Longmont, CO new WFO build - casted over sand

[cnegrelli]

You may not need to level the FoamGlas/CaSi if your hearth was poured flat. You will "not" see significant temperatures on the bottom side of 4" of insulation. If you need to so some leveling, a damp sand mix grooved with a notched trowel will suffice.

Thanks Russell. I laid down the FoamGlas last night (and one piece of CaSi) to get a feel for it. My Hearth has a low spot near the back that pools water slightly, so I need to level a bit. I will also need to cut off a few corners of each of the materials above so they don't extend to my enclosure walls. What did you find was the best way to cut each? I noticed you mentioned a jigsaw (blade type) and scoring the FoamGlas with a shard (I assume a shard of FoamGlas)?

[UtahBeehiver]

You may not need to level the FoamGlas/CaSi if your hearth was poured flat. You will "not" see significant temperatures on the bottom side of 4" of insulation. If you need to so some leveling, a damp sand mix grooved with a notched trowel will suffice.

[cnegrelli]

In order to level out the FoamGlas and Insulation board, I've seen a 50/50 sand mix with fireclay used. Is the fireclay required? Is the thought that it would get hot? Since I'm doing a casted oven, I wasn't going to bother with homebrew mortar and thus no fireclay has been sought out. I do have a bag of high temp mortar for patching, etc. Probably have plenty, but I have no idea how much I'll need for that portion.

What is the thoughts on the proper way to level out the 4" of insulation board I have for under the firebrick floor?

[cnegrelli]

I think you will have to recalculate. The volume of a sphere is 4/3 Pi r cubed (not squared)

The mistake was in my verbage above, not in my calculation! I had it cubed. Does that sound like I'm in the ballpark?

[david s]

I think you will have to recalculate. The volume of a sphere is 4/3 Pi r cubed (not squared)

[cnegrelli]

Using some handy tips I've noted on various threads via david s I've calculated I will need 3 55lb bags of refractory. 32" diameter is a 16" radius, 2" thickness. Using volume = 4/3 Pi times Radius squared, gives a inner volume. Subtracting that from the outer volume and cutting in half to get half a dome, yields about 2014 cubic inches. Which is about 33 cubic liters. Using a 85% factor, I bump that to 39 cubic liters. Somewhere, David posted 16.37 liters per 55 lb. bag. So that works out to 2.4 bags. Will order 3. For those curious, these are $46 per bag at my local refractory supplier. Prices vary widely.

The product I plan on is CastMax 28, discussed previously in this thread.

Edit: per below, the calculation for volume is cubed, not squared. volume = 4/3 Pi times Radius cubed.

[UtahBeehiver]

I recalled that you said you were doing an enclosure so there is no need to do "round" cuts and precisely fit the floot, just make sure all your floor bricks are on the CaSi/FoamGlas insulation. If they go proud in length, no issue, they will no be seen once the enclosure is up.

[cnegrelli]

Removed the forms from my stand today (finishing the wood storage area removal in the dark) but feel it came out pretty good. I don't see any obvious problems such as voids or non-straight edges.

The 10" Wet Tile Saw I planned to borrow to just cut my floor bricks is unavailable because the owner is in Africa! I will only be cutting the floor bricks, so it would seem that I don't need to be doing Taper cuts. Is a 7" saw enough for the "round" cuts I will be doing? Prefer to keep it wet, as I am pretty sensitive to dust/particulates.

[cnegrelli]

david s - Appreciate all the hand holding. I am not 100% sure I follow your terminology of "Mould door plate".
I assume you mean a model of the opening size/shape that would be place into the hemisphere shape such that the front opening is formed. And I can trowel up against it to create the "inner arch" essentially, with a flat vertical edge. Or I could just do wood forms?

Also unclear on your mention of plastic pipe or sheet metal, etc....

Here's a pic of the shape of gallery I plan (assuming that is the correct term as well). I plan to use an anchor plate and duravent chimney system, and create the flue with the castable up to the flat part that the anchor plate would attach to. Bought the anchor plate in fact today from our host. Would like to maximize the funnel shape to help pull the smoke up as I've read.

Does anyone know where this picture came from? Wife found it somewhere....

[david s]

When you have completed the dome casting, remove the mould door plate, but not the sand behind it. You can then form more sand in front of the oven as a mould for the flue gallery. You will need anothermould plate for the front of the flue gallery but won't need one for the back.Don't forget to cover the sand mould with strips of wet newspaper so you get a nice inner surface. Forget the manufacturers recommendations on water addition and just mix in enough to make it nicely workable. Too much and the mixture will slump, too little and you'll get more voids. Don't go more than 2% of dry weight of castable for the ss needles or you'll have trouble getting a nice workable mix. Don't mix up more than 1/2 bag of castable at a time as the stuff goes off really fast. Chilled water in hot weather will give you more working time.

use a piece of plastic pipe or bend some sheet metal for both the inner and outer bits at the top of the flue gallery.

[cnegrelli]

You will also need to make another front mould plate for the flue gallery mould.

I am envisioning this above as three mould plates. One when doing the dome. Then 2 for the flue gallery (back and front)?

I plan to use an anchor plate to attach a SS chimney. Are you saying I could use sand to shape the flue? Having some 3D visualization issues here!

[david s]

Once you've cast the dome over the sand mould, and it has set after a few days, remove the mould door plate and build another sand mould in front of the door. Make it slightly wider and taller to create the door rebate. If you want to make the expansion joint there, place some cardboard there that can be removed after it sets. You will also need to make another front mould plate for the flue gallery mould.

[cnegrelli]

It's up to a 32" oven now. So 36" diameter outer shell.

Yes, the tradeoff given the slab existed, was make a bigger oven which I have resisted the urge, mostly because of things I've read from you! I don't see the need functionally to go much bigger. I do now plan to build an enclosure, but it's minimalist, leaving room for 2 par stools on the right side and room to work on both sides.

Here's a picture of the octagon shape (in 3D that I plan to build mostly because my wife likes it and she has design say, while I retain engineering say-so!

I'm on vacation at the moment and starting to plan the casting of the flue gallery. Really struggling with how best to do that with simple molds. I plan to use a sand form for the dome, but it would seem inadequate for the flue gallery - so any suggestions welcome. Looking ot maximize function here, as it will be enclosed ultimately.

Also plan is currently for a thermal break just outside dome area (Inner arch). This will be the transition from the dome to the gallery, if I'm getting my terms correct. Comments?

[david s]

You have a huge base for a 28-30" oven, given that most cast ovens of that size only have a 2" thick inner shell..Will all the area outside the oven be for prep?

[asudavew]

Sounds like a fun oven to build. More pics!