Hi everybody.

Well, it's been somewhat discussed, but there's no definite answer. On Paul Wheaton's portable rocket video, he states his discution with Ernie, saying that pea gravel would be good. I assume pea gravel is pea sized gravel, like you find in tarmac? Any other size useable? I can get cheap and easy access to concrete mix. A mixture of gravel and sand. Would that do the job? Or should i stick to 7/14 8/12 or may be bigger, like 20/30? All thoses sizes are in mm.

Thanks a lot.

Max.

From what I understand, Satamax, you want to achieve the best density of material. That means maximizing individual surface while simultaneously reducing dead space between each stone. So: what type of gravel packs the tightest? The byword I've encountered is: monolithic.
The other factor, I guess, is what type of rock is the gravel composed of? High silica stone can have some insulating tendencies even though it's monolithic. A high feldspar rock like granite would fare better as thermal mass.

How about incorporating gravel into a cob mixture to make it monolithic?

Hi Chris.

Thanks a lot for your reply.

Well, two things. I have no clay where i live. Most of the soil is based on slate dust and organic earth. A fair bit of quartzite too, and some chalk byproducts, like tuff. I live on a cleavage between old volcanic and ocean's depth type of stones. No clay anywhere close. And besides, i don't want to go monolithic, as i want to move to my own place within a year or two. And want to take my stove with me. Then, i'll do a cast mass.

Here's where i stand!

Thanks again.

Max.

foregoing the monolithic part will not work. I filled mine first with crushed gravel, which means pea sized down to 'fines' so that when tamped all the different sizes lock together. I left the top of the mass open and would check to see if the gravel directly over my flue was getting warm. it did not. Then I went with the experienced advice - monolithic. Pulled out my gravel. Mixed it with dissolved cat litter, re-apply. Now it works very well.
monolithic and easy to disassemble. Messy but easy.

- what rich is describing - is usually called crusher-run in the business, packing it tight for best contact with the piping can put you in danger of collapsing your stove pipe.It will also be hard to remove when you want to remove it later !
It may be possible to use one of those vibrating tools used to make sure there are no voids in poured concrete to ensure compaction around your stove pipe. I personally have never used that tool for that purpose. Clay is universal,though it can be extremely local at the same time, try the art department at your local C.C. they end up cleaning up different grades of clay into a slop bucket and that mess is not good for firing but would be good for a clay sand mortar mix and as slip for mixing with builders sand to fill in the air spaces between the grains, again because you want to re-move this stuff a little goes a long way . Its a little late in the year for a scouting trip floating down a river in a canoe looking for clay. Try hanging out at a farmers supply store that actually sells bulk animal feed, the driver of the bulk delivery truck will know where there is clay! He probably covers 2-3 counties in a weeks run ! The store owner, if the owner knows his customers, he knows whose truck comes in covered with clay ! Mostly thats just me putting my two cents in, for what its worth! - g'LUCK, - Pyromaticly yours, - Allen L.