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JRDeMeo 08-06-2008 05:25 PM

Using Quikrete instead of Portland?
 
Is there a difference in using Quikrete instead of Portland? I plan on using Quikrete for all my insulating because I have a lot left over from my foundation. Will this give me enough strength?

james 08-06-2008 05:28 PM

Re: Using Quikrete instead of Portland?
 
Quikrete is concrete -- a mix of Portland cement, sand and gravel (and a setting accelerator). But for your vermiculite concrete you want to use pure Portland cement (not concrete). Think of it this way -- when you make insulating concrete, vermiculite replaces the sand and gravel as the aggregate that you mix with Portland cement.

You can buy Portland cement by the bag at Home Depot and it isn't expensive.
James

dmun 08-06-2008 05:41 PM

Re: Using Quikrete instead of Portland?
 
You will have lots of uses for your unused concrete mix (if that's what it is, they make several mixes) in this project. Vermiculite/perlite concrete needs portland.

JRDeMeo 08-07-2008 07:55 AM

Re: Using Quikrete instead of Portland?
 
Ok so here is my next question...how bad is it if I already layed my insulating layer with quikrete? Is it going to hold the weight of my dome? Do I have to break it down and pour it with portland?

Faz 08-11-2008 06:44 AM

Re: Using Quikrete instead of Portland?
 
The concern is that the presence of aggregate in the mix (assuming that it is a dry concrete mix rather than just a fast setting cement) will greatly reduce the insulating properties of the layer. If this is the case you can either remove and relay or maybe add a further insulating layer over the top, as long as that wouldn't make your oven too high.

asudavew 08-11-2008 07:30 AM

Re: Using Quikrete instead of Portland?
 
Quote:

Originally Posted by JRDeMeo (Post 38535)
Ok so here is my next question...how bad is it if I already layed my insulating layer with quikrete? Is it going to hold the weight of my dome? Do I have to break it down and pour it with portland?

It's bad.
Most heat is lost through the floor.

What was your mix ratio of quikrete to vermiculite?

JRDeMeo 08-11-2008 09:25 AM

Re: Using Quikrete instead of Portland?
 
I used 72 cups (18 4 cup scoops) to one 90lb bag.

adman2u 08-11-2008 10:05 AM

Re: Using Quikrete instead of Portland?
 
At my home depot they sell ALL of the broken bags of concrete products for $4.10 - I do mean all - if they have six broken bags its just $4.10 TOTAL I used stucco on the outside of my last cooker and got two bags plus seven quick crete for $4.10 That stuff is $17 per here in FL. - what a bonus if you have a way to transport.

asudavew 08-11-2008 10:24 AM

Re: Using Quikrete instead of Portland?
 
Quote:

Originally Posted by JRDeMeo (Post 38725)
I used 72 cups (18 4 cup scoops) to one 90lb bag.

I know you will hate to hear this.. but I think you need to redo it. Or form another insulating layer on top. I think what you have now will simply wick your heat out. And your firing times will be long, and your wood consumption will be high. It will cost you in the end.


The insulating layer should be 5 parts verm to 1 part Portland cement and just enough water to hold it all together. Mix the dry ingredients first, then slowly add water until you can just squeeze a little water out the mixture with a closed fist.


I have a 3.5 - 4 inch layer of the vermcrete under my oven, and I wish I would have built it up to 6 inches or more.

Just my opinion, but I'd hate to see you build an oven that is hard to use, under cooks the bottoms of your pizzas, and burns the tops.


Let us know what you do.

Dave

adman2u 08-11-2008 10:35 AM

Re: Using Quikrete instead of Portland?
 
While I am new to this site I am not new to the heat and insullation concept. Heat rises! I think that a firebrick bottom with any form of concrete base should work if the top is thick enough. The purpose of curved oven tops and in a fire place angled sides is to radiate heat. My own oven / smoker / grill has seven inches of foundation then firebrick on the bottom. I used full firebricks for the box with 4 or 5 inches of cement / vermiculite a layer of cardboard for expansion then solid concrete. My weakest link is I have an actual flue thats 13 X 17 for heat to escape. I have a way to neck that down or close it with firebrick. In about a month I will be able to try the oven. It is new and I don't want to crack anmything. Plus it is to hot outside (FL) Pictures posted yesterday


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