Ive been reading about rock dust for the last couple hours. TLDR; im a stone mason. Is there any reason I couldnt use rock dust from crushing and grinding my own selected varieties of stone? This could be done with any one of the many diamond saws that get used daily. Secondly, the dust from this process (when wet) turns to almost a thinset composition... we call it slurry. It gets hard as cement. Would this not clog the medium in any fashion? Just ideas. Not sure if they are dumb or not. *edit- I would have loved to add to Jerrys thread 'rock dust' but this is more about grinding your own dust and difference between aged bagged product and fresh dust.
Marve, Welcome to GC, I'm a tile setter and a granite fabricator, I know full well how much dust we create in our stone related trades. I wouldn't worry about the rock dust you create yourself.....there won't be enough in your base soil mix to cause it to get rock hard. The other consideration is the use of Canadian Sphagnum Peat as a substrate material in your soil. Along with an aeration amendment, it will help to keep the soil from becoming severely compacted. I would use about 25-33% of an aeration amendment such as pumice, perlite, rice hulls or even lava rock. We used to discard a wheelbarrow full a week from the traps under our bridge saw in the fab shop. It was wet and like a sludge, but would dry out in a week or so. Jerry's Rock Dust thread will line you out on the amounts needed. Cheers, Chunk
Thanks Chunk. So by chance have you used any of the dried slurry from the granite shop? I already have Azomite in my mix, but would love to use a homemade dust in the future. Curious if you were confident enough in the dust the shop is creating vs something like azomite....
Righto. So just curious... At which sieve size does the presence of rock become negated? I thought I saw in another thread "screenings" be mentioned, which are usually 1/4" minus.
Hey Marve. I'm not in the stone trade, so I don't know the specific sieve sizes. But you want the rock dust to be as fine as possible, like a powder. You don't want rock "chunks", definitely as fine as possible. edit: quote "At which sieve size does the presence of rock become negated?" The purpose of the rock is to act as a sort of "home" or "anchor" for the fungi and microbes in your soil, and they like it as fine as possible. The goal isn't to have what we would consider small pieces of rock, but rather what microbes and fungi would consider pieces of rock (in other words, tiny tiny tiny). There is no sieve size at which the presence of rock becomes negated (unless that means something other than what I think it means). hth
I love how you described that there. Thank you. Sounds like 400 sieve minus is what they call home. Literally dust.
Agh crap. Forgot to mention this. If anyone goes to a quarry to try to obtain rock dust... DO NOT ask for "screenings". You will be getting 1/4" minus. Less than half of this will pass the 200 sieve and it differs from quarry on the composition. You want to ask for the "slurry" or better yet dust from any process that was not wet-cut. This should be given to you FREE as it's a waste product that most shops pay to have removed.
The smaller the particle the greater the total surface area which means more contact (anchor) points for the good guys.
The screenings I was mentioning was for limestone. Got it by the dump truck load to spread on the yard and where we got it (concrete plant), most of it was well under 1/4". More like coarse sand. Even still it would take years to break down. This was cool for yards, especially with the sugar sand that we have in SoFl. I didn't know squat about lime back then and mainly added it to my mix for a bit of weight. Guess there was enough dust in there to get things right in a month or so. Then again, I would add a couple of shovels of it to a wheelbarrow full. You are totally right with the 'dust' and sieve size vs screenings. Since I moved I tried 'chicken grit' size oyster shell and the same with granite. Both were totally worthless AFA affecting the soil in any way. Smaller than 1/4", but still way to big to break down in less than a year or more. Wet
Off the top of my head (as long as you are comfortable with it) you could put a 4" diamond blade on an angle grinder. Get some granite or local rock and grind away with a shop vac collecting the dust as you go. It will take a while... But will give you the right size material. Wear a mask though
Even easier is going to the landscape supply and getting a 5 gallon bucket of granite dust for $3. You supply the bucket and shovel. Really is a dust, they also have screenings and gravel size. The 'chicken grit' was from the feed store and before I found out the landscape supply would sell to the public. The hard part was catching up with the owner for the cost of the 5gal bucket. The salespeople only had prices for cy of the stuff ($28). Wet
Ur lucky man. I've never seen TRUE dust on the menu at any stone yards- and I've been to many. Screenings are a common commodity and as you said, I would dissuade against them... There is a % that passes the 200 sieve but not enough. I'm using Azomite for my first grow here, but I think I will make my own dust in the future.
THAT^^^^^^ is exactly what I did. LOL ~$45 for 20lbs of Azomite. Found the granite dust ~10lbs into the azomite. I'll still use it, I think it's great stuff, but I won't be ordering anymore. Not when ~75lbs of the granite dust is only $3. $2+/lb vs $0.04/lb. It would take a democrat to argue with that math. Wet
AND it's a better product - no heavy metals like volcanic colloidal clays like Azomite have. Win-win. J
If what is being said here is -"granite has no heavy metals"- then i would urge you to read this Is Granite toxic
^I *think* what jerry is saying is that granite does not have the same concentration of heavy metals as azomite. I too thought this to be true, is this not correct Sam? A while ago I was thinking about purchasing some azomite and did a little googling first and came across a couple links on how azomite is radioactive. That did it for me. Now, the information I saw could absolutely have been wrong and I just overreacted. I'll try to find the link and post it.
ITG, I have not read that about azomite. Not saying that it is not out there, I just haven't read it. Nor, am I saying that granite dust should not be used. I do think it should be used with a certain degree of safety, as in lung protection. And it does contain heavy metals and a degree of radiation. Most things mineral contain a degree of risk, particularly when used in the form of dust. Please, exercise caution. This is my message.
You are absolutely right Sam. Most any type of mineral contains some degree of heavy metals and can accumulate radioactive metals. Thanks for bringing that up, it's an important point that hasn't been talked about.