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readie 06-13-2007 08:32 AM

Advice re the insulating hearth
Hello I have a question about the Insulating Hearth: does it matter if the vermiculite insulating concrete layer is poured onto the structural concrete once it is dry? I notice that the guidelines here suggest doing it at the same time so it all bonds together, but unfortunately I discovered this forum too late and have already done the structural layer!

If it is too late for me to add the vermiculite layer I was thinking of using the Superisol block instead. Does anyone know if this is available in the UK?

Any help would be much appreciated! Thanks. :)

dmun 06-13-2007 09:40 AM

Re: Advice re the insulating hearth
There is no problem laying the vermiculate concrete after the support slab is dried. Even if it's completely detached (which it won't be - the water and concrete settle to the bottom) it doesn't matter. All the force is down.

The main difference between calcium silicate block or equivilant, and vermiculite/perlite concrete, is that you can get away with two inches of insulation rather than four.

james 06-13-2007 09:46 AM

Re: Advice re the insulating hearth
David has it right.

We are looking for a source of Cal Sil (or Alu Sil) boards in the UK and will let you know when we find something. For now, you can definitely pour a 4" vermiculite layer on top of a curing slab. Gravity is on your side. The comments about same day pour go back to the very, very early days, when some builders were putting the vermiculite layer under the slab, and hanging the whole thing with rebar.

If anyone finds "pour the same day" mentions on, let me know, and I will delete them.


readie 06-13-2007 10:01 AM

Re: Advice re the insulating hearth
Thats great, thanks for getting back to me so quickly, very reassuring.

FYI: I got the "same day pour advice" from:

where it states "It is important to pour both the insulating and thermal layers in the same days, as you want them to bond and cure together".

Thanks again for the information. Really helpful.


JoeT62 06-13-2007 11:44 AM

Re: Advice re the insulating hearth
Excellent! I was planning on pouring the same day, but a staged approach will let me get them both done sooner (I have to squeeze construction hours in whenever I can).

RTflorida 06-13-2007 03:20 PM

Re: Advice re the insulating hearth
WOW! Wish this had come up 3 months ago. I followed the instructions to the letter. Made sense at the time, so I didn't ask. I then proceeded to mix ALL of my concrete by hand (yes, pretty stupid, I'm not 1/2 the man I thought I was) and do BOTH pours the same day. I can't believe I didn't have a stroke and a heart attack.....the 1 week wait for curing allowed my back and shoulders time to recover.
I'm not an advocate of hand mixing, but it sure would have been easier knowing I could have taken a break between the 2 pours.

james 06-14-2007 05:45 AM

Re: Advice re the insulating hearth

I feel terrible. But look on the bright side -- your hearth did fuse, and it will be that way forever. Hope your back has recovered.

If it helps (which I know it doesn't), I have changed that page on the web-site plans. Sorry about that again.


RTflorida 06-14-2007 07:04 AM

Re: Advice re the insulating hearth

no apology needed. My ego (I can do anything) got the better of me and I proceeded to mix 60 bags of concrete by hand. I struggled with the rental/buying options of a mixer, then said screw it and just started mixing.

Having the option to pour them separately would have been nice, but the more I think about it, the more satisfied I am that my oven is as structurally sound as it can possibly be.

DrakeRemoray 06-14-2007 08:17 AM

Re: Advice re the insulating hearth
I did the same thing (pour both on the same day). My next door neighbor pulled me out of the fire on that day. He and his son came over and really really helped. I am sure I would not have been able to do it without them.

So pretty much every time I make pizza I either invite them over or at least hand one over the fence!


BamaGirl 08-19-2007 10:27 PM

Re: Advice re the insulating hearth
I poured both today. How long do I have to wait to start laying the cooking floor?
Also, What is the best way to cut your forms using foam and how to you get them to stay in place?

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