Kaolin clay as fire clay additive in homebrew?

[finebrand]

Hi all... and maybe specifically david s ? I'm mid construction of my oven... all going well thus far, concrete block base, perlite concrete insulation layer, super duty firebrick floor. It's DOME TIME!

(Thanks, by the way, for waving me off he exercise ball approach... not so much for the ball as the perlite material. Didn't dawn on me that it wouldn't have the thermal mass that I wanted until I read it here.)

I'm going to do the sand mound thing and then cover it with homebrew 3:1:1:1 (unless advised otherwise in strong terms). I've got the cement, sand, and lime. What I don't have is fire clay. What I DO have is a big bag of kaolin clay (for coating fruit trees). I'll never use up it for that. Wondering if kaolin would be a satisfactory clay for this purpose. It's not fire clay, per se, but I can't imagine this thing will get hot enough to make that a necessity.

Thus far, I've been unable to locate either stainless steel needles or the appropriate polypropylene fibers here in Portland, so I'm going to have to go without (again, unless someone tells me that one or both are genuinely required and not just nice-to-have.)

And, just to bring it all on topic... if anyone reading happens to know of sources for these remaining ingredients in Portland, I'd love to hear about it.

[david s]

Koalin is fine, it just happens to be at the expensive end of clays you could use. The fine polypropylene burnout fibres are more important than the stainless needles which make handling the mix more difficult. The burnout fibres provide a measure of protection from steam spalling. You should be able to source them from Domcrete supply specialists as they are used sometimes in concrete. I use a two pack Sika product that contains both large, thick polypropylene fibres as well as the short, very fine ones.But just use the very fine ones.My product is called Radmix PPM 48/19 by Sika. There are other similar products by other manufacturers.but try your local Sika dealer.

Just on the fruit tree treatment, how do you apply the clay? I also use it for that purpose but mix it with equal parts of hydrated lime and a little copper sulphate.

[finebrand]

Ah, OK... thanks. Yeah, well, expense is... what they call sunk cost at this point. I already have it. So, better to put it to good use than just have it sit around annoying my wife. I'll take another look around for the poly fibers. That's all I need is flakes of concrete in my pizza.

I believe I read in one of your many instructional posts that you have, over the years, reduced your clay from 3:1:1:1 to 3:1:1:0.5? True? Any other modifications you've stumbled upon that help keep things from degrading?

As for applying the kaolin, this is "Surround WP" which is a sprayable (i.e., very fine) clay (maybe same there?). As you're probably aware, for optimal coverage, you spray the entire tree, but given that you end up with a yard full of ghost trees, I gave up on it for purely aesthetic reasons. I don't mix it with anything, just because it can require multiple applications, so don't want to confuse things. I spray oil, sulfur, and copper at various times, and I tend to keep them all separate just because it's less to worry about with the combinations and temperature and such. I've yet to try just applying it to the fruit selectively. When I lived in Japan, they put little baggies over the fruit. The patience of those people is remarkable. Mine is not. If it gets down to it, I'll go to the farmer's market and have nice looking trees, I've decided.

[david s]

Oh, I misinterpreted your application method. I just paint the mixture on the trunks. I didn’t realise you sprayed whole trees. I've trained my lime and lemon trees over a pergola, like they grow lemons on the Amalfi Coast.

[finebrand]

Oooo... if only. I do that with grapes for my summer moments in Tuscany. We trade our inability to grow citrus for apples and pears and such, but they do get pestered by the flies. So, I *think* the trunk business is about sun scorch there, no? In our case, it's about not giving the flies a place to lay their eggs.

Side note: This happened. Due to the concrete pushing in a bit, it ended up being a little smaller (~28") than I'd hoped at the narrowest on the floor. Should be good enough for the small groups we tend to host (and easier to heat! Silver lining!). The slightly pointy dome is 15". Opening is 9".The bottom is 4" of perlcrete penned in by regular clay bricks. The floor is made of super duty fire bricks-- on the advice of our local refractory manufacturer-- who also supplied the ceramic fiber blanket that goes on next.

Hi-Temp, Inc. is the name of the place, for those in Portland, Oregon USA looking for any of this stuff. They had it all. They wanted to sell me some Mizzou refractory casting, but by my math, that got fairly expensive for this project, so I home-brewed it since I had most of the required ingredients already. It's a backyard pizza oven, not an industrial kiln.

Got it covered with a moist blanket and plastic for now. Probably let it cure for a week or so before I do anything else? I'm currently thinking I'll do a (clay) brick arch for the opening, so maybe a thermal break between the dome and arch? Perlcrete? Or a metal ring as more of a structural break than a thermal one? Is there any sort of expansion differential you'd worry about with a sandwich like that? Maybe it's not necessary. This whole thing is very seat of the pants. The probably more reasonable option would be to cast it and just cap the end with half-bricks for aesthetics.

Decided I was, in fact, too impatient to locate, order, and wait for the fibers after all. Classic me. Kind of like when I tried to dry-pour the top of the base. (Spoiler: Don't do that. Works for posts. Not so much counter-tops.) As I told my wife last night "so far, so good... it's only collapsed once!"

Thanks again for the input, David. After all the reading I've done on here, it feels like a brush with celebrity!