Castles made of.... Sand?

[rhyddid]

Thought a post on the thermal mass of sand might be interesting.

I do know that sand can be desperately hot by day and cold as hell at night at the beach! ... but im curious to hear what findings people have had with different grades of dry sand as insulant.

[Donkey]

Errr......
Good question.. I know it works and is my preferred thermal mass in benches. It is just so easy to work with, pour it in and it pretty well does the rest.. As to how differing grades of sand perform thermally, I have no idea whatsoever..

I can say that I tend to gravitate twards stuff that has a big variation of grits with the larger sizes almost too big to call sand... Which is pretty much the best stuff for cobbing with anyway so Ive usually already got it on the job.

Anyone else?

[canyon]

Sand is a pretty variable variable. I have experience with several sources in my area for different construction methods etc. but not as insulant. I would think density is a good indicator of the relative insulant value of dry sand or matter in general(the lighter per volume the more insulant). I'm with Donkey that sand is more advantageous as a thermal mass storage than insulant (on its own) due to its higher density than say ash (which I would like to experiment with for refractory insulation).

[droesinger]

My partner and I are hoping to buy a small property where we can start getting our hands dirty with some of these ideas.

I have a small timber-frame shed that I use as my blacksmith shop at present, but when we move, it will become my partner's framing studio. We want to heat it with a rocket stove feeding an earthen mass floor.

I'm thinking a 6" system will be ample, as the shed is less than 144 sq ft.

We were thinking of adapting the floor system described in Hand-Sculpted Houses by using sand for the layer of floor where the pipes will be laid. We thought a layer of vermiculite or perlite after the stone drainage layer, then the pipes laid in a layer of tamped sand, to be followed by a cob layer or two and a poured adobe skin for the final surface.

Does this make sense, or do we need to worry about sand filtering down to corrupt the drainage layer? Pouring and tamping sand just seems easier and quicker than cob for that layer.

Dan

[Donkey]

Sand will infiltrate the drainage layer if it's placed directly on top of it. Vermiculite and pearlite will do the same.
You don't need a very thick layer of cob to seperate these things. Something like a straw/clay plaster could be used under and thin (2-3 inch) cob walls between areas.

6 inch is probably fine, though 8 inch systems can be nicely energetic. Seems better to have the juice when you need it.

[droesinger]

Thank you, very helpful info there.

Sounds like it'll be a pretty deep floor, but that's fine.

Anyone here know of a practical and relaible way of creating the ductwork without using metal pipes, whether for floors or benches or otherwise? I'm thinking expense and the possibility of eventual corrosion here.

Dan

[Donkey]

Really, the pipes don't have to be brand new. They should be in fairly decent condition but you could get them from your local dump/scrap yard. Depending on where you are of course and what kind of policy they set.. Our local dump/landfill closed and re-opened as a transfer station. Everything gets shipped off to Nevada or some such place which costs loads of money. The official policy is no salvaging, though the reality is take as much as you can, then they don't have to pay to have it hauled.

As to corrosion, it seems immaterial. It will simply leave a void in the cob. As long as a chunk of corroded pipe doesn't fall and block things up.. Perhaps you could use something else as a form? like cardboard tubing or something..
The only thing to be aware of is that cob is a pourous material and could leak dangerous gasses. I kinda doubt it, though the danger exists and one should be wary. Best practice is to use some kind of air tight liner, like stovepipe. Even old stovepipe with heat tape over any holes is better than none.
Really, since this question comes up so often, someone needs to test this one out. Perhaps it may be nothing, though the tests HAVE NOT been done yet. Until then best not to bet your life or the life of your family on it.

[droesinger]

Are there any non-porous coatings that could be applied to cob for the ducts?

It would be nice to find a way to reduce the materials needed, especially manufactured items like steel pipe.

What sorts of toxic gases are we looking out for here, just carbon monoxide? Are there testing devices like CO detectors one could use for such a test?

Dan

[Donkey]

I like your thinking here.
As to non-pourous coatings.. Good question.
It occures that whats called water glass or sodium silicate has been used to waterproof cob. I know of cob sinks and have heard of a cob bathtub..
As to it's fire resistance, well its used to patch leaky mufflers and whatnot.. I haven't used the stuff myself and I have no idea as to how it's made or what kinds of toxic crap is produced as a byproduct..

CO.. as you say is the biggie. Yep CO detectors would be a good start.
I would sure like to know if it's even a problem. It's my FEELING that there is no problem, that the CO and whatnot would take the path of least resistance, out the flue.
The sticky bit is that it would need to be built, cob bench and all, and used for a time, to know either way. It's a good deal of work for a possible throw-away or do-over. Not something that I can recommend, though I CAN sit here quietly and wish someone would just do it and let us all know.

[chronictom]

I wouldn't swear to this by any means, but why not just mix a little sand and a lot of clay (30/70) and add a thin layer to the pipe, fire the stove, let if get hot (fired), wait til it cools (and cracks), re-coat it again, packing the cracks, fire it again, etc etc. a couple of times?

Would you not end up with a solid clay pipe that didn't leak?

Tom

[Donkey]

Nope..
Unfortunately, the first firing bisques the clay, turning it into pottery, no longer clay. The filler layer can't become one with the rest. Once the clay body cracks, it's a done deal.

Apparently, often the sand can be the cracking problem.
Sand is mainly silica or quartz. A crystalline structure.. When heat is applied to them, they tend to deform, change shape and/or expand. It is this expansion/contraction that can play havoc with homemade refractories/brickworks.
Grog is a better aggregate for high heat purposes than sand. Crushed, fired clay(s) are grog. Powdered pottery, brick (old red brick is great) etc. can be used. One COULD toss a few dried clay balls into a fire, bisque 'em, crush 'em and call 'em grog.
Use it in place of sand in the mix. It won't deform like sand under heat and is far less likely to crack.

[johnjmw]

I just reread this topic. Donkey, How are you using the sand to fill the bench? Is the pipe in the bench cobbed at all or is there a trough built, pipe placed in a bed of sand then sand filling the trough, then cobbed over? I like the ease of this idea. A lot less work to cob. But if / when the pipes start to rust or burn out the cob could be self supporting, the sand would collapse immediately. I think. How well does the pipe hold up inside the bench? I know in the book Ianto says the barrel he is using is the original one he installed something like 20 years ago I think.
My original idea was to use sand with just enough clay to hold it together, something like 10:1 or 20:1 sand:clay. Then use cob on the outside to create the bench and give it a little more strength and resistance to wear and tear.
John

[Donkey]

I'm not really sure about how long the pipe will last in there.. Yes, a thin layer of cob around it would last long after the pipe itself fails. I expect that the pipe would never burn out in the bench, just not hot enough in there, except perhaps right against the outflow from the barrel.. Though, there shouldn't be any oxygen there.. No oxy, no burn.

I just cob a trough, place pipe in trough, fill with sand, cob over.. It is easy and provides better connection with the thermal mass.

I think that what you said makes a certain amount of sense. Just a touch of clay content to keep the sand from flowing free. Keep it from working it's way through small holes or cracks, etc.
Still, this would be just a filler. I would rely on the cob for strength, NOT the sand/clay mix.

[Teach]

Consider a different approach.

Wrap the pipes with a sacrificial layer of something like building paper or cardboard. Then coat the cardboard enclosed pipes with a home made refractory mix something like the recipe posted over at our freinds www.backyardmetalcasting.com website. Fill in and around the encapsulated pipes with sand to fill the trough and then cap with cob and finally plaster.

My thinking here is the paper layer will burn away to fine charcoal but in doing so then creates a small space between pipe and refractory so the pipe is free to expand and contract without causing the refractory to crack. Once the pipe deteriorates you still have a sound (hopefully) refractory channel to carry the gasses.

Yes, no?

[Donkey]

.. Refractories tend to be insulative.. Otherwise this could work just fine.
I don't know if the extra expense is really worth it though.
The same "paper gasket" thing could be done using heat-core cob..
'course, I think that about halfway down the bench, it won't be hot enough to burn out the paper anymore and it might just sit there and insulate the pipe away from the bench.

Really.. Seems to me that simpler is better. Not to be lazy, but the less you gotta do, the better off you'll be. Less that can go wrong, less to figure out later, less to figure out before... ETC.