we have built the base.....

[JUBILEE]

greetings from queensland australia! we have been pouring over all the information on this site and the forum and all the suggested other info and we have found it really useful. we thought we would just be knocking something together in the backyard, but as we started it just got more complex and now we are totally obsessed with it! we have just built the base and we are ready to pour the hearth. we are deciding whether to use perlite or vermiculite. from what i've read vermiculite can have a mind of its own. russell jeavons suggests perlite but without too much detail. can anyone share their opinion on each? thanks

[dmun]

Perlite and vermiculite both work the same. Perlite has the advantage of being white, so you can see when the portland cement is combined before adding water. It's mostly what's available and affordable in your area.

[asudavew]

I used both.

I found the verm much easier to work with.

The perlite(i used the course) had very tiny pieces that would blow everywhere.
It especially liked to end up in my eyes! USE GOGGLES!

But the verm stayed where I put it, even when the wind was blowing.


Dave

[gjbingham]

I used a 5/1 mix verm/cement, measured by a one gallon pitcher. The stuff always set up within 24 hours.

[JUBILEE]

thanks everyone. it so great to get assistance so quickly! we can easily get verm and perl from the same place for the same price so that makes it hard to decide. what do you think about making the entire hearth out of the insulated concrete or are we best to do 2 layers? one reference i have says insulation layer then reinforced concrete on top and another reference says the other way around? we will be laying the hearth then an igloo style oven on top. so the bits of the hearth that stick out we were thinking of tiling. is it ok to tile onto the insulated concrete? do both perlite an vermiculite give a similar surface and hardness? we have bought the most fantastic chimney from a demolition yard here so i can't wait to see it all finished, we just have to get though all the technical stuff first! we have made a nice round paved area in front of the oven so we can sit there and dream for now! i'll post some pictures when its worth looking at.

[dusty]

Hi Jubilee and welcome aboard. I used vermiculite for my insulation layer, but be sure to remember, it is JUST an insulating layer. It has absolutely no stuctural value. Very important to lay a 3 1/2 to 4' structural layer - with rebar - first. Then the insulation, which ever you choose, can be poured on top. Just as the insulating layer has no strctural value, the structural layer has no insulating value. So you must have both and have them in the proper order.
Hope this makes sense. I'm looking forward to watching your progress and will help anytime if I can.
Have fun building! I sure did.

dusty

[asudavew]

Definately do the concrete first for strength.

Then do the insulating layer on top of that.
Otherwise you would be heating up your oven and the big layer of concrete under the oven.

Dave

[JUBILEE]

i'm glad i know all that now! will it still be ok to tile on the reinforced concrete bits or should we keep the insulated section just under the oven floor and walls and standard reinforced concrete around the edges? once i get my head around this i don't think i'll have to ask too many more questions! thanks all.

[gjbingham]

Jubilee,
I did mine as you just suggested above. Its kind of a pain because you end up doing another pour, concrete, vermicrete, then concrete again around the insulating layer. Its not that much concrete though, so it only takes a little time for the last two pours anyway. If you do it that way, you should have no issues with tiling the edges of the concrete hearth.

I recommend that you premix just a bit of the vermiculite or perlite and cement just to get a feel for the stuff, and to understand what the final set looks like. I don't think the set verm. is suitable for tiling. Little grains of the stuff keep coming off every time you touch it.

[gjbingham]

BTW,
The photo gallery has many great designs for different ways to build your hearth. I like the way Dave did his: http://www.fornobravo.com/forum/phot...ndex.php?n=656