Medium vs Fine grade Vermiculite?

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

I followed the rules. Oven door height is 1 inches and dome height is 16.5 inches. Oven depth is 42". Chimeny height should be at least the depth of the oven. How do we measure chimeny height? From the floor of the oven?

[Rolaed]

First Firing

Hi everyone:

Got my first big fire going today. I still do not have insulation on the outside of the dome. It was around 40 degrees Fahrenheit outside. First thing I noticed was a little smoke seeping through the seams of the dome firebrick. Is that a big deal? Should I seal them?

Also, after about a 2 hour fire, the max temperature I got was 300 degF deep inside the oven. The dome was very hot but the hearth firebrick at the entrance was warm to cool. What am I doing wrong? How does the oven floor got hot? Heat reflecting from the dome? How long does it take to get hot?

Help please.

[dmun]

Re: Medium vs Fine grade Vermiculite?

I also wonder if laying the floor bricks on their side is as smart as laying 2 layers flat. Flat presents fewer seems for heat to escape if the 2 layers are offset...

I wouldn't worry about this, floor voids fill with woodash, and also, heat rises. Do whichever appeals to you, but my two cents is that herringbone bricks on edge are a really cool look.

[thamnophis]

Re: Medium vs Fine grade Vermiculite?

Are your oven dome and walls all firebrick?

Mine are. Just the thought of breaking my 5x4 ft oven apart to "fix" it makes me break into a cold sweat :-)

I also wonder if laying the floor bricks on their side is as smart as laying 2 layers flat. Flat presents fewer seems for heat to escape if the 2 layers are offset...

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

We did the dome today. It is drying now. Question about the exterior top of the dome, should I fill it in with the same fireclay/sand/lime/cement mix OR can I get by with just sand adn cement as my mason suggested?

[Krayon]

Re: Medium vs Fine grade Vermiculite?

Ignore the amount of cement, just use the perlite cubic feet.

In your example, you need 5.34 cubic feet of perlite, and at 1-5 ratio, one bag of portland cement (a 94# portland=1 CuFt).

thanks got it. makes things easier. now i just gotta find suppliers round here in Manila, planning on medium grade for my slab and fine over my dome, if the cost isnt too prohibitive.

thanks, Ill probably be hanging around here more often from now.

[Tscarborough]

Re: Medium vs Fine grade Vermiculite?

Ignore the amount of cement, just use the perlite cubic feet.

In your example, you need 5.34 cubic feet of perlite, and at 1-5 ratio, one bag of portland cement (a 94# portland=1 CuFt).

[Krayon]

Re: Medium vs Fine grade Vermiculite?

another question regarding medium/fine - how can you estimate how much perlite should you use in making the insulating percrete? let's say a 4' X 4' X 4". Any different from estimating normal concrete?

[Tscarborough]

Re: Medium vs Fine grade Vermiculite?

You are right, I got cornfused. I sell the bucket for 22.50 and the 55# bag for $55.00.

[dmun]

Re: Medium vs Fine grade Vermiculite?

Heatstop is in the 40-60 dollar range for a 1 gallon tub of dry. If they are selling it for 14 bucks, something is wrong.

Heatstop comes (or did when I was buying it) in a ten pound plastic tub, and a 50 pound bag, where it's called heatstop50. It goes from a little more to a little less than a buck a pound, so fourteen dollars for a bucket is about right. The fifty pound bag is in the fifty dollar range.

It will take three to four fifty pound bags of heatstop if you aren't cutting bricks to angles. I built my 36 inch thin dome with one bag, but I cut every joint.

[Tscarborough]

Re: Medium vs Fine grade Vermiculite?

Heatstop is in the 40-60 dollar range for a 1 gallon tub of dry. If they are selling it for 14 bucks, something is wrong.

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

Refractory cement is different than refractory mortar. As far as refractory mortars go, most FB'ers recommend the dry mix, instead of the wet stuff that comes in tubs and is prohibitively expensive. The first five or six places I called looking for Heatstop 50 didn't carry it anymore so I called the corp office back east. I was quoted $85 for a 50lb bag (without shipping) by a lady whose nasty tone of voice told me she had better things to do than talk to me. I am now building my oven with homebrew mortar, but you can always order an 'authentic' refractory mortar from James here on the FB site.

The stuff at the builders supply place is called HeatStop and it is a powder. They charge $14/gallon. Is this the stuff to use? How many gallon tubs would I need to buy?

[dmun]

Re: Medium vs Fine grade Vermiculite?

Refractory cement is not sold by the gallon. It's a powder, and it's sold by the pound. You probably don't want it anyway: calcium aluminate mortars are difficult to work with. What your vendor probably has is pre-mixed wet mortar in tubs. It's not cheap, and it has problems for our application: it's heat set, it's not water resistant, and it's designed for minimal joints, unlike the wedges between tilted bricks that we need to build. When you lay it on thick, it has real difficulties drying.

Besides, why pay refractory material prices for water? Have you looked into the homebrew mortar? It's inexpensive, and builders have had good results with it.

If your refractory dealer doesn't know what fireclay is, I'd wonder what else he doesn't know. Southeast Michigan is the mecca and medina of American industry. A google maps search for "refractory near canton mi" returned 188 results. This is to say nothing of the brickyards and mason suppliers that will sell fireclay for half the price.

As to your vermiculite question: you can build on it as soon as it is solidified. One of our builders just set down his floor in the wet vermicrete: no waiting at all. Also, covering it and building onward is as good a way of keeping it damp for a week an any.

[GianniFocaccia]

Re: Medium vs Fine grade Vermiculite?

Refractory cement is different than refractory mortar. As far as refractory mortars go, most FB'ers recommend the dry mix, instead of the wet stuff that comes in tubs and is prohibitively expensive. The first five or six places I called looking for Heatstop 50 didn't carry it anymore so I called the corp office back east. I was quoted $85 for a 50lb bag (without shipping) by a lady whose nasty tone of voice told me she had better things to do than talk to me. I am now building my oven with homebrew mortar, but you can always order an 'authentic' refractory mortar from James here on the FB site.

[Rolaed]

Re: Medium vs Fine grade Vermiculite?

I poured the 4" vermiculite/portland cement mixture today. Strange spongy stuff!! You cant really level it like concrete. A few bumps/waves here and there.

Do I need to put plastic over it or water it periodically? If so, how often.

How long should I wait before laying the firebrick.

Also, is refractory cement the same as fireclay. The place I got the vermiculite from sells refractory cement by the gallon. How many gallons would I need?? It is not cheap!!