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carrieanddan 12-06-2007 12:16 PM

K Fac-19
Has anyone looked into this as a hearth insulation?
It is a mineral wool insulation block. I found this data sheet
The rep at the local refractory supply mentioned it as a possible alternative to ceramic fiber board (which is what I am assuming SuperIsol is, I am having a bit of a tough time finding specs on it.)

For refractory cement he recommended Sparcast 30L, its a 3,000F conventional castable that comes in 50# bags. It seems like overkill, but it is much cheeper than HeatStop from the fireplace supplier.

I am learning way more than I thought I needed to know about refractory products.

Thanks all for your input.


dmun 12-06-2007 01:06 PM

Re: K Fac-19
I used two and a half inches of mineral wool board, insblock19, from Harbison Walker. I bought it from an ebay source, HW wanted almost as much as super-isol for the stuff. 19, btw, stands for 1900 degrees F., so it's not for as high temperatures as the stuff you found, but the outside of a wood fired oven is not likely to get much more than 1000. Insblock19 worked fine. Even a big long fire only warms the bottom of the support slab.

Super-isol is calcium-silicate or cal-sil. It's superior stuff, no question, but it may be a bit of overkill if you are not building a kiln or foundry furnace.

I'd be interested to know if a castable refractory would work as a firebrick mortar. Perhaps you can get a small bag from the vendor and do a test, before you commit. Heat stop is easy to mix and use, and that's a plus.

carrieanddan 12-09-2007 05:37 PM

Re: K Fac-19
I have decided to go with the K Fac-19. As a bonus it is cheap! less than vermiculite and concrete, and a lot less work.

When I went to the warehouse to look at things I found that they have mortar for firebrick, he apparently was a little confused as to what I was looking for.
I am still a little leery of getting my mortar from them, I don't know if it is a problem to have a mortar that is rated to 3000 degrees.... They build industrial ovens etc... I am worried that a 3000 degree mortar would have the same problems that a Heavy duty (high heat) firebrick would cause (not holding heat, but reflecting it all back making the oven too hot). Any thoughts?

jpar 12-10-2007 12:35 PM

Re: K Fac-19
Kfac boards, along with conventional ceramic fiber boards, are fibrous products. As they see temperature, the binders burn out and these products loose strength. Super Isol and similar cal-sil boards have much higher compressive strength, and will not compress under the weight of the oven and hearth.

Les 12-10-2007 01:19 PM

Re: K Fac-19
I see the hight temp mortar as a plus. In regard to your concerns of the oven getting to hot - I don't know if that would be possible, and if it is, just add less wood.


bolex16mm 03-24-2008 01:29 PM

Re: K Fac-19
I am considering using K Fac-19 mainly because I can get it locally. The shipping costs for the FB board are nearly one half of the cost of the boards. However, I don't want to do something foolish because I can save some money. How long of a period of time are we talking about for the K Fac-19 product to break down. Thanks in advance for the info on the insulation boards.

beaglestorm 03-24-2008 03:07 PM

Re: K Fac-19
I am also going to be using Insblock 19. For comparison it looks like the KFac has 4800 PSF of compression strength vs 5472 PSF for the Insblock 19. The Modulus of Rupture is 95 PSI for Kfac vs. 115 PSI. And both of these are lower than the Super-isol specifications. I had both available here locally as well, I only chose Insblock because of the good reviews it got here on the forums. Good luck.

Oh and the insblock has a simillar disclaimer on their spec sheet here:

INSBLOK-19 is a 1900F maximum service temperature lightweight mineral wool block insulation. INSBLOK-19 exhibits very low thermal conductivity, good moisture resistance, easy handling, and easy cutting. Its organic binder gives INSBLOK-19 excellent cold strength but will dissipate above 475F. INSBLOK-19 meets the ASTM C612 Class 5 specification. Its principal application is as a backup lining to lower furnace shell temperatures.

dmun 03-24-2008 03:33 PM

Re: K Fac-19

Its organic binder gives INSBLOK-19 excellent cold strength but will dissipate above 475F.
That's interesting, since it's primary use, when I researched it, was for the exterior of ceramic kilns, outside the insulating firebrick layer. Ceramic kilns are fired to red heat repeatedly, and their floors are weighted down with pots and heavy kiln furniture. (Think about a stack of five or six pizza stones held apart with ceramic pillars, each layer with a load of heavy pottery.) You'd think it would hold up to oven conditions (800f, and the weight of a pizza or two.)

In my case it seems to have, although I'm not going to tear it apart to measure it.

beaglestorm 03-24-2008 05:00 PM

Re: K Fac-19
Well using the most rudimentary of calculations.

150 dome bricks + mortar weigh about 1200 pounds.

51" diameter total area including dome and floor = 2043 sq/in
42" floor area = 1385 sq/in

Subtracting floor area from total area (not accounting for the door opening) gives a total of about 657 square inches of area underneath the weight of the dome.


1200 lbs / 657 sq/in = 1.8 PSI way way below the 38 listed in the specifications.

This seems way too low. Can you check my math? What am I missing? Even if it is 50% off, either product should hold up fine.

jpar 03-25-2008 05:14 AM

Re: K Fac-19
According to my understanding, Insblock 19 is relabeled K Fac 19. In industrial kilns and furnaces, these products are almost never used in areas where structural strength is needed. They are typically used in sidewalls and arches. If they are used in hearths, boards are put between firebrick piers.

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