Continued Design Ideas

[SCChris]

Re: Continued Design Ideas

The mass of the concrete will temper things a bit, as long as the temps aren't sustained and sub-freezing wind aren't an issue.. You might think about throwing a few old blankets or comforters over the pour and heat from below.. Anyway, keep your fingers crossed for a few days of appropriate temps.

Chris

[SCChris]

Re: Continued Design Ideas

Hey Craig, Think about getting the slab warm before you pour. It wouldn't take much to get a tarp plus some blankets over things and then put a bare bulb in the wood storage area/s. The structure should heat a bit before your pour. Are you pouring tomorrow?

Chris

[clofgreen]

Re: Continued Design Ideas

Was hoping to pour tomorrow but the latest report shows snow starting later today with 1 - 3 inches expected in my back yard. No time to set up a tarp and warm the slab. Looks like I'll have to wait. But thanks for your reply.

Craig

[SCChris]

Re: Continued Design Ideas

Best to you!

C

[clofgreen]

Re: Continued Design Ideas

Today was to be the last day before another storm moves in so I took half a day off work and poured my perlcrete hearth. It was fairly easy thanks to the great instructions on this forum. I did things a bit different though so I thought I'd document them. As I thought about the insulation slab it occurred to me that the place that needs the most insulation is right under the oven floor. Conversely, at the edges where the weight of the vault, vent and chimney comes down on the perlcrete it needs to be stronger but doesn't need so much insulation. So first I mixed a batch of 5:1 perlcrete and lined the edges, packing it down fairly solid by hand. I figured this is where it needed to be strongest to hold everything in. Here's a picture of the first layer. I added several more layers of 5:1.



Next I added several batches of 6:1 and hand packed just until firm. Finally, I added 10:1 under the oven floor, hand tamping very lightly. After I screeded the slab I topped it with a thin 5:1 final coat and tamped it lightly with a moistened trowel to flatten and consolidate the surface.

Here's how I mixed the 6:1 perlcrete. Using a number 10 tin can I measured four cans of portland cement into a five gallon bucket making it about 2/3 full. Next I measured 24 cans of perlite into a wheelbarrow, added four cans of water and mixed. Next I added water to the cement until the water was three inches from the top of the bucket. I mixed it using a drill and paint mixer attachment. This made just over half a bucket of cement slurry that had the consistency of thick syrup. I poured this into the wheelbarrow and gently mixed with a shovel until all the perlite was coated. This made a fairly dry mix but was just moist enough to hold together. I filtered this through a screen made out of hardware cloth (the kind used to screen rocks out of garden soil). Sifting it this way allowed me to filter out and break up any cement clods giving it a nice uniform mix.



To keep snow off, I built a makeshift shelter out of an old fence I tore down.



To keep the perlcrete warm while it cures, I clamped a heat lamp inside the shelter and covered it with a tarp. I plan to let it cure a week.

Craig

[SCChris]

Re: Continued Design Ideas

Looking good Craig.. Let us know how the curing comes along using the tarp and lamp.
Since you're up there in altitude and winter storms are starting to push through, I'll keep my fingers crossed for a bit of warmer weather without to much wind to steel the heat of your build.

Chris

[Derkp]

Re: Continued Design Ideas

Craig,

It's coming along. For my slab I poured it 8" thick with a framed in depression 4 inches deep directly under the oven, leaving a full thickness of concrete to support the oven arches, the opening arches and the back wall of the oven. The depression was filled in with percrete, leveled with a little sand and our super duper "Geneva Steel" leftover firebrick floor on top of that. It seems to work well. Our floor is made up of a comnbination of 6X4.5X18 inch 3000degree firebrick.

Derk

[clofgreen]

Re: Continued Design Ideas

Chris,

The tarp wrapped around the shelter and heat lamp has done well. On cold frosty mornings the temp stays right at 50 and during the day when the outside temp gets up to into the forties, the temp goes up to 60 - 65. The perlcrete has cured very well, hard and solid with only a few loose granuals on the surface. This is a 6 inch perlcrete slab so I'm hoping it will insulate properly and not make me regret not splurging on insul board. But at 10:1 under the oven floor it shouldn't (crossing fingers).

Derk

I've been watching for posts from you praying I won't read the words, "firebrick is cracking." I read a post where someone had bought firebricks that had been left outside and the freeze thaw had weakened them. Don't know how many freeze thaw cycles our bricks have gone through but am guessing given the amount of coal dust on the piles its been quite a few. I've also read that these super duper high temp bricks are intended for constant high temp firing and that they are more suseptable to cracking when heated and cooled many times. Again, crossing fingers that they'll hold up. Still hoping to get up to see your build but an already busy life has been made more so by trying to get this oven built.

Craig

[Derkp]

Re: Continued Design Ideas

Craig,

No problems with the bricks. They sure were very dirty when I got them too. I had to buy a few 1/2 firebricks from Bhuener(sp?) block downtown and our bricks are in a whole different league. They seem to be much harder. Just don't drop them, they chip easily.

Derk

[clofgreen]

Re: Continued Design Ideas

Hey Derk,

I just found out that you are a beekeeper. My father-in-law has been one for thirty five years. He had THE prime spot at the Pioneer Park Farmers Market until a couple of years ago when he retired. He still has a couple of hives in his back yard though. What's the name of your business and where do you sell your honey? You might be interested in this report:

Tests Show Most Store Honey Isn't Honey

Craig

[clofgreen]

Re: Continued Design Ideas

I have several questions about the landing and opening dimensions specifically as it relates to oven size, fire performance and venting efficiency.

Here's an ortho of the landing.



And an elevation.



And now the dimensions.



The oven floor is 30" wide x 40" deep and the vault is 17" high. The 10.5 inch oven opening is 62% of the oven height.

Now the questions.

1. Given my oven dimensions, do you think a 17" opening is wide enough? Are there any fire/venting performance issues caused by this opening dimension?

2. I've made the brick opening 3/4" lower than the oven opening. Is this enough difference to forch the smoke up into the vent and not out the opening? The top of flue is 3 feet above the vent opening.

I'm starting to cut firebricks so I would greatly appreciate your response. Thanks in advance.

Craig

[Tscarborough]

Re: Continued Design Ideas

The outer opening needs to be bigger than the inner opening or you will be making a 2 part door or a very awkward insertion.

[clofgreen]

Re: Continued Design Ideas

Thanks TS! I hadn't even considered a door. Your response prompted me to design one and to learn how to do an animated GIF.



I'm thinking of casting it out of perlcrete with wooden handles connected by embedded bolts somehow.



Craig

[brickie in oz]

Re: Continued Design Ideas

I'm thinking of casting it out of perlcrete with wooden handles connected by embedded bolts somehow.

It wouldnt last 5 minutes, it would fall apart.

[clofgreen]

Re: Continued Design Ideas

It wouldnt last 5 minutes, it would fall apart.

Ah, yes, Perlcrete is good in compression, not tension. Wait, metals are good in tension. Maybe I'll cast the perlcrete then dip it in a vat of molten steel. Now I'll just have to go find a vat of molten steel, unless someone has already figured out a good door recipe.

Thanks Brickie.