underneath with refractory mortar or refractory concrete (I don´t think the concrete will attach to the dry concrete, what do you think, maybe mortar is better).

This afternoon I will remove the plywood frame and see what my flue gallery looks like. If is ugly, it is ok to shape the corner a little bit with an angle grinder? or it is just better to leave it as it is?.

Tomorrow I¨ll be posting the photos of the result.

[cmendezg2000]

Once I removed the plywood form, here is how it looks like!
Being this the first time I try to cast something, I don´t mind the ugliness as long it is functional.

If someone has ideas of how to make it more pleasing to the eye, please share your knowledge, it will be super appreciated.

[david s]

That looks fine to me. So much easier and quicker than building it in brick.It will be covered by insulation anyhow.

[cmendezg2000]

Hi david s , thanks for your approval, that´s kind of a relief to me.

Are you talking about insulation on the flue gallery of the chimney?, I know the fumes are really hot, but does it need insulation? You mean FB and then Perite crete render on top? I wasn´t planning on doing any.

[david s]

The flue gallery doesn’t get as hot as the dome, but being hot on the inside and cold on the outside produces uneven stresses that can lead to cracking. Once you have insulated over the dome the gallery will be almost half covered anyhow. I don’t cover it with blanket but do have a thin layer of vermicrete or perlcrete over it to integrate the form with the dome. You will see what I mean once you start insulating the dome.