Vermiculite 4" 5" 6" Does it matter?

[fxpose]

I searched but I couldn't find an answer.
Does it make any difference whether I use 4" or 6" of vermiculite/perlite insulation under the floor? Is there any downside going with 6" as far as placing bricks on top? I understand the R value will increase but is it better than going with the recommended 4"?

Thanks!

[eprante]

Re: Vermiculite 4" 5" 6" Does it matter?

I think it was Dmun who said, you can have too much thermal mass, but not too much insulation. I have 5" under my floor.
Eric

[fxpose]

Re: Vermiculite 4" 5" 6" Does it matter?

I guess what I'm trying to ask is will there be any 'settling' as you go thicker? I know it has good compressive strength but over time will they eventually settle somewhat under the weight of the oven?

[Neil2]

Re: Vermiculite 4" 5" 6" Does it matter?

"I guess what I'm trying to ask is will there be any 'settling' as you go thicker?"

No. A vermiculite/perlite/portland mix will not settle to any appreciable degree.

[fxpose]

Re: Vermiculite 4" 5" 6" Does it matter?

Thanks Neil, that's exactly what I wanted to hear.

On a related note, is it all right to place the vermiculite/portland mix over a freshly poured slab, giving, say, a couple of hours setting time in-between?

[RTflorida]

Re: Vermiculite 4" 5" 6" Does it matter?

'Back in the day' when I built my oven, it was recommended to pour the insulation layer the same day as the support slab. The idea being - the slabs will bond together better. As we all know, nothing is going anywhere once it is all built, so the bonding theory is debunked. Many have waited a day/week between pours, since those original instructions were posted.
It is entirely your call based on time and energy level, take a day or two off, or go straight to the insulation layer.

RT

[fxpose]

Re: Vermiculite 4" 5" 6" Does it matter?

Thanks RT, that's exactly what I thought. I can do both on the same day as there will be no re-forming to do. The insulating layer will be formed exactly like the slab.

[Neil2]

Re: Vermiculite 4" 5" 6" Does it matter?

I would wait a day or two. I would then check that there is no dishing or ponding on the new slab and fix it with a bit of grinding. You want the vermicrete layer to drain out if any water gets in.

[Tscarborough]

Re: Vermiculite 4" 5" 6" Does it matter?

To the original question. It is a (non) simple engineering question to calculate, but the reality is that 4 to 5 inches will probably not become heat soaked (thus requiring more depth) in the time frames we are operating the ovens.

As for the compressive strength, my brick chimney is sitting on up to 24 inches of 8-1 perlcrete and I have no concerns of settling at all.

[fxpose]

Re: Vermiculite 4" 5" 6" Does it matter?

I decided I'm going to instead use an insulating board over the slab as I found a local dealer who sells 2" and 3" boards in 24"x36". The 3" boards are less expensive (per sheet) than the 2" boards. The 3" boards are more dense as well (per cu/ft). Are they not as effective as 2" boards?

[kebwi]

Re: Vermiculite 4" 5" 6" Does it matter?

I must admit, I've been confused about the density of insulating materials as described on FB. Intuitively, I would have assumed that less dense means better insulating, but 6# blankets are regarded as better than 4# and worse than 8#, so that just doesn't make any sense to me.

With regard to the boards you found, what kind of board are they? What are the specs?

[fxpose]

Re: Vermiculite 4" 5" 6" Does it matter?

With regard to the boards you found, what kind of board are they? What are the specs?

Here they are:

Ceramic Fiber Board

I'm confused as well...

[kebwi]

Re: Vermiculite 4" 5" 6" Does it matter?

I see your point. My theory would be that the manufacturing process for the less dense material is significantly more difficult and expensive, but that's just a theory. Maybe the denser stuff is in much higher demand, thus is produced in much greater bulk, thus driving its price down.