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]

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]

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]

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]

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]

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]

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 (K Fac-19)

[ThermoJax]

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]

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]

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,