Using Refractory Mortar to skin Vermicrete dome

[SableSprings]

Be careful about loading wood to dry in the oven after cookouts. Several folks have lost their metal faced wood doors and the possibility of a backdraft (reducing) fire is potentially dangerous to you. Your oven is going to stay pretty hot for several days after a pizza party. I bake bread on Fridays with the oven ending temps at 450F-500F but don't put any wood in for "extra drying" until Sunday when I'm between 200F-250F. That works great and I just don't see a need to rush it and have a problem with a spontaneous fire . Definitely don't put your wood in without leaving the door open significantly...after all you want to have any moisture you've driven off to exit the chamber. I'm with you as I'd not feel comfortable loading up the oven with wood to dry when I'm not going to be able to monitor it occasionally (instead of catching ZZZZ's ). Just my two cents based on my experiences over the last 9 years operating the Dragonfly Den WFO (and our west coast fire situation this year especially).

[desmodici]

Thanks. That’s great advice. To your point below I’ve been a little paranoid to do that as I usually go to sleep shortly after our cookouts, so don’t want to risk logs catching fire. Lol

Given the dry climate here in SoCal for the most part the wood is very dry and burns clean. When I get logs that I feel may have some moisture I put them on my built in gas grill for a about 10 mins to dry them out (built in by previous owner and it’s the only use I have for it as I do all my grilling on a PK grill with charcoal). Thankfully the smoke concerns haven’t played out and it’s been burning very clean and smokeless after the first 10 to 15 mins, and within that time it’s minimal smoke.

You're probably already doing this, but the best advice I can offer for that is after you cook and the oven has cooled a bit, load your next burn of wood into the oven and put the door on it. Let the residual heat from your recent cook drive the moisture out of the wood. Your next fire can be lit with a single match and it'll be rip-roaring within a couple of minutes. You won't have that smokey smolder that occurs when using wood with an ambient moisture content.

Don't load it when the oven is too hot or you'll open the door to find a pile of hardwood charcoal. lol

[desmodici]

Latest pics. Black soot around the bricks due to burning a couple logs of very sappy pine that were in the last batch of firewood that I bought.

[mongota]

Something that...wouldn't put out too much smoke given the close proximity of neighbors...

You're probably already doing this, but the best advice I can offer for that is after you cook and the oven has cooled a bit, load your next burn of wood into the oven and put the door on it. Let the residual heat from your recent cook drive the moisture out of the wood. Your next fire can be lit with a single match and it'll be rip-roaring within a couple of minutes. You won't have that smokey smolder that occurs when using wood with an ambient moisture content.

Don't load it when the oven is too hot or you'll open the door to find a pile of hardwood charcoal. lol

[desmodici]

well said David, I approached the build with that in mind, a compromise between "the perfect oven" and reality of my restrictions and requirements. Given HOA restrictions, space in my yard, close neighbors etc., I wasn't able to pull off my dream build of a conventional brick oven. I also wanted to do something with minimal effort/cost to test the waters and ensure this is something I would use frequently, wouldn't put out too much smoke given the close proximity of neighbors, etc. E.g. I was initially going to go with cement base but switched to wood after I realized 1) how many bags of cement i would have to haul/mix and 2) how much effort would be required if I had to tear it down for some reason. I'm very happy I went the wood route as it simplified things greatly. Entire build which included a lot of drying time took less than 3 weeks of intermittent work, mostly on the weekends.

So far my major concern of smoke bothering the neighbors is not an issue. It produces minimal smoke while getting the first few logs going but once it hits 300 internal temp its completely smokeless.

I will definitely report back frequently and if I experience any issues. I use it about once per week so will get some good testing on the design etc.

[david s]

Nice job. I’d be most interested in how your oven will stand the test of time. Can you report back in a years time? The two big drawbacks of a vermicrete dome are lack of strength and thermal mass. However, just as with boat design it’s all a matter of compromises, what you gain on the swing you lose on the roundabout.

[desmodici]

More build pics

[desmodici]

A few more of the build along the way

[desmodici]

That’s correct. It’s a Duratech double walled 6 inch diameter 24 lencgth pipe with a chimney cap, both bought from forno bravo. Love the look of it as well and functions flawlessly. I’ll take a few more pics tomorrow and update the thread.

[mongota]

Looks GREAT desmodici ! Where did you get that smokestack? I like it!

Looks like a Dura-tech Stainless cap (8DT-VC) and pipe.

[bentedesco]

Looks GREAT desmodici ! Where did you get that smokestack? I like it!

[desmodici]

[desmodici]

Just wanted to update everyone on results. Below was the process I used to build my oven, which Ive been using all summer long with great results:

- Vermicrete dome over exercise ball, roughly 4 inches (allowed to dry for a week with wet blankets)
- Flipped it over them applied a coat of castable refractory cement to the inside of the dome (approximately 1 inch thick)
- Placed it on table built with wood, topped with stone pavers, then insulation, then firebrick (it was heavy to carry and flip, but not too bad)
- Coated the outside of the dome with refractory mortar, covering the firebrick and insulating base
- Applied 2 inches of insulation with chicken wire
- Coated with scratch and base coat of stucco
- Last Step: will coat with final layer of acrylic stucco

As mentioned, I've used it now about 12 times and its functioned flawlessly. It takes about 5 medium logs and 45 mins to get up to temp then burns
very efficiently. I'll post additional images

[desmodici]

Thanks for the feedback and insights. Given feedback that thin layer will likely fail I plan on using a mold to do a refractory casing (mixed with SS needles) that's thicker. Will report back on how it goes

[david s]

Apart from a resulting thin layer being likely to fail the substrate it is applied to, in this case vermicrete, needs to be a bit moist or water in the applied layer will be sucked out leaving insufficient for the hydration process. Also if the substrate is too wet it will interfere with achieving a good bond. So not dry, but not too wet. Give it a try we’d be interested to hear how you go.