New member, first oven build

[UtahBeehiver]

Pictures would be nice to help answer any questions you have.

[david s]

There is so much free water in the vermicrete mix that it's not really necessary, but covering for a couple of days will prevent the surface from drying out. Getting rid of the water is more important. See the attached experiment I did on vermicrete drying that you should find useful. It takes way longer than you would think or appearance suggests. You could try plunging a cheap garden moisture meter into the middle of the layer to get a reading.

Vermicrete insulating slab copy.doc.zip

[Michaelh]

Fire bricks are cut and laid for the floor. Tomorrow I will be building the sand mould and casting the dome. I have no idea how long that will take so may or may not get around to doing the tunnel

[Michaelh]

OK so some major progress yesterday as I have cast the whole dome now.
Do I remove sand today or tomorrow? And how long after do I start fires?

[david s]

Because you’ve used a proprietary castable which uses CAC then it does not require damp curing. You should probably form a sand mould in front of the oven mouth and cast the flue gallery first, then you can remove the sand and insulate the dome. Then start the drying fires. Getting an uninsulated dome hot, risks cracking it.

[Michaelh]

The flue gallery is cast by using an mdf and sand mould, it is visible on the floor in the first picture. When I remove the sand I will use Vermicrete to fix the two pieces together so when should that be done?

[david s]

If you’ve already cast the flue gallery, remove the sand from the dome, fit the flue gallery and start the insulation. It would not hurt to leave it for a week to let wind and sun do some of the drying, then do the drying fires.

[Michaelh]

Thanks David. Are you suggesting to insulate (ceramic fibre blanket and Vermicrete) before doing curing fires?
I thought the ceramic sheet didn't react well with water (/steam)

[UtahBeehiver]

Installing the ceramic blanket prior to curing will minimize temperature differential between inside and outside of your cast dome reducing the potential for cracking. Water vapor will migrate through ceramic blanket. CaSi board (floor insulation) is more affected by water in liquid state. You can install the vcrete after the curing but it will need to dry out before you do you final rendering or coating material.

[Michaelh]

OK cool. So the plan should be:
Anytime from tomorrow: remove sand, fit flue gallery and insulate. Wait 1 week then do curing fires. Then render. Let dry and paint.
Sound right?

[david s]

Yep. That’s what I’d be doing.

[Michaelh]

OK so I've got some way along now. Ran out of vermiculite though! Some on order which will hopefully arrive tomorrow. Thanks for all the tips so far.

[Michaelh]

So I have finished the vermiculite layer. I have somehow used 4 X 100 litre bags and it does not seem quire enough. I've bought a bag of perlite as it's a little cheaper and I intend to use this in a scratch coat render with lime, sand, cement. Then a thin top coat of just normal render.
Firstly is there a problem with doing this?
Secondly what would the ratios be for the perlite render?

Thanks