The hearth questions and progress pictures

[George T]

I bought my material for the hearth. Both the insulating hearth and the structural. Can these both be poured the same day? Do I pour both the same size? The instructions say you can pour the insulating hearth smaller....how much smaller? Sorry for all the questions..


Below I have started my pictures to show progress
Picasa Web Albums - George - George T's Pi...

[DrakeRemoray]

Yes, you can pout both layers at the same time. You would only make the insulating layer smaller if you want to attach your enclosure directly to the structural layer.

Hope that helps,
Drake

[Frances]

Originally Posted by DrakeRemoray

You would only make the insulating layer smaller if you want to attach your enclosure directly to the structural layer.

...which could be quite a good idea.

The vermcrete insulation layer is a bit crumbly even when its dry, specially round the edges... so if you pour it and inch or two smaller than the structural hearth and then fill the gap with concrete (making a kind of concrete frame round the insulation), the exposed edges will be stronger. Or you can leave out the concrete edge as Drake said and build your enclosure directly on the structural hearth - that will also make it all a bit stronger.

This is what I would do if I built another oven... but having said that, if it seems like too much messing about, your oven will work perfectly well if the insulation hearth and the structural hearth are the same size.

[egalecki]

Hey George. My oven is still in progress (slow at the moment, I have company and it's been insanely hot here), so I can't tell you how wonderfully it works, but I have 4 inches of vermicrete on top of my structural layer (I used cove base as the form, worked pretty well) and 2 inches of insblock19 on top of that. I have left my form in place for now, since it is crumbly stuff, but I'm going to take it off when the dome is finished and then run a coat of either refractory concrete or the mortar over the whole thing to sort of tie it all in before I do the blanket/vermicrete coating. So, I have 6 inches of insulation under the thing total. You can see my pictures either on my link in this post or at my thread on this site- Elizabeth's oven.

[George T]

Thanks Elizabeth. I looked at your pictures the other day. Looks good. We did get our structural layer put in today....was hot and humid here today too. I plan to do my perlite and portland tomorrow I have noticed that some just pour it where the oven floor is. seems like a lot of work to build that form. But maybe it keeps it more level?

I am a little concerned with how to really get the perlcrete good and level for the oven floor......I have wondered about putting some firebrick splits in the perlcrete like the picture in the Forno plans.....but that looks complicated too....

arghhhh....

[asudavew]

Lots of pics.

but check out my thread

I built a form and poured the perlcrete where I thought my oven would be.

[thebadger]

Unless someone knows how I think it's pretty hard to get the perlcrete "level".

Thats why I'm glad I got the FB board. I still used sand/fireclay (from cutting my bricks) to lever the board.

I know some have used thinset of HS to create a level surface.

Thanks
Dick

[asudavew]

Here's a pic of the perlcrete form...

[George T]

Thanks Guys. I have looked at lots of pictures
First the FB board seems price at an insane price if I am understanding....I have a 42 inch oven and the directions say 4 pieces....$280 plus shipping.

I bought my perlite for $54 and two bags of portland $17 or total $71. I have seen some say it was almost the same price for FB board....but I could not see it.

Asudavew....do you think building the form was worth the time? What were the advantages from your perspective.

Thanks.

[Dino_Pizza]

You've got me wondering too George. I keep reading these posts thinking why in the world would anyone want to mix concrete and vermiculite and "pour" another slab on to the one they just did when you could put the cement mixing equipment, trowels and forms away and just install 2 or 3 inches of FB board. Bu at an extra $200, I don't know. I think the FB board would save a lot of time and mixing fus and that is certainly worth something. Perhaps it depends on how easy to find and cheap the vermiculite or perlite is in your city. I'll be watching these posts to see what everyone thinks.
Good luck, my oven is still 2-3 months from starting.
Dino