? crack resistant, Vemic,& Perlite differences
(M) The Forno Bravo Step by Step directions advise using "Quickcrete Crack Resistant Concrete" as the top thermal layer in the Insulating Hearth. Locally that brand is not stocked, however I can buy concrete with fiberglass fibers included. The Mfg. is "Ross Island" and I believe they call it fiber reinforced. Is this essentially the same product? ____
(M) Please confirm that "crack resistant concrete" (rock aggragate included) is indeed what is called for, (rather than crack resistant mortar). ____
(M) For that Insulating Hearth, the first layer recommendation is for either Vermiculite or Perlite. Locally, the Vermiculite is marginally more expensive but not enough to disuade me from using it over the Perlite if there is any insulating, or adhesive advantage of using it.
(M) If you know of the relative insulating properties of both, would you please make a recommendation? ____
i used perlite, as it was cheaper and was what was easily available. i did some research, and found R-values on the web, but don't know them off the top of my head. seems comparable though.
the crack resistant concrete is the one with the fiberglass fibers in it. for what its worth, i found that the fibers make it difficult to "work" the concrete (e.g. smooth the top and insure filling of voids). i think the crack resistance might be overkill given the amount of rebar in the hearth. if you plan to have exposed concrete, you might consider using the plain vanilla stuff.
i used both vermiculite and perlite and i preferred the perliete because, unlike the vermiculite, its a different color (white) than cement and it was easier to visually see that you had the cement throughly mixed into the perlite. also it seems to be easier to work with.
2 Gurus recommend perlite
Dear Paul, and Robert,
(M) Thanks to both of you for your views on Perlite v/s Vermiculite. I will go with the Perlite since both of you have successfully done so.
(M) Robert, you wrote in part: "if you plan to have exposed concrete, you might consider using the plain vanilla stuff."
(M) I plan on building a roof for my igloo, as does Paul. Since my Insulating Hearth Slab will not be visible, I'm not concerned with the smoothness. Also, the PSI of the crack resistant concrete is 5,000 so for about $30 extra, I can afford to "over-do or don't do it" ;-)
(M) I'm off to Home Depot as my "Jerry's" doesn't carry "the hot set-up" concrete.
If you have time, especially Robert since you have something of an outdoor kitchen, could you visit this Forum's:
OVEN MANAGEMENT/Heat Management/What ideas do you have about an adjacent pit BBQ?
If you have some ideas, let me know please. Thanks.
i wish i had space to include a grill/bbq pit in my design, but as you can see from this birdseye view of my backyard, i don't have much space left...
(oven at bottom left)
i had thought of using the shelf space to the left of my door for a small grill, but i think i'd rather have the counter space.
with your slab as large as it is, i would certainly include one! as for the design...well, the possibilities are endless...
BTW, no diff between vermiculite & perlite except in trading potential difficiencies. Vermiculite can be contaminated with trace amounts of asbestos (commonly found where vermiculite is). A dust mask is recommended when working with the loose fill. No issue once it's entrained in cement. Perlite can be coated with silicone to make it slide easily into block cores (where it's commonly used to insulate block walls). You need to make sure it's horticultural grade perlite rather then the construction additive. The insulative properties are near identical.
Horticultural not construction grade perlite is important!
Jim, you wrote, in part:
(J) "You need to make sure it's horticultural grade perlite rather then the construction additive. The insulative properties are near identical."
(M) This seems like a very important bit of information. Do you think you'd like to talk to James about adding it to his otherwise highly comprehensive directions?
(M) I was fortunate and lucky in that I purchased the Horticultural grade, without silicon. I bought 16 Cu/Ft. which I'm sure is way more than I need for the insulating Hearth Slab, but it won't go to waste as I can store the extra for use under the oven roof, one day. I also bought two 94 Lb. bags of cement. My initial calculations for a 6'x6' x 2" underlayer suggested that one bag would suffice in James ratio of 6 parts Perlite to 1 of cement, but then I got nervous at Home Depot. I'm getting someone with a small electric mixer to help me with the slab pour tomorrow and Home Depot is over an hour round trip; by the time I got back the insulating layer might start to dry and harden.
(M) Paul, I can see from your great photo that you don't have room for a full outdoor kitchen. How did you manage to post 186.36 KB when I am limited to 97 KB. Are you a personal friend of James ;-)
my photos are all "<IMG>" style links that pull the picture up from another website when you open the thread...kind of like jim's photo album on yahoo, but photobucket is designed to host photos online easily.
no room for an outdoor kitchen, but then again, my indoor kitchen is only 10 ft. away. (the house roof is at the bottom of the picture)
by the way, the barn structure you see, and the greenhouse are two of the main reasons i haven't got to the vent and roof yet. too much to do...gotta hurry before the rain comes!!!!
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