Thoughts on this oven build...

[almondsurf]

Re: Thoughts on this oven build...

David s: thanks for your reply. I am now researching the Melt Extract Stainless Steel Fibers. Do you have experience with these? This might sound silly, but I wonder if they would poke you while working with the mix, after all, most surgical needles are made with similar material. Are they pliable? Most likely I will be using polypropylene fibers, but as you said, they don't add strength.
Do you guys think it would be better to cast the oven in parts (for the refractory portion) then put it together (like this one)? I wondered if that would help with the heat expansion issue.

[david s]

Re: Thoughts on this oven build...

I love this forum... You guys are great. I really appreciate the replies. I am in the process of reading through Mikku and Iron Pony's threads. Good tips there, thanks.

Wotavidone: I have read through all of the "Brickless Oven on a Shoestring" thread before. Now that you bring it up... I'm going to read through it again. He uses a lot of rebar, which I don't plan to use so I hope mine will work the same. Sounds like his turned out well...

Tractor: thanks for the "homebrew" mix reference. I never thought about the polypropylene fibers, but it makes sense as long as I don't have that stuff dripping on my pizza while they cook. Do you know how much they add or how long the strands are? I'm assuming they're just mixed in with the concrete mix?

The polypropylene fibres will not add any strength to your castings. They are good to increase compression strength but lousy for tensile strength. At 160 C they melt anyway and this is where their addition is a good thing so you are left with a network of tiny "pipes" that some steam can escape through. The fibres I use are around 15 mm long and thinner than human hair. You need to mix your brew for about double the normal time so that they disperse in the mix properly. They give your castable some protection against steam explosions. Proprietary castables have them premixed into the brew. Add about half a handful for every 10 L of dry mix.The extremely low volume they occupy will not change the density of the resultant mix.
If you want to increase the strength of the castable then use stainless steel needles (melt extract fibres) as well.

[almondsurf]

Re: Thoughts on this oven build...

I love this forum... You guys are great. I really appreciate the replies. I am in the process of reading through Mikku and Iron Pony's threads. Good tips there, thanks.

Wotavidone: I have read through all of the "Brickless Oven on a Shoestring" thread before. Now that you bring it up... I'm going to read through it again. He uses a lot of rebar, which I don't plan to use so I hope mine will work the same. Sounds like his turned out well...

Tractor: thanks for the "homebrew" mix reference. I never thought about the polypropylene fibers, but it makes sense as long as I don't have that stuff dripping on my pizza while they cook. Do you know how much they add or how long the strands are? I'm assuming they're just mixed in with the concrete mix?

[Tractor]

Re: Thoughts on this oven build...

Hey almond surf

I'm looking to cast my oven as well so I've been doing a lot of reading on here and the two major things I consistently read about people casting their ovens is a 3-1-1-1 mix works. That's 3 sand 1 lime 1 Portland cement and 1 fire clay

The other thing I keep seeing is that some people add polypropylene fibres (an old rope all separated out) to their mix, that means when you do the first firings the fibres burn away leaving tiny tunnels for the moisture to escape preventing steam build up and cracking but it also means that if a crack does start it'll stop as soon as it hits one of these micro tunnels

Trac

[UtahBeehiver]

Re: Thoughts on this oven build...

As I mentioned before, you need to look at Mikku or Iron Pony's thread, their builds were cast and you can get more relative info there if cast is the way you want to go. Nothing wrong with cast, each to their own.

[wotavidone]

Re: Thoughts on this oven build...

Mixes made with lime, clay and portland cement are not, strictly speaking, refractory. So your friend is correct, CAC is probably better, it is much more heat tolerant, but it does have its little foibles apparently - sets almost too quickly, and doesn't work very well if you don't use exactly the right amount of water as specified. So they say, I've never used it.
Don't add lime is the usual advice.

Having said that, the 3 sand, 1 clay, 1 lime, 1cement home brew mortar used commonly used on the forum has been used to mould a dome before. see "Brickless Oven on a Shoestring".

[almondsurf]

Re: Thoughts on this oven build...

Yeah, I have thought about the cracking being an issue. I was just thinking... When ever I go to any pizza house that has a WFO, it is always a solid concrete oven. Even the ovens that Forno Bravo sell are solid concrete. I just assume that my cast would have to be pretty darn good. Forno Bravo's look amazing, but of course 'that's what they do.'
I think I'd like mine to be the size of their Casa2G80 32.
Today I talked with a friend who is a salesman for a major international cement manufacturer. He said if I am going to cast the dome, I need to use "Calcium Aluminate cement" to do so. He said it works better than Fire Clay. Maybe that is subjective? Any thoughts on that? What kind of mortar did you guys use?

Thank you all for your help. Your feedback is/has been very much appreciated!

[jeeppiper]

Re: Thoughts on this oven build...

I don't really have any experience with this, but I just think the brick/mortar dome would be much stronger than a one-piece cast-in-place dome. I can only imagine the thermal cycling would create tremendous stresses in the dome causing much more cracking in order to relieve the stress. Once a crack starts, it will keep going (i.e. crack-propagation).

With a brick-mortar dome, I would think it could handle the thermal expansion and contraction better and be immune to crack propagation.

As far as cost goes....I guess the cast dome might be cheaper.

Building the dome is fairly easy. I created a hemispherical form using 1" thick Styrofoam. This allowed the bricks to be supported. Other people use sand. Many folks use "The Indispensable Tool" (which I wished I had used). My dome is not the prettiest, but is works just fine. Many oven builders pride themselves in shaping and tapering each brick and using as little mortar as possible. I just split my bricks in half with a brick splitter (no taper) and slopped them all together with mortar.

[almondsurf]

Re: Thoughts on this oven build...

Thanks for the feedback Warrior and Jeepiper. You guys make some good points. I have laid a brick or two in my life, but making a dome seems a lot tougher. I have read a lot through this forum and several others. When I saw the referenced build I thought, "dome of sand, wrap with plastic, lay on the morter... easy enough. I will have to lay on the insulation layer (vcrete/pumice/concrete mix) that same way, regardless of how I build the refractory dome.
Do you guys think that the proposed method would be any cheaper/ less expensive to build?

[jeeppiper]

Re: Thoughts on this oven build...

I agree with Boerwarrior. I never laid bricks before and thought building a wfo would be fun. It is really difficult to screw it up. Casting a dome seems much more challenging and much less forgiving than laying brick.

[boerwarrior]

Re: Thoughts on this oven build...

almond

I also had never laid a brick before I started this project... and now there are over 1,000 bricks in my oven and surrounding structure!

So don't let that scare you off. It's not as hard as it looks and there are plenty of people on this site who love giving advice!

Honestly, as a beginner I found the idea of a cast refractory dome way more intimidating than bricks. I have no experience with refractory but it seems like you really only have once chance to get it right. With Bricks you lay them one at a time and it's easy enough to knock a few out and re-lay them. Just my $0.02-

[UtahBeehiver]

Re: Thoughts on this oven build...

I never laid a brick until this project there are many others on this forum who are novice bricklayers as well. Just takes patience.

[almondsurf]

Re: Thoughts on this oven build...

UtahBeehiver... Thank you for the feedback and taking the time to read the link (and my lengthy thread question ) I have looked through your oven thread. You have some serious skill with brick laying. I'm not so fortunate, this is why I wanted to do the cast WFO. I assume it will be less expensive and turn out to be quite nice if I take my time. I plan to build a relatively small oven (enough to cook 2 pies at a time); this way it will heat up quick and consume less wood, which is hard to come by down here.
I plan to stucco the outside with a waterproofing agent in the stucco as well as coated on the outside.

Any tips from the community would help. I cant wait to get this project underway (my wife too... she's tired of hearing about it )

[UtahBeehiver]

Re: Thoughts on this oven build...

I read through the link you provided and it is not a brick dome style which is what the majority of the ovens on this link are. But there are a few cast ovens that have been done and they fire at the same temps as the brick. Mikku, IronPony are just two I can remember. I see the proposed insulation is a vcrete/pumice/concrete mix which is fine it just takes more inches to equal materials such as CaSi board or blanket. Being in St. George you will not normally get the freezing cycles we see farther north so a good stucco with a polymer additive should work as well. I can't comment on the refractory portion of the build since I did brick. Good luck

[almondsurf]

Re: Thoughts on this oven build...

My plan is to build this type of an oven in 2 months (after I finnish a few other projects). Wondering if anyone has any answers to the questions I posted. I should be purchasing materials in a few weeks. I'll post pictures along the way.