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readie 07-03-2007 08:11 AM

Vermiculite fire bricks
I would be very grateful for advice about this: Do you think these firebricks would be suitable to use as the insulating layer on the hearth? Multifuel fire bricks (item 220125247235 end time 05-Jul-07 12:45:41 BST)

and what about this fire cement to use as the mortar? Fire Cement for woodburning stove & Flue pipe (item 110143861804 end time 08-Jul-07 11:05:20 BST)

Any help much appreciated.

Simon :)

enz 07-03-2007 09:14 AM

Re: Vermiculite fire bricks
These are insulative concrete blocks. They would work for insulation under the cooking surface, but never for the oven itself, it would never heat properly.


nissanneill 07-03-2007 03:21 PM

Re: Vermiculite fire bricks
I have jist completed a Pompeii and covered the outer dome with 3" of vermiculite cement and also buried a 1" thermal blanket under that. When it is 500C inside the oven, the outside dome is COLD. Vermiculite is an insulator and basically does the opposite to what you want. You need a brick that will ABSORB the heat rather than repell it.
As far as the cement is concerned, I would check with the manufacturer some more specific detail. I am not sure whether these pre-mixed products have a use-by date which needs to be known before spending your money. The company selling the goods look like they specialise in refractory materials and may be fine.
It looks OK from the scant detail provided but then again I built my oven using a simple mortar containing cement, lime, fireclay and sand. The ancient Romans didn't have these special high temp cements and their ovens have stood up for over 1000 years.


Archena 07-03-2007 05:16 PM

Re: Vermiculite fire bricks
Yeah, but some Roman geek would have used them if he'd had them! Anything worth doing is worth overdoing!


I should leave now, huh? :o

readie 07-03-2007 10:58 PM

Re: Vermiculite fire bricks
Thanks for comments: I didn't make myself very clear: I was thinking about using them as the insulation layer under the base of the oven (ie instead of pouring vermiculite or using Superisol insulating block), so it sounds like they would be suitable for this. I have been looking into the insulation layer and it seems that Superisol (or the equivalent) is hard to get hold of in UK without buying largish quantities. I thought that using these vermiculite bricks might be the equivalent of a "vermiculite pour" without the "pour"! (not that I'm lazy or anything..).

nissanneill 07-03-2007 11:39 PM

Re: Vermiculite fire bricks
This particular "pour" is a very easy task and is very efficient insulator.Simply dry mix vermiculite, 5 parts to 1 part portland cement, add enough water to make an oatmeal consistency, place in position and float off level.
This would be far better than the bricks because you need to insulate the whole floor area, even out under the dome bricks.
See my Pompeii oven construction pics and description on:

permalink #2.


dmun 07-04-2007 09:43 AM

Re: Vermiculite fire bricks
The old vermiculite block is an underrated insulator. I use a little hunk of it for hardening steel parts: I hold one corner with my fingers and bring the part to red heat with a torch a couple of inches away. My fingers don't even get hot.

It's been superceded by superior materials like cal-sil and mineral wool, for furnaces and such, but we're talking about under 1000 degrees f. here guys. Use it if it's affordable and available.

readie 07-05-2007 08:03 AM

Re: Vermiculite fire bricks
Thanks again for the info everyone.

dmun, you say to use it if affordable and available: the bricks are 25mm thick: do you think one brick layer (ie a 25mm thickness) would be enough to adequately insulate, or would I need to use 2 bricks worth? I am quite keen on using as thin a layer of insulation as possible as the hearth height is already at 90cm, and I am worried that after a 4inch vermiculite pour plus the oven brick it will be over a metre to the opening.


dmun 07-05-2007 09:44 AM

Re: Vermiculite fire bricks
I don't think one inch (25.4mm) of vermiculite in any form is going to be enough insulation. With the best insulation available (cal sil) you can get down to two inches, but one inch of vermiculite is going to leak heat and waste wood. You're in the UK, right? Firewood is an expensive import there. There's another thread this week about the front of an oven being to hot to work in, and how to vent it. I suspect that this is an underinsulated oven.

Archena 07-05-2007 05:12 PM

Re: Vermiculite fire bricks

A meter is just over standard counter top height - why would that be a problem? Actually, a bit over standard would be a good working height for an oven, I would think.

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