Using Quikrete instead of Portland?

[JRDeMeo]

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]

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]

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]

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]

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]

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?

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

What was your mix ratio of quikrete to vermiculite?

[JRDeMeo]

Re: Using Quikrete instead of Portland?

I used 72 cups (18 4 cup scoops) to one 90lb bag.

[adman2u]

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]

Re: Using Quikrete instead of Portland?

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]

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

[dmun]

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.

This has been tried and tried again with the same results. If you are baking bread you might, just, get away with a firebrick on masonry or rubble/sand/glass/gravel layer, if you have unlimited time and wood.

But for pizza, we really need that floor to be hot, and to stay hot. It can only be recharged by the radiant heat, so we need thermal isolation under that floor, or the heat will be sucked away.

Insulation isn't free, but neither is fuel, even if you cut it yourself. There really isn't any reason not to insulate under the floor.

[james]

Re: Using Quikrete instead of Portland?

You don't need to take anything out -- you can always add an insulating layer above what you have; either 4" of vermiculite concrete or 2" FB Board. Either way, I think it is worth the little bit of extra work and cost to make sure your oven really performs well. You'll be happy you did it when you are cooking.
James

[Breven]

Re: Using Quikrete instead of Portland?

JR-

Download the instructions on how to build an oven from this site. Follow them. Though there are many adjustments that can be made to suit your needs, the basics are covered. I literally printed the instructions, along with pictures of oven progress from people on the site and just did what they did.
The mixing of Concrete rather than cement & vermiculite might be the first of many problems you can avoid. For us novices- best to follow the lead of the experts.

[adman2u]

Re: Using Quikrete instead of Portland?

Interesting but I'm done so modification is not happening. I have six inches of solid concrete on the ground not suspended like many ovens. Then a layer of firebrick thats about 3 inches. I have at least 9 inches of masonry on bottom - our soil is pretty much sand.
The top is firebrick and parged with insullation about 6-8 inches total a layer of cardboard for expansion and then poured solid up to 18 inches.
What do you think I can expect in charging and how long do you think my heat will stay hot? I never had an oven before. You can see some pictures in photo gallery look adman2u. I have not baked any bread or pizza yet.

[adman2u]

Re: Using Quikrete instead of Portland?

sorry I'm new here I sent reply but its posted below - would like your comment