Longmont, CO new WFO build - casted over sand

[cnegrelli]

Enclosure is only lacking some support for cement board around chimney, which I will weld today. Then the enclosure needs to be put in it's final resting spot on the stand, and fastened down well.

[cnegrelli]

I posted this on an older thread having to do with Stucco, but will ask here as well:

What is the preferred underlayment for Stucco? Cement board? Hardiebacker?

I've read with some confusion the right way to Stucco over hardiebacker or Durock.

tape and mud all joints, roof felt all surfaces, lathe and three coat stucco method?
Can I use some Red Guard on the top surface, which is flat? (I will have a vent). Will the heat be too much, despite the 6" of blanket and filling the enclosure up with Perlite or Vermiculite?

[jonv]

Don't know about the stucco but can answer your last question - with 6" of blanket I think it should only just be warm to the touch. I doubt if you'd feel anything much on the outside of your enclosure - my igloo gets much hotter from the sun than the fire and I've only got 4" of blanket (128kg/m3) - doesn't get hot even with the dome inside over 600C.

[cnegrelli]

Anyone know how to procure or form an arched corner bead for stucco work around the chimney opening, where my chimney opening is thru a stucco (or tiled) surface?

[UtahBeehiver]

I have seen arched bead for stucco but you probably won't find a a big box store but more of a stucco distributor. For a small arch you may be able to slot and bend a standard stucco bead like shown in the attached factory arch bead.

[cnegrelli]

I was looking for that exact product, but don't see a way to buy it. I looked at Home Depot and they have something similar for drywall (vinyl). It can't get close to the radius I would need, but by cutting more slots, perhaps? I have not seen actual stucco bead up close but they seem very similar? I will study some more, but any discussion is helpful.

[UtahBeehiver]

Like I mention you probably need to go to a dealer that specializes in stucco materials.

[cnegrelli]

It occurs to me that my dilemma in stucco up to the chimney is really no different than the dome builds, with stucco finishes. It would seem that I could use some material with tape to cover my SS chimney, and create a small gap and thus stucco up to that? It's a double-walled insulated Duratech from the FB store, and doesn't really get hot on the outside. I know I studied DavidS's vent/Storm Collar hybrid solution, but I don't really know how he cozies the stucco around the chimney pipe.

[david s]

I'll pm you

[cnegrelli]

Do most people finish the inside storage area of their ovens? I plan to use mine for wood storage. I did some searches and failed to find much. I plan to have a stone veneer external walls of the stand.

[Gulf]

I do not use mine for wood storage. But, I did patch the dry stacked joints witn normal mortar and then seal mine with Drylok.

[cnegrelli]

Got the oven up in Temp today and also discovered the "wet issue". I have been working on my enclosure a bit and firing the oven a bit this week. Still seemed to be wet down low on the walls. Discovered that the concrete hearth was wet around the foamglas that supports the CaSi and then Firebrick. Here's what I think has been happening:

1. cast dome over sand and left wet sand inside dome for a week, while misting heavily the top of dome and keeping tarped. Water definitely dripped off dome and would hit CaSi. Because Im' doing an enclosure the firebrick floor, and the insulation under it extended beyond dome, so water collected on it. I believe the CaSil got pretty saturated on the edges.

2. after digging out the sand (and David telling me I didn't have to keep it wet like that) I let it dry out a few days, but then re-soaked the inside so that I could patch the dome in a couple places where I had voids. This likely contributed as well to more moisture collecting on the CaSi, thru the cracks in the Firebrick.

I seem to have most of the moisture out, but I'm still not full-go on the fires. Here's a pic around the FoamGlas.

[cnegrelli]

Concluded attaching Hardieboard to the enclosure. Anyone know how forgiving the taped joints will be with Stucco applied? Some of my joints are perfect, others I have a bit of a joint mismatch (geometry is hard). Trying to determine if I can tape as is or if I should use some "fat mud" as tilers do to plumb up walls before application. My thought is that the stucco can cover it all up with "floating".

Inputs?

Also, because I used heavy gauge steel framing, the hardiebacker fasteners wouldn't penetrate without pre-drilling. That was a blind PITA. I ended up using some TEK self-boring screws that worked well. They do stick out a bit, will that be ok for stucco?

[david s]

I like to add another coat over the cement stucco which covers any troweling marks and also fills cracks. I use a flexible acrylic product. A 100% acrylic render works well. I find it's easiest to apply by watering it down 20% then you can brush it on. Because it contains sand you get a high build coat.

[cnegrelli]

That's my plan.
I plan to tape/thinset the hardieboard then stucco.
Do you apply a stucco mesh and then a 2-step stucco ? Then acrylic?