Post by cannyfradock on Jun 9, 2015 19:17:27 GMT
About 3 years ago I built a Pompeii oven for my boss (the oven is my Avatar pic)...last year there appeared cracking on the final render around the area which touched the s/s chimney. If the double sleeve insulated stainless steel flue is bought from new it will have a base which stops the outer skin of the flue from getting hot. My flue was picked up from a scrapyard for £8 (another budget build)...it had no base. The cracking allowed water to enter and started destroying the thermal blanket. As my boss is a carpenter a roof was always on the cards.....but never happened.
He removed the render coat, vermecrete and thermal blanket then had a "cunning plan"....he would use high temp. expanding foam directly on the brick dome and do away with both thermal blanket and vermecrete. He used 10 canisters of the stuff @ £6 a canister to create a 5" deep layer of waterproof, 1200c insulation layer. He destroyed the outer arch in the process so this is where I come in!!
n.b....the oven was still performing v.well even with the cracked render....and has since fired the oven with the expanding foam on it. The oven reached white hot in about 50 mins from cold on both occasions.
I hope to document the process of creating the vent while repairing the outer arch....here's where I start..
The oven still has it's inner arch. The picture shows the expanding foam.
I used off-cuts of 4" kingspan insulation to create my arch formers. I made the external arch one and a half bricks long. This will allow me to create a decent sized hole/vent for the chimney. The white pieces over the arch are 10mm slivers of thermolite block which will act as a heat stop between inner and outer arch.
This is the first half brick arch. The centre 2 bricks have been cut down from 4 1/2" to about 3" to create an opening of about 6" x 8".
This is the second part of the outer arch. A full brick is butted up against the half brick to create an outer arch of one and a half bricks long. The 2 center bricks are only half bricks. The picture showed the center bricks laid dry to show the effect of reducing the size of the middle bricks to create the vent.
My cheapskate boss won't buy a decent flue so I created a little more height (9") by using some old clay pavers on top of the arch to create extra draw.
He is again threatening to enclose the dome with a sexy roof structure. That way he could just use loose vermiculite as in-fill. I don't expect he will so I'll have to find a way of putting a waterproof render on top of those expanding foam worms that now lie on top of the dome......repair is on-going!!
To the rear of the clay paver stack I enclosed the stack with a thermolite block. This way ....if the dome is rendered the bit touching the stack won't crack from the heat.
Terry
He removed the render coat, vermecrete and thermal blanket then had a "cunning plan"....he would use high temp. expanding foam directly on the brick dome and do away with both thermal blanket and vermecrete. He used 10 canisters of the stuff @ £6 a canister to create a 5" deep layer of waterproof, 1200c insulation layer. He destroyed the outer arch in the process so this is where I come in!!
n.b....the oven was still performing v.well even with the cracked render....and has since fired the oven with the expanding foam on it. The oven reached white hot in about 50 mins from cold on both occasions.
I hope to document the process of creating the vent while repairing the outer arch....here's where I start..
The oven still has it's inner arch. The picture shows the expanding foam.
I used off-cuts of 4" kingspan insulation to create my arch formers. I made the external arch one and a half bricks long. This will allow me to create a decent sized hole/vent for the chimney. The white pieces over the arch are 10mm slivers of thermolite block which will act as a heat stop between inner and outer arch.
This is the first half brick arch. The centre 2 bricks have been cut down from 4 1/2" to about 3" to create an opening of about 6" x 8".
This is the second part of the outer arch. A full brick is butted up against the half brick to create an outer arch of one and a half bricks long. The 2 center bricks are only half bricks. The picture showed the center bricks laid dry to show the effect of reducing the size of the middle bricks to create the vent.
My cheapskate boss won't buy a decent flue so I created a little more height (9") by using some old clay pavers on top of the arch to create extra draw.
He is again threatening to enclose the dome with a sexy roof structure. That way he could just use loose vermiculite as in-fill. I don't expect he will so I'll have to find a way of putting a waterproof render on top of those expanding foam worms that now lie on top of the dome......repair is on-going!!
To the rear of the clay paver stack I enclosed the stack with a thermolite block. This way ....if the dome is rendered the bit touching the stack won't crack from the heat.
Terry
