Longmont, CO new WFO build - casted over sand

[cnegrelli]

Was able to ream out the area for the chimney a bit, but went from sandpaper to grinder quickly..

Mounted anchor plate with high temp caulk. Put my 48" chimney on top and everyone thinks it's too tall. Hmm.
That's the engineer in my. 48" is more draw than 36". Plus I got it on Craigslist for $40. Back to the drawing board I suppose.

[david s]

If it were mine I'd be filling them. Keep the unused castable in sealed plastic buckets. I like to do this operation straight after de-moulding the casting so it's still moist. That way the patching material doesn't dry out too fast. As yours has been a week you may have to try and dampen the whole casting first, fill the voids, then keep it covered for a day or two.

Great going for a first build. You laid the floor a week ago and you've now finished the dome and gallery. It takes most brick builders months to get that far. The hard part is now done,

[cnegrelli]

You may have some voids to fill on the inside so keep the casting damp until you remove the sand. I sieve out the larger aggregate and make up some mix to a peanut butter consistency for doing this operation.

Brushed out the sand this morning and I do have a void in the top of the dome that is about a 1/4" depression, perhaps 2" in a circular shape. Is this worth opening a new bag of the castable and filling the void?
There is a 2nd void near the entry where the sand mold up against the door had shifted (previously shown). But that area is 3" thick and is cosmetic only so I will only address that if I'm addressing the other.

Opinion from david s ?

[david s]

See how you go, but I think a grinder is a bit too savage.

[cnegrelli]

Sand paper as opposed to my grinder? Do I need be that gentle?

[david s]

Removed all of the sand this morning. On first inspection, I don't see a single void. Because I didn't use newspaper, it's a bit rough, but fully functional.

I am extremely happy with the sand mold process. The gallery flue area also came out as expected. There is a small void/blemish if you will near the top of the flue on the front that would be visible so I may try to doctor that up today. But I will probably practice on something else that won't be seen to evaluate how that goes.

Scrub the inside surface with a stiff scrubbing brush. You don't want to have sand falling on your food.

[david s]

I've dry mounted the Duratech Anchor Plate to my casting. Bought this product here at Forno Bravo. https://www.fornobravo.com/store/6-d...-anchor-plate/

In my casting, I tried to form the flue opening a bit wider in diameter to accommodate the approximately 1" deep metal circular piece (6" diameter) that goes down into flue area, with some added space for potential expansion. However, I'm finding the fit to be a bit tight.

How big a concern? I don't want cracking because of expansion of metal and had hoped to have made it bigger than it actually came out.

Having cracked the casting on both the second and third ovens that I built, I was sure that the expanding ss flue pipe was the culprit. I had cast directly around the pipe, so it was super tight. If I were in your position I'd be getting some really rough sandpaper and try reaming out the inside of the casting a bit. It shouldn't take too much.

[cnegrelli]

I did not cut my 4" of hearth insulation (FoamGlas and CaSi board) to exactly fit the dome, since I plan to do an enclosure. Thus the CaSi is exposed to the elements at this point, although no rain in sight for a bit.

I plan to use a cement board product for the enclosure, over steel framing. I've done this before with my indoor fireplace remodel.
I also plan to pour concrete counter tops (polished) to raise up the level surrounding my build.

Dumb question #1: Which one comes first?
Dumb question #2: Assuming countertops first, how do you pour up to the exposed CaSi board? Is a render first applied to cover it? I think I saw UtahBeehiver do this before pouring his countertops?

Any tips, suggestions, appreciated here.

[cnegrelli]

I've dry mounted the Duratech Anchor Plate to my casting. Bought this product here at Forno Bravo. https://www.fornobravo.com/store/6-d...-anchor-plate/

In my casting, I tried to form the flue opening a bit wider in diameter to accommodate the approximately 1" deep metal circular piece (6" diameter) that goes down into flue area, with some added space for potential expansion. However, I'm finding the fit to be a bit tight.

How big a concern? I don't want cracking because of expansion of metal and had hoped to have made it bigger than it actually came out.

[cnegrelli]

Removed all of the sand this morning. On first inspection, I don't see a single void. Because I didn't use newspaper, it's a bit rough, but fully functional.

I am extremely happy with the sand mold process. The gallery flue area also came out as expected. There is a small void/blemish if you will near the top of the flue on the front that would be visible so I may try to doctor that up today. But I will probably practice on something else that won't be seen to evaluate how that goes.

[david s]

If you see visible steam you're going at it too hard, back off.

[cnegrelli]

OK - that's good news. I'll dig out the sand tomorrow and let them dry for another 48 hours and then start the curing fires slowly. The schedule for the Castmax 28 product I used has this schedule, which seems aggressive. I'll be more patient.

[david s]

Proprietary castable refractory achieves full strength in 24 hrs so prolonged damp curing is unessessary. Driving out the water is another thing, so look at your product's recommendations for first firing schedule. It will be something like 25 C / hr up to 100 C hold at this temp for a couple of hours before ramping up to 200 C at 25/ hr and the same again up to 300 C and again to 400 C. The water elimination and firing schedule is also dependant on casting thickness. Also read the thread on curing under the "oven management, firing your oven" thread.


Here's a good link for firing schedule.
http://www.darleyfirebrick.com.au/castable-use.html

[cnegrelli]

Is there a good reference for curing for castable on the site? I've read various things. Dome was cast a week ago today. I think I will dig out the sand and let it sit a week to dry out now? Then wrap in insulated blanket and start small curing fires?

[cnegrelli]

On this photo, along the top of the arch, it looks like a crack in this picture, but it's really just more like a void or where two different "layers" came together. If I recall right, I can mix up some more and do a little surface smear on there for appearances? That section will be visible even after the enclosure build.