Rocket mass heater Question

Ok
so I am new here and new too the whole Mass heater idea... Now i have watched the videos by Permies.com. I have noticed that most mass heaters are made from Cob. Now can one be made and use mortar or portland?
I do not have any clay in my area i barely have any dirt at all ..lol I need to know what other possibilities there are available too me.
Thanks Daren

Unfortunately, portland cement can't handle the temperatures.

See www.dragonheaters.com for some options which don't involve cob.

Well, refractory castable for the burning part, and

http://donkey32.proboards.com/thread/1049/small-diameter-backup-supply-works

The kaowool with the rigidizer might hold up, only time will tell. The cinder blocks however may not really the best option. Based on the size of the barrel he is using and the channel the question, the issue is, what is the temperature entering the cinder block area? It should be less than 400F, Since his barrel is small, it is likely his heat is higher than the 400F. Long term this will result in the cinder blocks failing. The other issue is that cinder block is not very good at thermal mass. See the chart posted at this blog. If you are going to make the compromise on temperature it would be better to use solid cement blocks.

But more firebricks would serve the best.

http://blog.dragonheaters.com/category/reference/thermal-mass/

Ok so portland bad... Motar ?
Also I didnt see any other possibilities with those links.. maybe I missed something

What sort of mortar? Does the mortar have lime in it?

Cindy Mathieu wrote:What sort of mortar? Does the mortar have lime in it?

I believe Mortar does have lime in it just like concrete does.
Are there any other options ?

Lime is the substance which doesn't hold up to the heat. It's the reason the cinder blocks will fail.

The chart on the Dragon Heaters blog shows the (short) lists of both heat absorbing and insulating materials which can tolerate the heat and are within reason cost-wise. Cob which is mostly clay is on that list, but it is not as good at conducting and storing heat as dense fire clay bricks. The reason it is the preferred material for rocket mass heaters on Permies is that, for most people, it is readily available and cheap (sometimes, free).

I originally sent you to the Dragon Heaters website because our builds use clay chimney flue liners as the structure to which you may adhere fire clay bricks for heat storage. In this way, you don't have to use cob. Our designs work really well, but building them is not free.

Sandy Mathieu wrote:The kaowool with the rigidizer might hold up, only time will tell. The cinder blocks however may not really the best option. Based on the size of the barrel he is using and the channel the question, the issue is, what is the temperature entering the cinder block area? It should be less than 400F, Since his barrel is small, it is likely his heat is higher than the 400F. Long term this will result in the cinder blocks failing. The other issue is that cinder block is not very good at thermal mass. See the chart posted at this blog. If you are going to make the compromise on temperature it would be better to use solid cement blocks.

But more firebricks would serve the best.

http://blog.dragonheaters.com/category/reference/thermal-mass/

Well, kind of he same numbers here, but not exactly, concrete does a better job at transmitting heat than firebrick. But doesn't accumulate as well, even with heavy loads of stones in it. One advantage, it's cheap.

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html

Concrete can cope easily with 100C°

http://en.wikipedia.org/wiki/Concrete_degradation#Thermal_damage And can whistand up to 300C° without too much damage. Worth a try for it's cheapness (tho, it's cheaper in europe, due to more widespread use)

If in europe, you can find pozzolan chimney flue elements (concrete with pozzolan) which are rated for 400C°. In the case i've showed, i don't know about longevity, but it's thermal conductivity is not as low as on your chart, because the conductivity is not dampened by the air gaps. His flue gases going directly through the place where the air gap usualy is. Well, worth a try on my side of the pond. May be not on yours.