Underfloor insulation

[bigandy]

Hi Folks,

I've finally finished building the base of my barrel/vault type brick oven, and I'm ready to start on the interesting bit now. I have a nice level concrete plinth to work on, and the first job is the floor of the oven. This will be firebricks laid flat (to give a 76mm thickness). I could do with some insulation underneath to keep the heat in.

I was planning on using some thermolite blocks under the firebricks, but I am now wondering whether a sheet of insulation material like ceramic fibre board, would be a good alternative? Or, would it be an idea to do both, for the ultimate in an insulated floor?!

Finally, I have seen images where Aluminium foil has been used over insulation layers. Is it recommended to fit a lay of this between the firebrick floor and the insulation at all? What purpose would this serve?

Cheers
Andy

[pete123]

Hi Andy,

I put foil on my Calsi board on the advise of Liam from kiln linings to stop it getting wet.

I also put a walkers Space blanket on mine but that was a bit of a waste of time because it didn't have any thermal properties (the shine was painted on) - other than it probably added a bit of toughness. if I'd nicked it with a trowel I think the foil might have ripped?

My guess is you won't get much extra benefit from using both blocks & board.

[turkey]

it depends how think the board is, if you can afford a super thick chunk or two layers then really the blocks will not be getting any heat to insulate. Both are tried and tested so its personal choice.

the board is specific for this type of job so is probably the ultimate material if that is what you are aiming for, you can always have a thin layer of vermicrete as well as no doubt you will also use this in over dome insulation, this is more common than thermalite blocks but will mean longer drying times until you can start with the bricks.

[bigandy]

Hmmm. I think I'll use just thermolite blocks underneath, for speed of building! I'm not restricted on height (yet!) so the 100mm of thermolite block will position the floor of the oven just nicely at chest height.

I'm not sure about the insulation on the top yet, I haven't decided whether I will be vermicreting over then render, or building a block type enclosure and loose filling vermiculite....

Andy

[bigandy]

These are the blocks my local builders merchant stock:

www.heidelbergcement.com/uk/en/hanson/products/blocks/aircrete_blocks/thermalite_shield.htm

They seem okay?

Andy

[turkey]

any aireated block should be fine, the best of the best would be thermalite turbo which have slightly better thermal properties but really doubt you would even be able to test the difference without some very very expensive equipment, let alone test the difference once the oven is on it.

I would make sure when they go on you make every effort to keep them dry as you do not want a wet sponge under the oven :-)

[tonyb]

Its generally accepted that the finished floor height should be about elbow height for ease of use.

[bookemdanno]

I used a mix of Kiln Insulation Bricks and 3" Celcon Shield over a 2" Council Slab base and i felt no heat just after a 3 hour burn! Storage heater blocks under Quarry tiles for a hearth. The storage heater blocks i used were the ones that have a recess, so there is a smaller surface area in contact with the Thermolites.

[bigandy]

The Thermolite shield blocks went down on Saturday. Unfortunately they were a bit on the damp side when delivered by the Builders merchant. I've got everything under a poly tarp to keep the rain off for now, so I guess I'll just have to get a fire going little and often to dry it out over time

I've taken delivery of teh firebricks from Kilnlinings.co.uk too, so the next job is to lay the hearth, and then get some barrelly vaulty goodness on top too!

Cheers
Andy

[turkey]

a wise man once said a picture speaks a thousand words.......

glad its going well, with the current weather I am sure they will dry out quick enough. I had to re wet mine to get the sand fireclay mix to a nice consistency or it just sucked that dry and there was no grab when laying the hearth, then had plenty of time to dry again as a dragged my heels on the build lol.