Chimney design, brick or casting refractory

[cmendezg2000]

To answer JRPizza , I found before the pdf instruction that you attached, but it doesn´t say much, if you look to page 20, mine is like the drawing in the bottom left of the page, I know it says that it twists but I can assure you that is not, there must be some kind of mistake. Anyway, if I´m still missing something it doesn´t matter, I´ll find a way even if its not the intended way, it just needs to sit on top tight that it doesn´t blow off.

To david s , I saw your answer yesterday in the other thread, when I saw it I immediately knew that you had answer already the questions. Just one more thing though, after the vermicrete/perlicrete layers application, you said that you do a strong thin shell for strengthening, what is it? cement + sand + lime without the perlite?

Now I¨m ready to render, so I will follow david s suggestions.
I will do a total of 50 mm of rendering, I think that I will do it in two to three goes to make it easier, what do you think?

[david s]

I installed the anchor plate, at the end I decided to screw it directly into bricks, the reasoning behind this, is because if there is a failure due to the screwing or the dilatation of materials I can repair without damaging the refractory castable or any structural part of the oven, Ill just take those bricks out, replace them or try some other method.

I show you a photo with the chimeny installed, then I took it down until I finish rendering the dome.


Also I started with the insulation blanket, but I didn´t have enough, I jump this afternoon to my supplier to get some more. Tonight I hope to finish installing the blanket and the chicken wire to start the rendering tomorrow.

For the rendering, I have mix information, there are different ratios that builders use, going from 5/1 up to 10/1 (I¨m using Perlite, that´s what I can find). Which one do you recommend and why? Could you please share your whole formula and ratios (Portland cement, Perlite, lime, etc.). Also, I have space for 4 inch insulation, I was planning splitting it 2" blanket and 2" perlite render. What´s your take on this?

Also I finish installing the tile work around the oven, so when rendering sits directly into the tiles.

I hope the screws are stainless. Screws do have a tendency to work loose because of the expansion and contraction. The flue gallery casting looks good. I now see from the pic why you won’t be able to insulate it at the front as it’s flush with the decorative brick arch.

Perlite/ vermiculite, some info here.
https://community.fornobravo.com/for...45#post411045i
Be sure to wear gloves if applying by hand. I use a 10:1 mix over the blanket because I want additional insulation there. I then do a strong thin shell rendered over that using a cement render (no vermiculite) as the addition of vermiculite or perlite will compromise the strength of the layer. This is not the only way to do it however, some folk have had success rendering straight over the blanket using a richer vermicrete as the final layer.This table will also help explain relationship between strength and insulation value. It is best i've found, to do the drying fires before the final layer. This makes water elimination a bit easier.

[JRPizza]

If this is what you have it looks like it is twist fit too - see page 20
http://www.shastavent.com/assets/SV_...ions_v1.10.pdf

[JRPizza]

Mine was threaded. Is Shasta the brand of pipe or the store you bought it?

[cmendezg2000]

Does anyone knows how to install the chimney cap? As you can see in the photos, the cap has some kind of legs, but it doesn´t seems to fit anywhere. If the legs weren´t there, the internal diameter of the cap fits perfectly into the pipe, but before cutting them out I ask the community if anyone knows how to install this particular model.

This pipa + cap I bought them from Shasta Vent.

[cmendezg2000]

I installed the anchor plate, at the end I decided to screw it directly into bricks, the reasoning behind this, is because if there is a failure due to the screwing or the dilatation of materials I can repair without damaging the refractory castable or any structural part of the oven, Ill just take those bricks out, replace them or try some other method.

I show you a photo with the chimeny installed, then I took it down until I finish rendering the dome.

Also I started with the insulation blanket, but I didn´t have enough, I jump this afternoon to my supplier to get some more. Tonight I hope to finish installing the blanket and the chicken wire to start the rendering tomorrow.

For the rendering, I have mix information, there are different ratios that builders use, going from 5/1 up to 10/1 (I¨m using Perlite, that´s what I can find). Which one do you recommend and why? Could you please share your whole formula and ratios (Portland cement, Perlite, lime, etc.). Also, I have space for 4 inch insulation, I was planning splitting it 2" blanket and 2" perlite render. What´s your take on this?

Also I finish installing the tile work around the oven, so when rendering sits directly into the tiles.

[david s]

When you said refractory concrete I assumed you meant castable refractory which is the correct product to use. This is designed for casting sections and is different to refractory mortars designed for thin joints between bricks.
Regarding the fixing of the flue, here is a pic of a method of fixing the flue pipe without using an anchor plate.You can cast around the pipe before cutting the tabs, but first wrap some cardboard about 1 mm thick around the pipe to allow for expansion against the casting. Failure to do this can result in cracking the casting because the higher conductive stainless pipe will expand first. Also wrap some plastic around it for easier removal after the casting has set.
Fixing an anchor plate is fraught with problems. eg drilling holes in castings issuing for cracks to develop there. Any steel fixings (screws, anchors) that are not stainless are subject to corrosion because of the heat and also any metal fixings are going to expand faster than the surrounding refractory and then loosen when cooled.Sandwiching the anchor plate between two layers of brick is about the best solution I've seen to attach an anchor plate.

[Sampatch]

Re: Plywood. If you drill out center ply do wood you may be able to drive it out toward the dome. Removing ply may loosen fit just enough.

Re: Arch crack and gap. The mortar sort of looks like premix refractory mortar. If so, it is only intended for thin mortar joints. It is also air dry and heat cured versus chemical cure like firebrick mortar. Refractory mortar is not good for any wet areas. Firebrick mortar works perfectly in smoke chamber and reveal area and won’t wash out in rain.. It also performs better on wider joints such as you have. If you try to fix crack again, get firebrick mortar if you haven’t used it.

[cmendezg2000]

1. Yes! I do have a piece of plywood stuck in the inside part of the flue gallery, I have tried to remove it but with no luck. This weekend I will take the time to do a proper job, but definitely is not staying there.

2. The crack in the front arch. I took down and up the arch like 5 times, always a crack appeared, this is due to the mortar joints being a little thick. At the end I decided to leave like that as the bottom part of the bricks are in compression, so the arch is strong and it could be standing even without the mortar; anyway, I poured some refractory concrete on the back of the arch where you cant see it, maybe is doing nothing to help, I dont really know. After I did some tests by putting weight on top of the arch and hold really well. But if you think that I could fix, just let me know how, because at this point I have no idea.

3. About the anchor plate fixing, yesterday I tried to do a transition of bricks from the concrete arch, and then attach the plate to the bricks instead of the concrete. I failed miserably as I don´t have a leveled surface due to the fact that I was lacking of concrete at the time of pouring. I thought that I could level it putting bricks and mortar, but while I was doing it I stopped and took it down, the same principle as the arch apply here, if I level the bricks with a thick layer of mortar it would crack, and it will result in a weak base for the chimney. So I¨m kind of stuck here at the moment. I think I need to grind the concrete to level it, unless somebody has a better idea.
Here is the photo of the uneven surface, is not super clear, but I have a difference of nearly 7 mm from front to back, and around 5mm between the sides.

I appreciate your help. Make sure to follow along my feed, I hope to finish the oven in the next couple of weeks.

Best regards

[david s]

Yes, you should remove that formwork (well spotted). It is a mistake to do the drying fires on an uninsulated oven IMO as the huge difference in inside and outside temperatures can lead to cracking. You might be lucky and avoid it, but then again you might not. Uninsulated flue tiles and chimneys thatare subjected to flame impingement often crack, but if insulated hardly ever do. The downside is thatmoisture takes longer to get through the insulation layer.

[Sampatch]

A couple of comments for your consideration. I enlarged your cast photo and noticed plywood for is still in place between casting and the oven arch. This space is normally insulated with non combustible gasket. If it can be removed it should be. Or, you may be able burn it out. It also looks like you have mortar crack at top joint of your inner arch. It may not cause a long term problem; however now would be a good time to saw the cracked mortar out and tuck point new mortar in the gap,or remove the brick and reset it if possible beneath the cast in place smoke chamber.

[cmendezg2000]

Hi david s , I totally understand, thanks for point it out. If everything goes as planned, I starting the insulation this weekend.

By the way, the brick work I finish it like a month ago, in this part of Mexico winter is a joke, is like spring/summer time, so its been sunny almost everyday with a temperature that goes from 10°C up to 30°C. The oven looks super dry, no signs of moisture and even so, I know that it must have still lots of water in there. I could start curing the oven at this moment, and when I start to apply the insulation layers of perlcrete stop curing with fires, and let the insulation to cure for a week before I re start the fires?

[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.

[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]

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