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how about comparing FB board to vermiculite/perlite for the insulating hearth. i am concerned about the compressive strength of vermiculite/perlite - portland cement mixture. seems like there's a good bit a weight to support. I don't know too much about either of the products so any input would be greatly appreciated. thanks, rino
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Re: FB Board versus vermiculite/perlite
I don't have scientific numbers for you, but my oven is sitting on a 4 inch layer of vermiculite concrete right now. I made a form for the vermicrete and it's not surrounded by regular concrete or anything, just on it's own. It's very strong in compression although it seems kinda crumbly to look at it. It hasn't moved or compressed at all as far as I can tell. I also have a layer of insblock 19 (couldn't swing the shipping on FB board) on top of that- neither product has budged. -
Re: FB Board versus vermiculite/perlite
WOW!!!!
Looking real good... your photo's are inspiring to keep the project on track.
Elizabeth... can you touch on the following for me...
I noticed that you've limited the Vermiculite hearth just underneath the oven floor... I wish I had thought of that... That being said, you also seem to have, and have stated in your below comment that you used "INSBLOCK 19"...
Can you tell me a little bit more about this product:
1) What function does it have
2) Where do you purchase it
3) What is it's cost
Dome looks Excellent"
1) Did you cover the dome with a layer of High Heat Mortar and if so how much...
2) Did you use Forms or did you create freehand
3) How did you get the height of your dome to the plans specs
4) Is your first string of FireBrick MORTARED onto the oven floor or loose
Thanks.Comment
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Re: FB Board versus vermiculite/perlite
Insblock 19 is a Harbison-Walker product. It comes in 12" by 48" (I think...) sheets. I think it may come in different thicknesses, but mine is 2". You have to buy a whole box of it, so I have leftovers, but I'm using it in my door as well. I had originally planned to do 2 layers of it, but with the 4" of vermicrete and the 2" of insblock, I decided that was enough! It was getting a bit too thick, and I'm not very tall. I got mine in the nearby big city at the rep for H-W. There's a website you can look on for a rep near you. I can't remember what mine cost right now- I think it was in the neighborhood of 150 for the box, but don't quote me on it.
I did coat my dome with a thin layer of mortar, which was the homebrew recipe. I didn't use much, just about 1/4 to 1/2 inch, and that was only to dress it up and fill in my rather large in places external gaps. I used heatstop50 for the rest of the mortar, but I think the homebrew would have worked fine.
I did my bricks freehand, mostly. I used a variation of Ken's string (see his thread, my old kentucky dome) to get the right curve going and to keep it round. I used sticks to keep my bricks up on the last several courses- but really, when you make the mortar sticky they don't need much for long. I wouldn't bother with forms. By the time you get to the point you need to defy gravity, you'll have the hang of the mortar and be fine.
Once you see what the spacing is on the outside of the bricks, you can keep it going pretty easily even without the string... I stopped using it when I got closer to the top. I also made the last three or four rounds with 1/3 bricks instead of 1/2 bricks because they fit better. (this will make you have a slightly lower area on the outside there, and I filled it up with the homebrew to make it even)
I made a dry run on paper first- took the measurement across the floor, added the measurement for the height, and then fit the bricks to it on my deck. I used that for reference to be sure how far from the center each course should be as I went and to get the outside angle formed by the bricks. I think there's a picture of that on my thread...
My soldier course sits on top of the floor and is NOT mortared to the floor, but the bricks are mortared to each other. I used strips of newspaper to keep them from sticking to the floor.
Just get started! It's not brain surgery. If it looks ok, it probably is ok. Mine's not beautiful, but it works just fine. Just make sure you keep cleaning off the inside surface as you go, or you'll have a nasty mess to clean off. Use a damp sponge as needed to clean it up. I did it at the end of each round.Comment
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Re: FB Board versus vermiculite/perlite
Ok, I correct myself. The insulation boards are 12 by 36.
Here's the picture of the dry run cross-section I did. Keep track of how far each course is from the center pin and measure the outside edge gap and you're golden for the correct height!Comment
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Re: FB Board versus vermiculite/perlite
FB Board is 24"x36"x2".
JamesComment
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Re: FB Board versus vermiculite/perlite
Hi elizabeth,
Contacted Harbison-Walker,
Quick qestion... did you speak to someone who recomended INSBLOK-19 rather than INSBOARD products? Also where did you get the Blanket for the dome?Comment
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Re: FB Board versus vermiculite/perlite
It's been a while- I don't remember, to tell you the truth. I think I may have already decided what I wanted to use when I called.
Forno Bravo's board is great stuff, James, I just couldn't swing the shipping to VA from CA for two of your products. I chose to put it into using Forno Bravo's fabulous blanket instead. 2 boxes worth and it was worth every penny. Easy to use (although a bit messy, wear gloves and a mask) and not too heavy for me to do on my own.Comment
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Re: FB Board versus vermiculite/perlite
Yeah...
I have the same concern being in NY. I'd love to go through Forno Bravo and will on the Blanket for sure... truthfully I haven't decided on the boards as of yet as I'm banking on the 4" of Vermiculite Slab. Your above description of cooking after 3 Days with the initial firing is very appealing. If someone could confirm that the same is possible with just the 4" Vermiculite I'd be a happy campe.Comment
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Re: FB Board versus vermiculite/perlite
4 inches will be fine.Originally posted by delay!fox View Post
But more is better.
I have about 3.75 inches of vermiculite plus a half inch of high heat mortar on top of that. Followed by the hearth bricks.
My oven performs very well.
If you can swing it though, go for the forno bravo boards.
My 2 cents.
Dave
P.S. You have become obsessed. Haven't you?
Don't worry! It's natural. Your spouse will think you are crazy.. so will the kids... your friends... your neighbors.. and even your dog
But they will understand when they eat the pizza.
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Re: FB Board versus vermiculite/perlite
I used insblock19 because it was considerably cheaper than cal-sil boards at the time. I priced it from my local H-W dealer, but I got it cheaper from an internet supplier. You do have to buy the whole box, which gives you one board more than you need. Mine was 2.5 inches thick, which may be non-standard, and why I got it at a cheap price.
Insblock19 works fine. My support slab barely gets warm at full fire. My project stopped in the middle for the winter, and the insblock got damp repeatedly, with no compression problems.Comment
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