Better or best mass materials

[scottiniowa]

I know in general, we use what we got for mass material, but in this case, I can get a lot of different things.

One of them being what we call sugar sand, a very fine sand that has smooth edges rather than sharp so not suitable for concrete. Thus pretty cheap and mainly used for fill. (local sand pit wash outs)

I have a very large (internal ) cinder block wall behind the stove, but need to fill the mass area between this.

This is a basement situation, so will have to carry in/down everything. Stove works great, now have to (would like to better) store the heat, produced.

This sand could fill every void, but have not really seen it used, rather, rocks-gravel-cob mixtures have been shown often. I don't think there would be any insulating effects with the sand, but thought I would ask those in the know!

[pinhead]

I've not used that particular type of sand but I have used loose river sand (smoothed edges from being under flowing water) and it's more insulating than conductive. You can use it - but I would mix it at about 4:1 or higher ratio with clay. Since you have a form to hold everything together, you could probably get away with an even higher ratio.

[Orange]

sand has air gaps, that's why it doesn't work well.

[scottiniowa]

Orange and others, I figured that the rocks and gravel and so on, also had their share of gaps as well, but I see what you are saying… I will keep pondering a method to proceed. Thanks.

[matthewwalker]

Gravel is also a very poor mass material.

[scottiniowa]

Am going to answer my own question here, or at least show a connection that answer the basic holding ability for BTU’s
blog.dragonheaters.com/burning-wood-thermal-mass-material-selection/

Looks to be a clear winner on storage but as well a clear loser on safety Kinda goes back to the “on one hand you have this, on the other hand you have this other thing to contend with” saga!

[scottiniowa]

Update- I have used some of the same clay used in ceramic's mixed with my Sugar sand and it is working well. I was watching some of Paul W's videos on his stoves (more than one) and in one he appeared and said he used p-gravel for the mass, I also have this close at hand and pretty inexpensive, though not near as cheap as the sugar sand. Certainly would be less work to "pour the P-gravel" around the pipes... Is this a good working way for mass storage of heat? I know there are many good ways, but I always have to keep in mind, that everything "gets carried into the basement"

Thoughts?

[ronyon]

Since the material isnt structural at all, why not just use soil?
Dig it up, bring it down in buckets,pour it in the void, and tamp(stomp) it in place.

On the other hand, is the cinder block wall part of the foundation?
If it is, you might not want to tie it to your mass.
You might in fact wish to insulate your mass from the foundation wall and the huge heatsink that is the earth itself.

[matthewwalker]

Don't bother with the dry gravel. It's not worth your effort to carry it down there. Use solid masonry, or clay/sand/gravel packed tightly.

[scottiniowa]

thanks Matt, I will scratch out the thought...And like you say, I certainly need it to be worth the effort.