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cheezer 08-05-2013 12:28 PM

remove the plywood support?
 
HI, I started my 32 x 36 Alan Scott type oven a couple of months ago and all has gone well for the most part. I built a substantial support to support the hearth slab poor not thinking I would have to remove it. I assumed that the 4" firebrick plus 3-1/2" slab plus 2-1/2" of vermiculite/ Portland the plywood under would be OK and I could leave it in place. I did my first fire a couple of day's ago and wow, this plywood is hot! What are the opinions as far as removing the plywood and supports and any idea's for additional insulation I could put under there?

thickstrings 08-06-2013 10:17 AM

Re: remove the plywood support?
 
It would appear that you will be losing a lot of heat through the floor based on what you said..... Is the V-crete dry? I believe 4" is recomended .Can you pick up the inside floor of your oven? Insulation is needed...Even if you went underneath and cut out the plywood ...will the plywood still be between the stand and the base? Pictures?

cheezer 08-06-2013 10:48 AM

Re: remove the plywood support?
 
Hi Thick,
Yes I can remove the plywood and 2 x 4's supporting it. The plywood is inside the block walls and the 5/8 rebar (resting on the block) will hold up the oven(so i'm told although it seems like about a billion lbs in brick, concrete, ect). All of the v-crete, and slab should be plenty dry, it's been weeks since that step. i'm pretty sure the v crete was only about 2-1/2" thick. i'll try to get some pic's posted.

mrchipster 08-06-2013 10:50 AM

Re: remove the plywood support?
 
Welcome to the high heat loss of an Alan Scott design. Is the order of your layers as you describe with the vermicrete directly on top of your plywood?

If so, removing the plywood will most likely cause the vermicrete to fall down.

If the concrete layer is against the ply And vermicrete over the concrete you should be able to score the plywood with a skill saw and pull it out in small pieces.

Ther is a huge amount of water that needs to leave the oven and it is very possible you have significant water in your vermicrete. How hot is the plywood? In real temp.

cheezer 08-06-2013 11:10 AM

Re: remove the plywood support?
 
mrChipster
Is the order of your layers as you describe with the vermicrete directly on top of your plywood?
Yes the order (bottom up) is 3/4" plywood / 6-1 vermiculite Portland mix/ 3-1/2" concrete slab / firebrick on edge. I don't know the real temp of the plywood but it was hottest in the center. I was able to hold my palm on it so I would guess less than 150 F???

mrchipster 08-06-2013 11:41 AM

Re: remove the plywood support?
 
I hope you have a great source of free wood and a place to store it. You will be going through a lot of it to heat up the oven. If you are a baker you will be able to do multiple batches of bread before the residual heat dies out. Getting to pizza temps for your floor 700+ will take several hours of high heat firing.

It is unlikely that the plywood will burn with that much material between it and the fire. Wood needs to reach 451 f to burn and that would be under ideal conditions.

I think you still have water in your slab and it will take some time for it to leave. Remember concrete does not fully cure for 30 days or longer and the vermicrete is like spongy concrete. More like wood, and wood can take 2 years to dry at ambient temps. Obviously heat speeds this cycle.

cheezer 08-07-2013 07:00 AM

Re: remove the plywood support?
 
Chip,
The comment about water in the vermiculite is baffleing, are you suggesting that as this water leaves the slab layers then the "mass" will insulate better therefore not as much heat escaping down to the plywood layer? I am considering leaving all in place and adding some micore mineral fiber board (used under hearths, ect) under the plywood then maybe some rockwool fiberbatts then another piece of ply to hold all of that up? any thoughts on that idea?

Dave

mrchipster 08-07-2013 07:46 AM

Re: remove the plywood support?
 
Quote:

Originally Posted by cheezer (Post 158928)
Chip,
The comment about water in the vermiculite is baffleing, are you suggesting that as this water leaves the slab layers then the "mass" will insulate better therefore not as much heat escaping down to the plywood layer? I am considering leaving all in place and adding some micore mineral fiber board (used under hearths, ect) under the plywood then maybe some rockwool fiberbatts then another piece of ply to hold all of that up? any thoughts on that idea?

Dave

Yes as it dries out it will heat up better, transfer less heat to the outside(I think you are creating steam right now.) and retain heat better.

Before you go to the trouble of insulating more see how the oven does after a month or so of good hot long fires. It will dry out and at that point you can decide if you need more insulation.

Adding it now would just slow the drying process, you have a very large mass to heat and it will take some time to get the oven into its optimum operating range.

cheezer 08-07-2013 09:19 AM

Re: remove the plywood support?
 
got it , thanks

caspian 08-07-2013 11:34 AM

Re: remove the plywood support?
 
Now i'm confused. I am in the process of making my oven and i have it in this order (from the bottom). 4 1/2" concrete, 4" vermiculite/portland, 4" brick.

Wouldn't it make more sense to have the vermiculite closer to the heat or do i have it backwards?

thanks
chris


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