Thermalite Blocks

[seanp]

I'm building a vault oven for both pizza and bread out of red clays with a lime (putty) mortar and on a wood base.  It's a budget build and I know it wont stand for 100 years but hope to get at least 5.  It's my first build and probably not my last so I'm not to fussed about longevity at this time. 

So I'm committed to using Thermalite blocks for the base with my reds laid flat on top for the hearth. Arch will go up on a form of about 680mm wide with 4 arches deep (~860mm deep) with an interior height of ~500mm.  

My question now is since the outside will be insulated and rendered is there anything stopping me from using thermalites for the exterior insulation?  I was thinking of bringing a wall up on the outside with 100mm block ~50mm from all arch walls and filling with loose vermiculite.  I would bring it up to just under the apex of the arch and put a render coat on top of the loose vermiculite (held with wire mesh) for a top insulation layer of say 4". All topped off with a cedar shingle apex roof on cedar posts.  

Is 50mm with 100mm block enough? 

My local Selco also carries thermalite coursing bricks that would allow more flexibility but at a higher cost per area.  

Any input greatly appreciated.  And if I'm being a numpty please say so, I have thick skin (and sometimes skull)

 

[chas]

Jul 12, 2015 20:02:41 GMT seanp said:

I'm building a vault oven for both pizza and bread out of red clays with a lime (putty) mortar and on a wood base.  It's a budget build and I know it wont stand for 100 years but hope to get at least 5.  It's my first build and probably not my last so I'm not to fussed about longevity at this time. 

So I'm committed to using Thermalite blocks for the base with my reds laid flat on top for the hearth. Arch will go up on a form of about 680mm wide with 4 arches deep (~860mm deep) with an interior height of ~500mm.  

My question now is since the outside will be insulated and rendered is there anything stopping me from using thermalites for the exterior insulation?  I was thinking of bringing a wall up on the outside with 100mm block ~50mm from all arch walls and filling with loose vermiculite.  I would bring it up to just under the apex of the arch and put a render coat on top of the loose vermiculite (held with wire mesh) for a top insulation layer of say 4". All topped off with a cedar shingle apex roof on cedar posts.  

Is 50mm with 100mm block enough? 

My local Selco also carries thermalite coursing bricks that would allow more flexibility but at a higher cost per area.  

Any input greatly appreciated.  And if I'm being a numpty please say so, I have thick skin (and sometimes skull)

 

Hi Sean, when you say 'bring it up to just under the apex', do you mean ' 4"above the apex'? Otherwise I can't see how you contain the 'top insulation of say 4" '. What you're suggesting is a blockwork box around the oven and 2" away from it, filled with vermiculite, with a 4" topping of vermiculite protected by render?
If so, fine - my only reservation would have been insulation over the oven - a naked skin of brickwork won't keep the heat in. Maybe try to get some angle(s) on the topping so horizontal rain driving under your shingle roof can't settle?

Chas

[seanp]

A picture is worth a thousand words...

I plan on laying the vermiculite in, wiring over then putting a thin render on so I have top insulation and also the waterproof coat for like you said, horizontal rain.  


Was also flirting with the idea of just doing a double dome, inner red brick and outer thermalite coursing bricks.  But not sure what muck to use so it wont act as a thermal pathway to the outside.  

Decisions....

[chas]

A goodly amount of rabbit for the dog to see now - It may be tricky/frustrating to render over the loose vermiculite, though small mesh wire or better, expamet would take a coat to firm things up before the final coating...

A bit of research here might yield the info you need about a brick/block dome's insulative qualities. Maybe you could use thin wire brick ties to keep the block barrel off the brickwork by a couple of inches and pour loose vermiculite in as you go. Don't use too many ties - I'm convinced anything that can expand when heated is best kept away from ovens. Loose vermiculite fill is better than vermicrete, but you could plaster 2" of vermicrete all over the bricks and then make your thermalite barrel 'cover', and then render that... more shapely and I'd guess brick/vermicrete/thermalite/render is as good as you need.

As you say, decisions...

Chas