Cinder and basalt in oven construction

[Kalapana100]

Aloha from the Big Island of Hawaii.

I am interested in the pompeii oven and was wondering if anyone had any experience in using either volcanic cinder in place of pearlite or vermiculite, and/or basalt ("blue stone") in place of fire brick.

I live in hawaii, and brick is harder to get, and expensive, but basalt can be free, and cinder is $20 US a pickup load.

Thanks,

Kevin

[dmun]

Re: Cinder and basalt in oven construction

Volcanic pumice is a good insulator, you use it exactly like vermiculite, either in loose fill or as a concrete aggregate.

Basalt, I don't know about. It's an igneous rock like granite, and therefore really hard to cut. I don't know about it's thermal properties. I know granite chips away (flame finished) when intense heat is applied to the surface.

Around here, on the US east coast, "blue stone" is a form of slate. That you don't want. I know Kalapana isn't talking about that, but I thought I'd throw it in for anyone else reading the thread

[gjbingham]

Re: Cinder and basalt in oven construction

I love dmun's posts. He knows tons about everything. I just checked out his homepage. Cool clocks!

Hawaii is really expensive, but I think if you want to do it right, I'd spend the money on the firebrick at a minimum. You can probably work around a lot of the other materials, but if the oven doesn't cook the way you want, then it may be a let down.

James recommends building it with normal bricks (rather than not building at all) if money is really an issue. If you could get your hands on some cheap used bricks on Craig's List, that might be a good way to go.

[DaveHI]

Re: Cinder and basalt in oven construction

Sourcing materials in hawaii is a pig. At least you are on the BI where there are some wood stove dealers that have mortars etc.

I bought my bricks via Evergreen by Debra -- an Oahu tile/stone dealer. They shipped them in from Castaic Brick who are just north of LA. Was easy. Bad news is I paid about $750 bucks for 250 bricks. Have about 75 left over so don't be dumb like me and leave such a huge safety factor. I think the bricks were only about $1-$1.25 and the rest was shipping.

I bought underfloor insulation from FB. Shipping was brutal. Dome insulation I got elsewhere and luckily a neighbor had a way to freight it for free. I bought 6 bags of FB italian mortar. With 20/20 hindsight I'd have gone with the home made formula and just shipped in a bit of fire clay. I found the home made mud more forgiving.

Regular type N mortar mix is 1 part Portland, 1/2-1 parts lime and 3X the sum of those 2 in sand. By adding fireclay a bit more portland and lime I got the mix to about the FB recommend ratios. Seemed much more forgiving on workability. And i can't see any difference in cracking on the dome. About the first 2/3rds is FB italian mortar the the top is home made.

You should be able to get vent pipes etc from the Hilo/Volcano area stove dealers. I shipped mine in again at painful shipping cost.

really light pumice is an ok insulator. but it's nothing like the space age stuff. So unless you are willing to have a very large enclosure and a much greater thermal mass, I'd pony up for some good insulation. Now that mine is fully dried, it gets hot fast and holds heat well.

My homesick Italian friend swears we are making the best pizza on kauai now. He and I stood in the rain on NY eve getting soaked making pies. Now wer're trying to suck up the courage to try a small pig.

[DaveHI]

Re: Cinder and basalt in oven construction

and good luck cutting blue rock. that stuff is so hard it's unreal. the local Portuguese ovens here all seem to be brick, so if anyone has tried blue rock, I haven't found them.

[gjbingham]

Re: Cinder and basalt in oven construction

Wow,
That went up fast! Congrats on finishing it. Sounds like it was a pretty spendy project. Did you take any pics along the way?

[DaveHI]

Re: Cinder and basalt in oven construction

True. I think I have about $2200 in materials but I'm basically done. Shipping in a kit oven would have been more like triple that I'd guess. the cost of the dome was only about $750 for the bricks and maybe $300 in mortar.

I did take some pix but honestly if you look at paulages and camarina's efforts you've seen mine (and done with more skill). The only variations I employed were a

1) soldier course with the upper inside corner nipped off to make a combo soldier/skrew course.

2) Cut brick for the floor to fit inside the dome which is claimed to be more efficient.

3) formed a dimple in the concrete base for the isol board to fit in. Why? Seemed like a good idea at the time but it wasnt. Trapped water and kept the board soaking wet when I got a little rain. Had to dry the floor out 3 times before I got the enclosure done.

Started in Sept and finished in Dec so not really very fast but I had a bunch of pool and yard projects working as I went so I let each course cure for a couple of days under wet towels as I went.

[Archena]

Re: Cinder and basalt in oven construction

<Disclaimer: I've never built an oven or been to Hawaii>

The best way, in my (tiny) experience, to find out if something works is to try it. Since you don't wanna build a whole oven just to test a rock, why not give the basalt a test run on an open fire or barbecue grill? Use it like a pizza stone and see how well it works.

If it works well, you might consider finding a slab large enough to make up most of your oven's floor then using firebrick to fill in around the edges - it would be cheaper than all firebrick and would eliminate the need to cut basalt (y'all do know it's one of the hardest rocks there is, right? It's kinda a given that it would be a bear to cut.)

Anyway, that's my ever-so-less-than-expert suggestion.

[Dac1260]

Re: Cinder and basalt in oven construction

I completed a Portuguese Wood fire Oven in two years using mostly basalt Lava rock. I cut all the stones with a pearl diamond blade with a flush cut adapter. The blue rock cuts surprisingly easy with these blades. I used 9" x 4 1/2" X 2 1/2" fire brick for the oven floor (hearth). The basalt rock is moderately porous and has properties close to soapstone which has at least a 3 to 1 ratio over fire brick regarding heat retention properties. This rock is available here on the big island very cheap. I did have to coat the inside of the oven with refractory cement to keep the basalt bricks from chipping out. I did try using the nonporous basalt for the hearth but it started to crack and chip out after a few firings. The decision to change the floor or hearth with fire brick was necessary and has shown no signs of wear or degradation from repeated use over the last few years. The refractory cement coating (about 1/2" thick) inside the oven (walls) has held up very well too.
Dave