Tyrone Slothrop

Deb Stephens wrote:I just had a thought. We dismantled an old glass kiln once and it had huge slabs of a material that was sort of like massive firebricks in it but they weren't the usual color. We figured they must have had some sort of insulative application. Could those be a mixture of clay with something fire-resistant and yet lightweight and insulative--like vermiculite or glass beads, etc.? Have you tried just googling firebrick images to see if you can find something similar?

Yes.   Everything was variations of yellow-tan bricks.

I think what I've got is cinderblock... More fire tolerant than clay, but not as much as firebrick.      I'll used it where a second layer, not directly fire contacting, is required.

Deb Stephens wrote:Those look like firebricks to me, but I'm certainly not an expert. The ones we have are yellowish-tan and have a groove on one side and a corresponding ridge on the other side so that they can be fitted together in the same way you would fit tongue and groove boards. Do yours have a ridge on the other side? Also, firebricks tend to be pretty heavy compared to regular clay bricks.

My firebricks are yellow-tan as well.  These are cinderblock-grey.    Flat on other side.

I got these from an outdoor fireplace demolition.  

They look like same/similar material as cinderblocks.

How are the heat-shock handling properties of these bricks?

Can I used them as a base under firebricks, to save on firebricks?


Pictures attached.    

Daniel Ray wrote:6" is really shallow, what are your temperature lows? An insulation skirt around the footing will trap heat from the earth and prevent frost heave.

This is GREAT information, and answers my question perfectly.

It also helps me articulate why I won't insulate underneath the footing.

My only concern is that the footing will be at grade, meaning the foam will be accessible just at the surface, and will get beat up.

I'm sure I can solve it, but would be interesting to hear if anyone else already has.

Concrete footingwill be buried 6" deep, with the top at ground level.

I'm inclined to put rigid foam on the external facing side of my footing, thus allowing the footing to benefit from the internal heat of the greenhouse.

Someone else suggested using ICF, but I don't want rigid foam taking up space on the inside, or be where I may accidentally dig it up.

Someone else suggested foam UNDER the footing to prevent chill.

Any ideas?  What have others done, and why?

Thanks everyone for replies!  

To answer questions, I', in Zone 3.   Wall will be poleward, but beside a garage/windbreak.

I'm planning to bond the rigid foam insulation to the outside of the cinderblock using pl400.    I'm planning to then cover the insulation with something like structural skin from conproco.

I'm hearing a lot of recommendations to use Sand instead of concrete to pour into the rock filled cores.     Can anyone confirm if sand is superior to concrete as fill?    

I'll leave aside the aircrete idea.    

Trying to find the sweet spot between thermal mass and insulation.

Design already has a water barrel for thermal mass, and will have foam panels on the outside of the cinderblock.

But how to fill the cinderblock?

1)   Fill with rocks, and then pour cement over, for total thermal mass?
2)   Fill with rocks and gravel, for thermal mass, and some insulation (Air between gravel).
3)   Fill with rocks and then pour Aircrete over?

What's the best tradeoff?

Abe Connally wrote:and here's from Ianto's book, Rocket Mass Heaters, page 23:

OIC. Thanks for the clarification. I do see the value in this.

A quick google shows various manufactured options, although I acknowledge this may be contrary to the frugal/recycling spirit of the exercise.

http://www.woodlanddirect.com/Chimney/Access-Cleanout-Doors

Abe Connally wrote:for the one below the feed tube, it will be 16 gauge metal, welded up to form a box. I may put a grill above it to prevent whole sticks from falling down in there.

I am new to this, so please take my concerns with a big grain of salt, but it seems to be that grilled compartment below the combustion chamber would be a de-facto increase in the open space surrounding the burn chamber affect air flow and burning.

I think this is a great idea... but I'd be interested to hear if it's been actually done successfully before, and how.