Another Minneapolis WFO

[david s]

Impressive shelter around your kiln! I am curious about the cement mix you used, looks like 50% home brew and 50% ready-mix... Wonder what the Ready Mix was, whether it was a plaster/render mix or a tile/brick grout mix? I spent a few hours this morning just browsing timbrel arches and thin-shell vault construction on Youtube, lots of info there too.

It was a bagged cement render (poly modified). My 50% addition was a rich mix of graded sand and cement 2.5:1 with some powdered clay to improve the mix consistency and random fibre reinforcement.

[Sixto]

Impressive shelter around your kiln! I am curious about the cement mix you used, looks like 50% home brew and 50% ready-mix... Wonder what the Ready Mix was, whether it was a plaster/render mix or a tile/brick grout mix? I spent a few hours this morning just browsing timbrel arches and thin-shell vault construction on Youtube, lots of info there too.

[david s]

If you're interested in timbrel arches you might find this interesting.

https://makezine.com/2009/06/30/lost...brel-vaulting/

And my thread, starting here

https://community.fornobravo.com/for...kiln#post14564

[david s]

I don't think that would be necessary, because your gallery is so far away from the heat. You should be able to hold your hand against the inside of the gallery when the fire in the inner oven is really cranking. Raking coals into the gallery would increase temperature but not that much. You could always trowel over a 1" 5:1 vermicrete after it's finished if you think it requires it, but I don't think you'll need to.

Guastavino and Gaudi two of my favourites.

[Sixto]

I really like this solution, apart from using it as a grill area, not only does it give you far better access to the inner oven, it also provides a big volume for smoke collection. I think you may have started a trend. We could call it The Sexy Sixto Solution.

...reinforcing thin masonry arches arranged in a single skin by laying several layers (one or two) of flat rectangular tiles alternated with layers of hydraulic mortars. The effectiveness of the method was further improved by embedding composite fabrics (GFRP) between the tile "

I'm not crazy about my name (having been teased about it all through High School), but I really like the idea of reinforcing the arch with a layer of mortar and tile, and composite fibers. This reminds me of the Guastavino (sp?) vaults I learned about in Architecture School...How does insulation work into this scheme? Still apply it to the outside surface to keep temps of external surfaces relatively cool?

Thanks!

[david s]

I really like this solution, apart from using it as a grill area, not only does it give you far better access to the inner oven, it also provides a big volume for smoke collection. I think you may have started a trend. We could call it The Sexy Sixto Solution.
A couple of considerations, as the gallery semi circular arch is so big it’s thickness is proportionally relatively thin. These kind of arches being unsupported at the sides are vulnerable to outward thrust(something the Romans knew very well) Strength can be increased enormously by laying a second layer of bricks with no joints lining up. This would probably be overkill, but a concrete layer enriched with fibres of around 1” over the brick arch might do the trick. I suggest you don’t place too much weight on top of the arch like a brick chimney.

Lots of info and ideas here

https://www.sciencedirect.com/scienc...59836815005430


"A total of seventeen specimens, assembled with flat rectangular tiles and loaded at the keystone, were tested with these variables: strengthening scheme, number of arch rings and mortar type. The retrofit scheme consisted in reinforcing thin masonry arches arranged in a single skin by laying several layers (one or two) of flat rectangular tiles alternated with layers of hydraulic mortars. The effectiveness of the method was further improved by embedding composite fabrics (GFRP) between the tile "

[Sixto]

Photo Update:

The dome is closed-off, not pretty, but I think it will hold. I also realized I did not properly describe the gallery arch, so now that it is started, I will show the details, talk about why I went with an arch rather than straight sides, and talk about the possible shortcomings of this design...

The photo below is an overall view of the gallery arch form and the first few brick courses on either side. I have the form up on wood blocks and shims so I should get about 2" of clearance at removal time.



The reason why I went with an arch for the gallery rather than a straight-walled-box is simple, I'm the only one in my family that favored the straight wall design, everyone else liked the arch better. Because of this, I lost about 2" of head-height... right now the bottom of the arch keystone will be about 21.75" above the gallery floor bricks.. Building the arch is going slowly because of the detail below, every single brick oriented radially next to the outside face of the dome arch has to be cut to form around the gasket and insulation, plus they need to be tapered about 1/4" top and bottom at the inner edge to match the alignment of the main gallery courses... The main gallery arch has alternating tapered and standard brick courses, and the straight courses make the 90d turn to meet the outside of the dome arch. (the letters on the face of the form are not an accurate guide to courses)

As I may have mentioned before, the goal is to be able to use the gallery as a grill area when I'm not making pizzas or bread. The gallery dimensions are: 36" wide, x 18" deep x almost 22" tall at the center...My wife tested the fit of our paella pan, and it fits inside the wooden form, so there should be plenty of room for anything I want to grill. And this does NOT eliminate the option of having a Tuscan grill inside the dome. I can start a fire in the dome early, pull the coals out into the gallery floor and add a grate on stilts to grill.

This all came as an afterthought, when I realized I had placed the dome entrance about 27" behind the edge of the slab, and reaching-in would be tricky for me if I did not make the gallery bigger, so I could get my head under the arch. I could have made a shallower flue gallery and just deal with the reach issue, but the idea of adding a grill area to the front made sense to me.



One possible downside to this design is that the full front face of the dome arch is exposed to the air, (you can see it in the overall photo on top) and may lose too much heat through that surface... I may have to make a bigger insulated door to cover the whole 4.5" of exposed brick arch... I did back up the gasket with 1/2" ceramic fiber insulation, so at least the gallery arch bricks will not be sucking heat from the dome by conduction.

With this much separation between the dome and the flue gallery, I wonder if I need as much insulation around the flue gallery arch and transition to the stainless steel flue.. maybe just a couple of inches of perlite cement, stucco and tile?

[Sixto]

No, I've found that mixing the dry materials together first is a much better method...For a 10:1 over the dome insulating mix that has low strength, the addition of AR glass fibres does little to enhance its strength. I think they are a waste of $ in this particular mix.

Perfect, I will follow your advice, thanks again!

[david s]

David, I copied your note above to have it as a reference in my build process. Do you think that mixing the cement/clay/water first to make a slurry and then adding the slurry to the Perlite/Vermiculite/Alkaline Resistant glass fibers (and mixing it all together by hand) would be a good approach to avoid water pooling at the bottom of the bucket?

Thanks!

No, I've found that mixing the dry materials together first is a much better method. If a slurry is made first the mix tends to create balls of cement and clay which have to be broken up with the back of the spade to mix in with the lightweight aggregate. If the materials are mixed dry first and the water added slowly and progressively this problem does not occur. I've mixed up tons of this stuff by hand, do it almost daily and have found hand mixing it in a barrow dry first, with a spade is the best method so far (for me at least).

For a 10:1 over the dome insulating mix that has low strength, the addition of AR glass fibres does little to enhance its strength. I think they are a waste of $ in this particular mix.

[Sixto]

As the attached table shows the addition of cement to the mix drastically reduces insulation value. I find a 10:1 mix is about as lean as I can go and still have the stuff reasonably workable and resulting in a substrate with sufficient strength to render against. It results in a layer about as insulating as blanket. If doing an enclosure a dry mix of perlite is the best insulator and there's no problem about having to drive off the water. However, for an igloo style, with no walls to contain loose material it requires something to make it stick (cement) and water so the cement will react.
I do the whole oven in one go, to a thickness of around 35mm (one and a half inches). Any thicker and drying the inner part of the layer becomes much slower, better to do subsequent layers with a week of drying between layers.I use just hands to place the mix , always starting from the base and making a flat ledge on the top which allows you to judge the thickness as well as having a platform for the next row to sit on. Although I do it in one go I do recommend that first time vermicreters just do a row at the base about 150mm (6" high) and allow this to set for 24 hrs. This makes the next lot to build on top of far easier. Most folk swear that the mix won't work when doing it for the first time, but it does. Apart from reducing the cement as much as possible, the correct amount of water is also imperative. Too much and the water will wash yje cement off the grains leaving an inconsistent mix. To little and the mix is too dry and crumbly. As a general rule 3 litres of water to every 10 litres of vermicrete is about right, but the finer grade grains require a little more. If water pools in the bottom of your barrow wait a few minutes as the stuff absorbs the water and if this condition persists add a little more dry material in the same proportions.
I find a little powdered clay, around a handful for every 10 litres (2gallons) of vermiculite does wonders to make th mix more workable. Also I find a mix of 50/50 perlite/ vermiculite works better than either of them alone. I use a medium grade of both. I use just a flat trowel to tap the outer surface which results in a good surface when just eyeballing the profile. It is also essential to wear rubber gloves, otherwise you'll regret it the following day.

David, I copied your note above to have it as a reference in my build process. Do you think that mixing the cement/clay/water first to make a slurry and then adding the slurry to the Perlite/Vermiculite/Alkaline Resistant glass fibers (and mixing it all together by hand) would be a good approach to avoid water pooling at the bottom of the bucket?

Thanks!

[Sixto]

Before you lay the arch bricks over your wooden form, make sure you place some removable wedges under each corner of the form. This makes removal much easier and prevents potential damage to your brick arch.

Plus one of David's comment, I used 1/4" wedges on my inner arch and it was not enough to drop the form and went with 1/2" wedges on the outer arch form.

I agree and will do that when ready to start laying bricks. Thanks David and Russell !!! I used 1/4" shims for the dome arch, but it was hard to move, so I'm going thicker this time.

The tricky thing about the gallery is that it is fully outside the dome arch, and separated by oven gasket rope. It is self-supporting, and independent of the dome so the gallery and flue don't siphon heat from the oven when it is closed. This means that at the end of the gallery, there is another arch that is 9" deep and goes AROUND the dome arch. I am planning to cut grooves for the gaskets, but if I want the same number of bricks, then the mortar gap gets really narrow at the dome arch and really wide at the outer edge, so I'm not thrilled yet... I think I will need to cut the 9" bricks around the dome arch with a taper to try to keep a consistent joint width from the outer edge of the arch to the inner edge. (can you tell I'm a little sick of cutting bricks?)

Today I spent the day cutting and re-cutting 4 bricks for the dome plug... I thought it would be relatively easy, I made a cardboard template of the top and bottom of the opening, , and cut the shapes out.... Well, of course it would not fit right and I ended up whittling the thing for at least 6 hours before I was satistied with how it fit (flush at the bottom and with relatively tight gaps)

I did patch gaps on the inside of the previous course, and they seem fine now... but I'm expecting some interior cleanup after the plug is mortared and want to do that before I start laying the gallery bricks.

[Sixto]

Nice weather today, decided to clean-up the inside of the oven so far (I always clean up mortar with a sponge as I go, but there's always something I only see later)

So I found some gaps in the mortar, from what I've read this is only an aesthetic concern, since there is more mortar behind sealing the gap.
My question is IF i wanted to make it look better and tuckpoint the gaps, do the following steps look right?

• Clean the gaps throroughly
• Spray the gap with water to get the existing mortar/brick wet.
• Use a tool to compress the mortar at the gap being filled and a sponge to smooth out any edges.
• Use the same homebrew refractory... or is there some other mortar mix/recipe that adheres better to existing mortar in an oven situation?

And finally, am I risking that one of these patches may falli on top of a pizza down the road, no matter the steps above and what type of mortar I use to fill a gap???

Gap over the arch

Gaps below the dome top (center and to the left)


Thanks - Sixto - Minneapolis - Still recharging, but also planning ahead.

By the way, my arched opening is a bit too tight for me... I can fit my head and one shoulder into the dome... good thing I have long arms.

[david s]

There won’t be any flame impingement on the casting. Homebrew reinforced with AR glass fibres would be quite sufficient. Easiest if you cast it in situ. Maybe set up in position some polystyrene suitably shaped and cast over it. You’d be wasting money using castable refractory there, with the casting so far away from the flame, it won’t get particularly hot.

[Sixto]

A simpler method would be to use brick units for the sides of the gallery with a cast top piece. In this case the anchor plate has been bothered and cast into the top of the casting.
.

Ok, so I'm taking a break from working on the oven, but apparently I can't stop thinking about it. ... david s had posted the clip above on one of my early posts, and now I'm wondering if I can still do a shallow castable top like that but on a much wider and deeper gallery, like what is shown below? (instead of having a hood fabricated out of stainless steel?)



What would be the structural implications if the inside dimensions of the brick rectangle are 30" wide x 19" deep? Bottom of the castable "hood" would be 24" above the floor.
A) Are stainless needles enough reinforcement, or would I need to add a steel angle along the bottom edge of the 30" opening span?
B) Would the DIY castable recipe work in this situation, or am I better off using a pre-mixed castable refractory?
C) Would the castable simply be grouted to the bricks below? or should it be cast around the bricks with enough material to maintain dimensional stability over time, and keep the top from shifting off the walls?

I would still slope the top, and tile over the whole thing to tie-into the look of the oven and provide some added weather protection.

Thanks! - Sixto.

[UtahBeehiver]

Take a deep breath, this is point where many builders start to get impatient, hurry things along, make errors or accept work they normally would not. You a getting close to closing the dome. gravity slows down the work as well as tedious small cuts. These ovens are labors of love, so take a step back and chill.