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waitingtocook 03-25-2007 06:08 PM

Super Isol Question
Hi folks, just a quick question. I am going with the super isol board over the vermiculite concrete on my hearth, but my querie is when do i attatch it? Do I need to put the board down on the wet concrete or do I wait for the concrete to cure and dry before I put the super isol on? If so, how do I attatch it to my concrete hearth? Is it ok do you think to have a sort of border of concrete inside of which the superisol will sit? I've heard this stuff is pretty thirsty and sucks the moisture out of cement so I'm leaning towards letting the hearth cure before i put it on but and help would be hugely appreciated.

johnrbek 03-25-2007 06:44 PM

Re: Super Isol Question
Let your concrete slab cure.. keep it wet and covered with plastic sheeting for as long as possible.. one week minimum. the longer you let it cure, the stronger the slab will be.

James sells an adhesive for the super isol if you prefer... I've spoken with a refractory dealer and he didn't see any problem just setting the insulation board down on your concrete slab with no adhesive at all... if you think about it, your putting alot of weight on top of it and coating the entire dome surface with additional mortar and insulation... and then encasing the entire structure either in mortar or with walls... personally, I won't be gluing my insulation board down.

So, put your insulation board down after your concrete slab has cured and dried out a bit, and then if you're still concerned with it sucking up moisture, then put some foil down or something... I haven't heard whether or not you still need the fireclay/sand mixture when going with the insulation board... perhaps someone can weigh in.. In may be that you have a flat enough surface at that point anyway...


dmun 03-25-2007 07:20 PM

Re: Super Isol Question
I laid my insulation board directly on the wet concrete of my support slab.
I didn't use super-isol, but a competing product by Harbison-Walker. I don't think what I used had the extreme water absorbsion of the super-isol. I'd be a little concerned that putting it on top of vermiculite concrete, which doesn't have a smooth and flat surface, it might not lay flat. As JB points out, they make a refractory adhesive for that, but since we are only up to 900F or so, that may be overkill. I would think a smooth layer of concrete based tile mortar would lay it flat and sound if the insulation boards seem to be rocking when you lay them down.

Hendo 03-26-2007 06:59 AM

Re: Super Isol Question
1 Attachment(s)

I’ve found some Calcium Silicate insulation boards here in Adelaide, but I know of distributors of this product in Melbourne. You may have sourced it already, but let me know if you haven’t.

I have decided to glue the insulation boards down on my (well-cured and levelled but not exactly flat) hearth slab with a locally available product. It bonds fibre or fibre boards to itself as well as to brick or steel according to the blurb, so I assume it will do the same to concrete. I’ve only used a little to date to glue a few fractured corners back and it works a treat! So I’m hoping it will do the trick for sticking the boards down on the concrete. It’s good to 1000°C. Send me a private message if you want the details.

One thing for sure is that the insulation boards are very rigid, and given that the adhesive will only bridge around 2mm or so, I took to filling the slight depressions in my hearth slab today with a runny mortar of fine washed sand (like they use for in-between pavers) and Portland cement. I’ll know tomorrow if it’s worked and will commence gluing the Cal Sil boards down after it’s cured for a couple of days or so. I did look at levelling mortars for floor tiles, but was advised (by the suppliers) that most are only good to 50 – 60°C or so.

However, I think David’s method of placing the sheets down on the wet concrete is by far the simplest way to go, and I think I’d do it this way if I was doing it again and I had a plain slab (I have thermowells sticking up all over the slab to contend with - see pic below!). The pro side is that it would assist in getting the concrete flat, and you wouldn’t have to worry about levelling any small depressions in the slab after the event. The con is that the boards will suck out moisture from the curing concrete, and a moist cure for your slab will not be as readily achievable. I really want to keep the insulation as dry as possible for as long as possible. But it sure would be a lot easier, and if I’d done it this way, I’d be on to laying the floor and dome by now!

Good luck with your build.

Cheers, Paul.

jwnorris 03-26-2007 08:01 AM

Re: Super Isol Question
After several attempts to get the SuperIsol board wet enough to allow me to spread some Refrax mortar [unsuccessfully, I might add], I can to the realization that the components of my Casa 110 were of such weight that they were not going anywhere. As I had leveled the base structure, I was not concerned about the floor being level.


johnrbek 03-26-2007 09:45 AM

Re: Super Isol Question
Hmmm.. good points.. I didn't decide to go with insblok 19 till I already had a cured slab... setting it down on an uncured slab certainly would seem to eliminate the issue of obtaining a nice level surface first... Fortunately, my slab ended up nice and smooth, so this isn't an issue for me... If you do go this way though, I'd make sure that you have a way to keep rain off the work area until you're pretty much complete with the job... Not sure about cal sil board, but the insblok 19 seems to get pretty mushy when wet... I accidently got my wet and was surprised at how mushy it was.. I opted to dry it out before proceed to lay down the hearth bricks and rigged up a tarp over the work area to ensure it remains dry during the remainder of the project.. again, not sure about cal sil products...


james 03-26-2007 09:59 AM

Re: Super Isol Question
I talked with the producer of SuperIsol early on, and they seemed confident that it would not go mushy and would just dry out. I got a sample very wet, and it held up OK.

I am going to ask them what they think about setting it in wet concrete. It could be a time saver, but I think it is worth asking them if they think that is a good idea.

If you have a cured slab that isn't entirely level, you can get your SuperIsol as level and smooth as you can, then use your under floor sand/clay layer to set your floor perfectly smooth.

I will also ask if the small amount of moisture in the fireclay/sand mixture would cause a problem. I can't image that it would, but it's worth asking.

For everyone setting their floor on either a thin bed of sand, or sand/fireclay, I think the comment that "gravity is on your side" is a good one. My Scott ovens have the floor set in the sand/clay mixture and they are not moving.

Hendo 03-26-2007 10:14 PM

Re: Super Isol Question
3 Attachment(s)

Originally Posted by dmun (Post 9057)
I think play sand would work fine as a leveling medium.

Thanks for this David. The use of sand between the insulation layer and the floor does seem to be quite common here, at least in the commercial arena see pics below.


Originally Posted by johnrbek (Post 9060)
I'm using insblok 19 and it's kinda brittle/fragile... I would think even if you glued it, under pressure it would probably just break away anyway...

My Cal Sil boards are quite fragile too, and Im hoping that the heat resistant adhesive will fill some of the (< ⅛) voids between the slab and the underside of the insulation boards to give as much support as possible over the entire area. This was the main reason I decided to glue them down, after first filling up any low spots in the slab as much as possible.


Originally Posted by jwnorris (Post 9061)
After several attempts to get the SuperIsol board wet enough to allow me to spread some Refrax mortar [unsuccessfully, I might add], I can to the realization that the components of my Casa 110 were of such weight that they were not going anywhere. As I had leveled the base structure, I was not concerned about the floor being level.

Another tick for sand, or some sort of dry-mix product! I will, however, try placing a ring of refractory mortar around the outside bottom edge of the first dome course to seal the oven, as a number of people have recommended. Ill let you know how I get on.

Thanks, Paul.

james 03-27-2007 12:39 AM

Re: Super Isol Question
Hey Paul,
Quick question. How thick is your sand bed?

Hendo 03-27-2007 05:50 AM

Re: Super Isol Question

Photo's were provided by a commercial installer, who coincidentally imports ALFA Caminetti ovens from Italy.

Correct me, but could the surrounding bricks be insulating firebricks? I've never seen anything like them, but the sand base for the floor appears to be the same height.

The company also markets a gas kit, which was the main reason for my contact, but it also sent me a series of photo's showing a very ritzy oven construction at a ranch somewhere in New South Wales. (BTW, the gas kit is way over the top and very expensive, and importantly one can't use any other fuel, so I've passed on that one!)

Anyway, this company and others I've approached here about off-the-shelf ovens quite often recommend that the floor be installed on a bed of sand, rather than other insulating materials like vermiculite concrete or Cal Sil board.

Cheers, Paul.

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