insulating floor

[peter]

I know this is probably the stupidest question ever posted here but here goes: I am about to pour the insulating floor of my oven, the renforced floor is done and the perlite is awaiting my attention. On page 22 the verbal instructions indicate the floor needs to be upon at least 3 3/4 inches of insulating concrete. The photo, on the other hand, show the floor bricks flush within the 7 1/2 in forms. 3 1/2 inches for the support structure leaves only four inches left till the top of the form. Do they mean the overall thickness of the insulating layer is four inches and the floor firebricks are still insulated sufficiently on the bottom?

[dmun]

Re: insulating floor

I don't have the page you're refering to at hand, but four inches of perlite/vermiculite concrete or two inches of Cal-sil board are recomended.

[DrakeRemoray]

Re: insulating floor

That page looks like the the old "island" method. What dmun said is correct. 4 inches of perlcrete on top of your supporting slab...

Drake

[mfiore]

Re: insulating floor

The directions state the perlite/vermiculite OR the Cal-Sil board, yet most of the ovens I am looking at in the forum that use the board seem to put it on top of the Vermiculite concrete. Is this a superior way to go, or is it overkill?

[DrakeRemoray]

Re: insulating floor

I would say that is overkill. Why go to the trouble of mixing and pouring perlcrete if you are going to buy the cal-sil boards?

[mfiore]

Re: insulating floor

That's what I wanted to hear! Anyone disagree?

[CajunKnight]

Re: insulating floor

mfiore:
When you are talking about heat transfer its not really overkill. Both do a great job but combined they are better. So you have less heat transfer and a much more efficient oven. Faster to heat up with less fuel and easier to maintain temperature for the long haul.

It really ends up being what you can afford to do.
If you are not worried about any of those items then a simple earthen oven with clay and grog mixture is good enough. Or is it? Its a personal choice that comes from the wallet.


peter:
The picture you referred to shows the bricks layed into the perlite/concrete. The best setup is to let perlite mixture harden and spread the fireclay or brickdust from cutting over the top for a smooth surface and then lay your bricks on top of that. Now with that being said I have not yet built an oven and going strictly on information gathered in this forum.

[mfiore]

Re: insulating floor

mfiore:
Both do a great job but combined they are better.

Does anyone know how much better? Is the difference significance? How about two boards stacked atop each other. This should be even better yet, but does anyone know if the differences are significant (compared to a single 2 inch board)?

[Dutchoven]

Re: insulating floor

Fron an installation point of view 4 inches of perlcrete is about equivalent in insulation value as 2 inches of cal-sil board insulation...so if you did 4 inches perlcrete and 2 inches cal-sil double the insulation better...since the floor is the hardest to keep hot it is worth the extra by far and wide...definitely not overkill...IMHO
Best
Dutch

[mfiore]

Re: insulating floor

How about 4 inches of cal sil? (two boards stacked on top of each other)?

[DrakeRemoray]

Re: insulating floor

How about 4 inches of cal sil? (two boards stacked on top of each other)?

That would be more, but I still say overkill.

I certainly don't think you get any benefit from using two different types of insulation. That is, no need to pour perlcrete AND use insulating board. If you are going to pour perlcrete, just pour as much as you think you need. I have 4" of perlcrete, no problems maintaining floor temps, and a 350 degree oven 18 hours after firing. I stand by my overkill statement.

Drake

[dmun]

Re: insulating floor

I have 2.5 inches of insblock19, which is not as good an insulator as cal-sil, under my brick floor, and my support slab seldom even gets warm. I think either/or is perfectly good.

[thebadger]

Re: insulating floor

I went with 3 1/2 inche of perlcrete mainly to help raise my hearth...

I then got the cal sil that sits on top...

+ cal sil will provide more insulation on top
+much easier to level your bricks on the your hearth
-cost/shipping

I agree - you don't have to use it but it can't hurt if you have a little more money in your budget. I opted for the FB blanket as well.

My 2 cents.

Dick

[SpringJim]

Re: insulating floor

If you do choose to overkill, I believe the hearth is the place to do it!

[DrakeRemoray]

Re: insulating floor

I am ok with overkill, I just say (like dmun) do either/or. 8 inches of FB board? Fine! 12 inches of perlcrete? fine! But unless you have some specific reason (like badger trying to get the hearth at the correct height) choose either perlcrete or FB board.