Building in Central Florida, Question about insulation beneath cooking floor

[glowthb]

First let me say hello and thanks to all that post here...been learning alot.

I am getting ready to pour the hearth for my new brick oven but am looking at different options for the insulation beneath the cooking floor.

I have been able to locate large perlite at the local hydroponics store if I go with perlite/cement insulation medium.

Or I also found at a pottery supply center "Soft Straight K-23 Firebrick" that are used for insulating Kilns. They are the same size as fire brick, 9x4.5x2.5, but weigh only two pounds.

1. What are your thoughts on which is better for beneath the brick cooking floor?

2. If perlite cement mixture is used, how thick does it need to be? Looks like 4" according to the Pompei building guide.

3. Does anyone have any experience with the K-23 bricks?

Thanks.

[Jed]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Hi glowthb,

I don't have any experience with the light weight brick.

I can say the mixture detailed in the FB Pompeii plans, with four inches of perlite / cement mixture, works. It is a known and proven technology.... I'd stick with what is proven.

JED

[Tscarborough]

Re: Building in Central Florida, Question about insulation beneath cooking floor

The K-23 run about 9 bucks a pop here, while perlite is pretty cheap. They will work well, if you can afford it.

[glowthb]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Thank you.

The K-23 here is $3.75 a brick, with Perlite at $35.00 for a 4 cu. foot bag the costs are relatively the same.

So the issue comes down to efficiency. K-23 vs. Perlite/cement.

[GianniFocaccia]

Re: Building in Central Florida, Question about insulation beneath cooking floor

I believe it has been noted here that perlite/vermiculite has the same insulating value as insulating firebrick (IFB). The 3" base of my oven-floor insulation is 8:1 vermiculite and although it took a small amount of work to install, it was an easy project. I topped this layer with 2" of Insblock 19.

For the same depth (4") you would need approximately 120 IFB vs two 4cuft bags (I paid $29 ea) of vermiculite to properly insulate the bottom of a 42" oven.

John

[glowthb]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Gianni..and all thanks for the advice. I want to make sure I understand the comments so I use the best material available locally.

1. Insulated fire brick (IFB) and vermiculite/perlite would both require 4 inches to get the same insulation? So the single 2.5 inch layer of IFB would not be sufficient insulation?

2. What is Insblock 19?

Thanks again.

[GianniFocaccia]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Yes, the FB plans call for either 4" of vermiculite/perlite insulation or 2" of an insulating fiber board. A growing number of builders are incorporating a combination of the two. Insblock 19 is popular with builders because it is effective and reasonably priced. A good discussion on it can be found here:

http://www.fornobravo.com/forum/f6/k-fac-19-a-3031.html

[ThermoJax]

Re: Building in Central Florida, Question about insulation beneath cooking floor

I am in North Florida and I got the insblock 19 from atlantic firebrick here in Jacksonville. It is great stuff. I did not use the Vermicrete. I also purchased the related blanket product for wrapping the dome. I was worried as my concrete pad was warm during the curing process, but it is not warm now. I also put a bunch of r-13 insulation over the ceramic insulating blanket. The Vermicrete mix looks hard to use and I think it might take a while to dry enough for the next step. Purchase the insblock 19 and forge ahead.

Good Luck

[dmun]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Insblock19 is the brand name of the mineral fiber board made by Harbison-Walker, the nations biggest refractory manufacturer. They have distributors all over the country, but I found I could buy it for less elsewhere. It's good stuff.

[azpizzanut]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Hello,

K23 insulating brick is often used in ceramics kilns. There are other insulating fire bricks to consider though, K29 for example.

I made a 42" insulating hearth from Thermo Ceramics brand Kaolite. Three bags @ $45 per bag. It is a castable insulating refractory product. My wife made a brick paver from the small amount left over and it is light as a feather. Another hearth has four inches of perlite/portland (5:1) with one inch of Kaolite on top of that. Overall, the most cost effective is perlite/portland. Do wear a mask when handling pelite, cough, cough !! The dust is easily raised no matter how careful you are.

Shop around for perlite. I bought a 6 cu ft bag at a builders supply for $28. HD has commercial grade perlite available 2 cu ft for $17.....go figure. The product from the builders supply said in small print "Water resistant". However, it mixed as easily as the perlite from HD, no problem at all.

Cheers,

[SteveP]

Re: Building in Central Florida, Question about insulation beneath cooking floor

$35 for 4 cu ft bag of Perlite seems pretty high. I paid $9 for 4 cu ft bags of perlite at a nursery supply warehouse in Ft. Pierce. I used to live in Winter Springs and I would assume you would be able to find it cheaper than $35/bag.

[Tscarborough]

Re: Building in Central Florida, Question about insulation beneath cooking floor

10-12 bucks for 4 cubic foot is reasonable. 35 bucks is robbery.

[azpizzanut]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Yikes ! HD seems to sell a lot of it though.

Cheers,

[efleifel]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Hello,

A message to glowthb.

I live in Oviedo as well, and was able to get all the material locally. I got the vermiculite from Lucas Nursery, and the firebricks and the HeatStop mortar from Cemex; corner of Forsyth and Aloma.

Let me know if you still have questions or if you are already on your merry way with the build
good luck

Eddie
Salute
My Web site

[glowthb]

Re: Building in Central Florida, Question about insulation beneath cooking floor

Thanks for all the input.

I had an engineer at work take a look at the data sheet for the K-23 and Insblock 19. The K-23 is only marginally less efficient as an insulator then the insblock 19 so I went with the K23 I could get locally. I had already purchased vermiculite from Lucas but it was the fine agricultural grade. I decided to vermicrete around and over the K-23 so there is about another inch of vermicrete over the K-23.

I am not to pleased with how the vermicrete set. Seems more like packed soil or cork after 48 hours of drying. Not sure if I should pour a slurry of concrete over the vermicrete and let it set some more or not. The vermicrete appears to be very firm from the top but I am concerned once I pop the form off the edges may have some crumbling. I may frame it with some Hardibacker to hold it together.

Eddie, I got the fire brick and fireclay over by Dogtrack Road at Harwood Brick...$1.25 a brick.

I was hoping to begin the oven this weekend but may need to re-assess this insulation layer before I move forward.