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nissanneill 05-21-2007 06:09 PM

Bedding brick hearth to vermiculite insulation
Well we are under way.
The foundations dug, the plastic and mesh installed and the footings poured over the weekend for my Pompeii oven which will be between 1000 qnd 1100mm internal diameter. I mixed and screeded 100mm layer of vermiculite (very strange material to work with) onto the very fresh concrete foundation. Sorted the bricks and commence cutting and constructing the dome hopefully next weekend. I plan to have the first course of soldier bricks in and then cut the hearth bricks to fit. I installed 2 X 1/4"copper pipes for the thermocouples into the floor and plan another 2 for the dome. This should be enough to get going and once I have used the oven for a while, will simply draw on our experiences for bake numbers. I will get the 'near surface' and 'brick thickness' temperatures of both the hearth and the dome so should get a fairly good idea of 'soak' rate of the bricks.
I get the steel to fabricate the door frame and oven entry arch tomorrow and start the cast iron door patterns shortly.

The questions that comes to mind is:

1. since the vermiculite layer was mixed at between 5 and 6 to 1 (exfoliated vermiculite to portland cement) using a broad bladed fork (so as not to damage or break up the brittle material) and using just enough water to get the mixture to hold together (but could squeeze water out in a clenched fist), the finished surface although perfectly level and flat, is relatively porous and a little spongy (when compared to concrete). Is it wise to screed over this vermiculite layer with a very thin fine sand layer (like a beach sand at around 1-2mm thick) to bed the fire bricks into?
As I am using second hand bricks, some from different manufacter's and vary slightly in dimensions, it would be easier to achieve a flatter cooking surface,


2. I have sorted out the best from 200 odd bricks for the hearth, but since the firebricks are relatively brittle, (especially ones that have been used and handled several times before), would I be better off with a thin mix of refactory mortar to patch the few chips/grooves that will be present?
I would prefer not to mortar the bricks in place as they will be much more difficult to replace if needed.


PS. I am keeping a photographic record of the construction and will post the pictures when the oven is nearer completion, or would you prefer them as we go?

Bacterium 05-21-2007 06:37 PM

Re: Bedding brick hearth to vermiculite insulation
Hi Neil.....keen to see "in progress" photos :)

Balty Knowles 05-21-2007 07:11 PM

Re: Bedding brick hearth to vermiculite insulation
It would be good to see the work as it progresses.:)

arevalo53anos 05-22-2007 03:40 AM

Re: Bedding brick hearth to vermiculite insulation

Answering 1: Use a mixture of clay (soil or refractory clay - this last one you could buy at Home Depot) and sand 50-50.
This do perfectly your work


nissanneill 05-22-2007 05:10 PM

Re: Bedding brick hearth to vermiculite insulation
Thanks for your response guys,
I have posted the construction progress descriptor and pics in the Pompeii oven construction forum
Luis,will do as you suggested. It will only be a very thin layer but I feel that it is best to bed the hearth bricks in an an 'adjustable' base, especially to obtain a nice flat surface when using secondhand bricks that vary slightly in thickness.
Thanks once again.


Balty Knowles 05-22-2007 06:41 PM

Re: Bedding brick hearth to vermiculite insulation
I had similar results with my vermiculite, I smoothed the surface with a veneer of high temp cement prior to laying a sand fireclay mix as a bed for the floor & first course. I posted a pic in the photo gallery

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