vermiculite to portland cement

[mrgweeto]

Re: vermiculite to portland cement

Bob,
I actually found Griffin Greenhouse supply in Cheshire. I got it from a friend that owns a florist business. They sell fine, medium and coarse vermiculite for $22.18 per 6 cuft bag. May want to give them a call when and if you need anymore for the dome. Good to know about New Haven Masonry. Their prices for firebrick are good I thought. $1.25 each. Good thought on the extra portland. Your pour looks good.
G

[david s]

Re: vermiculite to portland cement

The lesser proportion of cement to vermiculite results in better insulation but weaker strength. Since strength is not really an issue in the insulating layer then the cement content is there to hold the material together. I found a 10:1:3 (by volume) of vermiculite,cement, water works well. The correct amount of water is important otherwise a mix of too much water will draw away the cement into a watery slurry and leave vermiculite uncoated with cement. Also don't compress the mixture when applying it. This will only reduce its insulating value. Tapping with the flat of a trowel works well.

[pizza_bob]

Re: vermiculite to portland cement

David,
I went with a 5:1 mix because under the vermicrete layer I had 2.5" of Foamglas. The insulation performance of the Foamglas should be superior to the vermicrete but this is my first oven so I can't say for sure. I'm hoping the 2.5" of Foamglas will provide nearly the same insulation performance of 4" of vermcrete. Then the 5:1 vermicrete ratio can provide me with a some thermal mass but not too much. I've been attempting to figure out this balancing act of insulation vs. thermal mass. The oven will be used for pizzas 90% of the time but I was concerned that minimal thermal mass would not allow me to do 8 or 10 or 12 pizzas without pulling the coals back over to recharge the hearth.
I start laying my cooking hearth this weekend.

As far as getting a uniform distribution of Portland throughout the cement...I used a paint mixer attached to a drill and mixed the Portland and water together in a bucket until it became a slurry. Then I dumped that slurry into moist vermiculite and then added water until the correct consistency. I thought it worked really well...

Regards,
Bob

[david s]

Re: vermiculite to portland cement

Sounds good Bob, but if you are wanting more thermal mass then it should be added under the insulation not over it.

[pizza_bob]

Re: vermiculite to portland cement

Sounds good Bob, but if you are wanting more thermal mass then it should be added under the insulation not over it.

David,

Wouldn't that defeat the whole purpose of the thermal mass? Insulation is to keep the heat in. If you have thermal mass under "perfect" insulation then heat would never reach the thermal mass. I understand the insulation used for pizza ovens isn't "perfect" but the concept doesn't change.
If built by FornoBravo plans... the 3.5" layer of concrete that is under the vermicrete layer is not for thermal mass. It's for structural purposes and the thermal mass in these designs are the cooking hearth bricks.
That's how I believe this works but I could be wrong.

~Bob

[Lars]

Re: vermiculite to portland cement

Bob,
I agree, but I didn't really want to chime in until I was sure I hadn't missed something in your particular build. Also, I really think mixing the concepts of 'thermal mass' and 'insulation layer' just muddies the waters. The vermiculite layer is for insulation. The more portland you add, the, slightly, less insulating properties it has, perhaps. As far as adding thermal mass, if you really wanted to do that, then set your oven bricks on the 2.5" side and use 4.5" thick oven floor. Or build up a layer of 'fireclay mortar' one inch thick under the entire oven floor brick layer.

Personally, it's hard to know exactly how this will all perform. I ended up with a very thin layer of vermiculite under my floor. (2.5") I am crossing my fingers that the oven will still heat up and make pizza's well enough. I have a feeling I may have to throw in an extra log here and there, but, oh well. Without several firings, it will be hard to speak with any authority on the matter.

Lars.

[mfiore]

Re: vermiculite to portland cement

I think there may be a misunderstanding using "under" and "over", since the insulating layer is both underneath the oven and surrounding the dome.

To clarify, which I think you both intend to state, the insulation should surround all thermal mass. On top of the dome, it is above. Under the hearth, it is under, any extra thermal mass.

[mrgweeto]

Re: vermiculite to portland cement

Well...Did our vermiculite/portland hearth tonight. It came out rather well. Because we did it in a wheel barrel we took a 1 gallon pail of cement to 5 of verm. to 1. 5 gallons of water. Mixing with a garden rake well first and then addin gthe water gave us a very good consistancy. We then shoveled it into the form and skreet it the best one can with the material that was like moist oatmeal. We took our flat steel trowel and pat it down. I can see how it gets its insulating quality. It has nice feel to it. We plan on starting the floor at the ens of the week if not then Sun is the day.
Bob, where have you found the fire clay and mesh sand? I assume mesh sand is just fine sand. Does anyone know why we couldn't use a slurry of refratory and sand in place of the fire clay. Any thoughts or substitutions?
G

[Lars]

Re: vermiculite to portland cement

Hey Mike,
What did you decide about your cracked flue?


G.
You can buy extremely fine sand at most Lowe's type stores. The fireclay is available at most pottery and clay working places. I ended up using refractory mortar, but I would have used fireclay had I known better ( the particular mortar I used was not that great -- but I am sure it will be fine... essentially, it's just to level the bricks) by the time you build an igloo on top of them, they will likely stay in place without any mortar. Isn't that vermiculite mixture cool?

Good luck.

Lars.

[mfiore]

Re: vermiculite to portland cement

Hey Mike,
What did you decide about your cracked flue?

Still scratching my head.

[david s]

Re: vermiculite to portland cement

Bob'
Sorry I thought you were talking about adding the thermal mass over the ,insulation on the dome.
David

[mrgweeto]

Re: vermiculite to portland cement

Lars,
I will probably end up using the refractory cement and possibly adding a little sand to it. It's amazing that there are so few pottery/ceramic supply houses in our area. I too think that the primary purpose is to act as a leveling agent. I will end up with a little more than a 3" inch insulation hearth. I think that will be just fine. there is a couple around the block that built a pizza oven without refering to any plans and not having any knowledge that is afforded now and don't even think that they have an insulation hearth and they are using their oven effectively. I don't think that they have the high extended temps that we should achieve with our ovens but the bottom line is they are having a ball making pizzas for themselves, family and friends on a regular basis.
Will start the floor and dome this weekend, that's where the fun and swearing will start. Looking forward to it.Thanks for the info.
G

[Lars]

Re: vermiculite to portland cement

G.
In Connecticuit? Wow, I would think there would be MANY people doing clay, and several sources for fireclay. My first bag was hard to come by ( someone actually drove it up from KS ( 3 hrs.)) but later I found a quick source, and later yet another.

If you plan to mix your own mortar you will need about 90 lbs. I thought that I could not find it here when I first started looking, but I was surprised to find those several other places, and even a less expensive source for firebrick, ceramic blanket, etc. months after I first started looking.

Good luck.

L.

[mrgweeto]

Re: vermiculite to portland cement

Thanks a lot Lars. I think I am going to use refractory cement and mix it loose to use as a leveling/bonding agent. I may call a few art stores in the area to see about the fireclay.
G

[pizza_bob]

Re: vermiculite to portland cement

G-
In regards to your fireclay. I just posted this on my oven build thread.

http://www.fornobravo.com/forum/8/pizza-bobs-42-build-7155-2.html