hearth insulation question

[woods witch]

hi everyone I have the foundation poured and the blocks done. I am ready to do the hearth this weekend. I am using your plans for the 42" oven and I have a question about a product that I have access to. It is a material called "Smooth Kote" and I am considering using it to insulate the hearth. It is made of Portland Cement, Fire Clay, loose mineral fibers and silica. It is very light material in 45lb bags. It's used for refractory work as an insulation mix over firebrick and over mineral board. It is mixed with water like concrete and cures the same.......only lighter. I have a whole pallet full and really want to use it. I can't rationalize any reason not to, but this is the first oven I've done. If anyone knows of the product or can think of any reason not to use it, please let me know!!! I can use all the advise I can get...thanks in advance! Jerry

[dmun]

Re: hearth insulation question

At least one maker has insulated with lightweight concrete (AAC) below the hearth. I don't know about the material you're considering. Even if it won't stand up to the 700 degrees of the outside of the firebrick, it might make a fine secondary insulation, isolated by a thin layer of blanket or board.

I suggest calling the manufacturer, ask for an applications engineer, and discuss your plan. They would know a whole lot more about the stuff than I would.

[SpringJim]

Re: hearth insulation question

The silica, fireclay and portland all sound like normal (non insulating) materials. I'd find out what percent is the mineral fibers.

Since you've got a lot of it, it may make a great dome covering, particularly if it has good insulating properties.

Good luck.

[Modthyrth]

Re: hearth insulation question

When I was calling around yesterday looking for local sources of Heatstop 50, one vendor offered up Smooth Kote as an alternate high heat mortar product. I'd be very interested to learn what applications the manufacturer suggests for its use; please report back if you investigate the matter!

[asudavew]

Re: hearth insulation question

Doesn't sound like an insulator to me.

[woods witch]

Re: hearth insulation question

the bag says "insulates up to 1200 degrees @ 1/2" thick". My concern is more about the strength of the product. I haven't had any luck contacting the manufacturer, I'm not sure they are still in business....
the stuff sets like concrete and it's formable. I'm going to pour a small pad in a form to try a "test-run " just to see how strong it seems. the bag does not provide a break down of percentages of materials. I post my results.

[asudavew]

Re: hearth insulation question

the bag says "insulates up to 1200 degrees @ 1/2" thick". .

That's Awesome! Sounds like it's perfect.


I guess those fibers are the key.
Because, without those, the ingredients are similar to poor man's high-heat mortar.

Let us know how it works out.
Maybe a few pictures!

Dave

[dmun]

Re: hearth insulation question

When you do your test, I would suggest pouring a block the size of a firebrick. When it's fully dry, weigh it 8 pounds: conducts heat. 2 pounds: insulates.

By the way, you don't need any particular strength in your insulating concrete. Vermiculite concrete is very weak except for compressive strength.

[asudavew]

Re: hearth insulation question

When you do your test, I would suggest pouring a block the size of a firebrick. When it's fully dry, weigh it 8 pounds: conducts heat. 2 pounds: insulates.

Good idear

[woods witch]

Re: hearth insulation question

talked to bravo guys ,they said as long as it is a insulating concrete product with portland , go for it . I guess try a test block and put a torch on the other side of it a see what happens with heat transfer ????????? any other ideas just chime in thanks jerry

[woods witch]

Re: hearth insulation question

well, it's in....we poured the insulating hearth and are moving on. Next question is about some free firebrick we have. I've read that rule of thumb is that we want to stay away from 2lb firebrick and use 8lb firebrick. Well, we have about 150 white firebrick that weighs 5 lbs. They are 8" long, 2 1/4" thick and 3 3/4" wide. We need advice....we're afraid to use them if it's not worth the chance! Help!

[woods witch]

Re: added link to pictures

Picasa Web Albums - carolyn - wood fired oven
if anyone want to take a peek at our progress....
any suggestions on the firebrick question???

[asudavew]

Re: hearth insulation question

They sound ok to me.
Try putting one in your BBQ and heating it up for an hour or so.
See if it gets nice and toasty.

Then turn the bbq off and see how long it stays hot.

It doesn't sound like they are insulating bricks to me. Those would be the 2 lb bricks you referred to.

Nice work so far!

Dave

[woods witch]

Re: hearth insulation question

thanks Dave! What a great idea....we just put a brick in the oven to see how it holds heat. will post back to report how it did!

[woods witch]

Re: hearth insulation question

turns out what we have is not firebrick....it's basically white sand brick. Glad we checked it out. We just came back from the brickyard with a truck load of firebrick and here we go!!! We are moving right along