Dome Insulation Question

[SableSprings]

Sorry not to get back to you sooner, but yes, what you have is the correct material to make the high-temp home brew mortar discussed in the forum. Hydrated lime can be used in both building and gardening...the building applications require a finer ground product (which makes it very reactive) and if you use the builders' finely ground hydrated lime as a gardening soil additive you use much less (also because it is more reactive to water ).

It is a good idea to mix your dry home brew materials together before you add water...kinda like making muffins--mix the dry ingredients first and then add the wet . Hydrated lime is definitely a skin irritant and you will want to wear protective gloves, eye protection and a dust mask when using the finely ground product. The material that's normally used as a gardening soil additive is in pellet form and not nearly as reactive (because of the pellet size and some added ingredients) and an application to the soil lasts much longer.

Hope that helps clear this muddle up a bit...

[llamabucket]

So I read the back of the bag and here's what it says:

"To use as lime wash, mix 6kg with water to a creamy consistency and allow to stand 10 minutes before using. A small capful of dissolved salt added to this mixture will improve adhesion considerably. For sweetening lawn and garden soil, apply a week before or after fertilizer has been added. The recommended dosage is 24 sq. m per 6kg bag"

So I'm confused. This is both for building and garden work? It says it's an irritant and it says it's hydrated lime!

I'm glad you found the stuff at the potter store. It looks to me like the Rona hydrated lime is the correct stuff. I also looked up a couple resources and found this helpful bit about Dolomite and hydrated lime.

"Builders Lime is NOT the same as Dolomite or Garden Lime and is therefore not safe for the garden. Builders lime is hydrated lime, made from limestone, from 'burnt lime' which is heated to make it more concentrated and then hydrated with water, very reactive and likely to cause root burn if you are not careful. Dolomite and Garden Lime are safe to the touch."

Did you happen to go look at the bag in Rona? I suspect in the list of uses on the back it would give you some "confirming" info...but hydrated lime is definitely what you need for the mortar. It would be good if you could contact someone in construction that was familiar with the local products and brick/mortar work. At least you'd be able to get some "professional" confirmation. Sounds like you're making progress anyway!

[llamabucket]

Thank you for that info! So, I actually bought this stuff from Rona and took a look all over the bag for any information, but unfortunately there's no hints as to what it exactly is. It only says "for household, garden and commercial use"...which is pretty broad lol!

I DID buy it from a home improvement/renovation place so I'm assuming it's used for building...but again I'm just guessing

As for the dolomite stuff, it was actually suggested by the pottery shop guy. They sell products to repair and build kilns! So I'm fairly certain it would also be used for stuff like this....but I'd love to know for sure.

[SableSprings]

I'm glad you found the stuff at the potter store. It looks to me like the Rona hydrated lime is the correct stuff. I also looked up a couple resources and found this helpful bit about Dolomite and hydrated lime.

"Builders Lime is NOT the same as Dolomite or Garden Lime and is therefore not safe for the garden. Builders lime is hydrated lime, made from limestone, from 'burnt lime' which is heated to make it more concentrated and then hydrated with water, very reactive and likely to cause root burn if you are not careful. Dolomite and Garden Lime are safe to the touch."

Did you happen to go look at the bag in Rona? I suspect in the list of uses on the back it would give you some "confirming" info...but hydrated lime is definitely what you need for the mortar. It would be good if you could contact someone in construction that was familiar with the local products and brick/mortar work. At least you'd be able to get some "professional" confirmation. Sounds like you're making progress anyway!

[llamabucket]

Hey Mike! Update
So you were right! I found all what I needed at a local potter store, yay! However, hydrated lime is impossible to find. After days of searching, I finally picked this up from a nearby store:

http://www.rona.ca/en/hydrated-lime

Is that what I need? I'm reading about "Type S" lime, but this doesn't say anything about being any kind of type? Another thing the pottery guy told me is that I could buy Dolomite from him. He said it's perfectly fine to use as well...but since I see no mention of dolomite around here, I was afraid it would be wrong to buy?

[SableSprings]

Check with a business that sells concrete and paving products. They are normally oriented to builders not home diy'ers. One problem I can solve for you is that you need to be looking for hydrated lime NOT dehydrated lime. Hydrated lime is commonly sold in places like Home Depot as Type S Hydrated Mason Lime. Fireclay is something you should be able to find at a place that has supplies for making pottery. I suspect they will also have fine sand...doesn't have to be silica sand, just fine (and not builders sand). From everything I've read, working with calcium aluminate is not for us casual builders as it sets extremely quickly.

Stick with the 3 parts fine sand, 1 part Portland cement (not ready-mix concrete!), 1 part hydrated lime, and 1 part fireclay.

Did you have a chance to look at the barrel vault build link in my post #16 above...it seems to address a lot of issues similar to what you're planning.

[llamabucket]

Mike, thanks so much again, I really appreciate all your help! Now on to continuing my oven!
One more thing, I've been googling and calling all my local hardware stores and I'm having an incredibly hard time finding dehydrated lime, fireclay and let along calcium aluminate or silica sand. Where does everyone buy this stuff?

[SableSprings]

Here's another build for a barrel vault that you might find interesting...

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/getting-started/19482-nw-ohio-build-opinions-welcome

Also, thinking ahead, you are going to need some support to set the red brick barrel facade in place. I used metal lath (for stucco work) but think that it would have been better to use hardware cloth which is a stiffer wire and would have been a bit more stable/supportive as I laid my half bricks into position...

A vent has been applied in lots of builds to help moisture escape from the oven and insulation...also a good idea and something to consider.

[SableSprings]

RE: not attaching the dome to the hearth. There is enough movement (expansion) during heating that the vault will move/expand enough to break any mortar bond you apply at 90 degree joints...the weight will keep it in place just fine and it will settle back into position as it cools back to air temps. That's the beauty of the arch design...the final piece (keystone) in a dome or arch settles the structure and makes it essentially a single strong unit of support. Basically, your styrofoam is important until you add the last piece in each vault row...at that point the arch needs no more support at that row, the bricks are now self supporting.

The mortar and design of the vault arch will make for a pretty solid structure. As I noted before, many people add some buttressing to offset the outside push but a smaller structure as you are creating is pretty stable. I'd just be putting in a wider base or some side support in the middle side to keep movement to a minimum 'cause I over-engineer and I'm not an engineer Personally, I'd be adding a ring of perlcrete 3"-4" high around the base of the vault to provide some of this support. It also would be a good way to establish the distance to the outer facade bricks.

I think your interlocking of the barrel vault bricks will indeed increase the structure's stability. Also, when you build the outside facade you can and should mortar the back bricks to the back arch to help contain the structure. There won't be the expansion issues on the other side of 2" of insulation.

When you build your front entry, it should be buttressed and/or wide at the base. Connected with your barrel vault, this front entry will help contain the vault structure, especially if you carry the interlock out into the entry and chimney area.

Again, I hope this is helping answer your questions...

[llamabucket]

I forgot to add, thank you for the form suggestion! So the way we came up with doing it is the following way. I bought 2" thick styrofoam which we cut into the inner dome shape. We'll cut a whole bunch of these that will run densely through the whole barrel vault. I did a test and it holds the bricks up perfectly! Having many of these side by side will allow us to keep them in place while the mortar cures. I'm also planning on interlocking each arch with the one next to it by offsetting the bricks. It'll be a little trickier but I think it'll help with the stability of the whole thing?

[llamabucket]

Thanks so much for the prompt reply! Oh thank goodness that's workable! I thought it was, but I guess I needed a little confirmation from someone who's gone through this process already just to be sure
I'm surprised about not attaching the dome to the hearth?! I know the dome will be super heavy and surrounded by other things, but that seems like something could go wrong?

Another thing that's worrying me a little bit is the fact that there will be this "thin" firebrick dome free standing inside, then insulation and then another freestanding red brick dome on the outside. Do you think that the structure will be solid enough?

So yeah, I think I'll be avoiding using this creamy fire mortar and just make my own. I'll need a lot of it to fill the "V" shapes on the outside of the firebricks so I might as well save some money and make it thicker all together. I hear soaking the firebricks is necessary so they stick to the fire mortar better?

Oh and as for grinding the bricks, I understand exactly what you're suggesting! I'll test it out on a brick to see how doable this is with my diamond blade, but I suspect it may be a little hard to get the angles perfect with my handheld angle grinder :P

[SableSprings]

Pictures came through just fine that time, thanks!

That looks pretty workable to me. Remember that making a form for the inside arch will make putting this together a lot easier. Also if you make the form so you can shim it up into place, do your row of bricks, pull the shims to get enough space to pull the support form forward for the next row it will go pretty quickly. If you can grind along each side of the brick just a little, you'll get more contact with the next (upper brick) and you'll need less mortar. You can look at your layout photo and hopefully "see" what I mean to increase the brick to brick contact and it will ultimately lower the whole structure a little as well.

Don't mortar the back wall to the arch/barrel as things are going to need room to move during the firing. If you do mortar it, do so lightly as it will break free down the road no matter what you do. (Also don't mortar the barrel bricks to the hearth...they need to expand/contract as well. Just sitting on the hearth works just fine.)

[llamabucket]

Let's try this again, here are the photos:

[SableSprings]

I can't see your pictures in the above post. Did you use the little camera icon, click upload, select your pictures, and then upload them?

I wouldn't make lengthwise cuts on each brick...it doesn't leave you much contact area for the adjacent bricks. You might just have to find some more used firebricks, source some new ones, or go less than 32" deep.

[llamabucket]

So yeah, I agree that a semi circle arch would be best. Based on how many bricks we have available, here is the ideal layout. I'd love to lay the bricks on their 4" side, but I simply don't have enough. I am hoping that this will hold properly! Especially since I plan on interlocking each arch with the next one by offsetting the bricks nicely. I'd love to cut the bricks lengthwise but I think it would be unbelievably hard and time consuming so I'm trying to do it the way they are. This dome height below is 14.5"

As for the mortar, yeah...it's very expensive in this premixed form And since I don't have super thin gaps, I'm concerned that not only will I use a TON of the stuff but the watery consistency won't be good enough to hold it together. It was fine for the floor, but I think I'll either make a thicker home made one or buy some dry refractory mortar and create the thick consistency myself. That would be best.

Thank you for the help! I really appreciate it If you can point out any issues from the above photos please let me know!