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I got mine at Armstrong Garden center in Temecula. It wasn't coarse, probably medium. $20 for a 3.5 cu ft bag. The only coarse I could find was at a Hydroponic store also in Temecula but it was $35 a 4 cu ft bag.
You'd think living in North San Diego county with all the nurseries you'd be able to find vemiculite easily and inexpensively, but noooooooo..........only great price was at the pallet level. Not going there.
Lowe's and HD just have the 8qt or 2 cu ft stuff at around $20, so I passed. Lowe's advertised $23 vermiculite online, but they don't have it and can't get it.
So, I found both vermiculite and perlite at Grangetto's Farm & Garden Supply in Escondido. Coarse Vermiculite: $28.50/3.5 cu ft bag. And....coarse perlite for $11.59/4 cu ft bag. So I bought 3 bags of perlite and one bag of vermiculite. I couldn't believe the price difference!!
Advice needed: Just double-checking, but can I still use the 6:1 perlite/portland cement mix in my hearth and be okay? I've seen some mix recommendations as high as 12:1. What I don't use of either I can take back or use in my seedlings.
Any other final tips (I don't want to screw it up)?
Can't comment on the ratios for perlite, but you're correct: you can go 12:1 or as high as 6:1 on the vermiculite. I went with 8:1. Just know that the higher the amount of Portland the lower the insulation value. You might want to hang on to any vermiculite that's left over in the event you insulate your dome with it.
Well, for better or worse the hearth got poured today, both the structural and the insulation. It took nine(9) hours to do both.
The structural portion went uneventful. All the forms held. It took 1,350 lbs. or dry concrete mix (15 bags @ 90# ea).
The insulation portion was not quite as easy. I ran out of material and had to make a run to HD. I used 12 cu ft of coarse perlite (3 bags X 4 cu ft ea.), 1 bag of 3.5 cu ft vermiculate, and the 2 cu ft bag of medium perlite from HD. I also used a little more than 1-1/2 sacks of Portland (90# ea.) cement - about 140 lbs. or so total.
I never dreamed I'd use 17.5 cu ft of insulation. My hearth is about 6X6.
So I have a frankenstein hearth. I just hope it works.
Quick question: it the insulation suppose to be compacted? Maybe that's why I used so much.
I used 6:1 pearlite and it worked well. The key to mixing it is to make a cement slurry separately and then pour that into the pearlite then mix with a hoe. To make the slurry I used a twirly type paint mixer in an electric drill.
I mixed the perlite and cement dry until it was well-coated and than added water. It worked well, but I just used a lot more than I thought. I'm still trying to figure why. Maybe my hearth was bigger than others.
It's already setting up well, so in a week it should be rock-hard.
How do I get the finished concrete look. Right now it looks like Route 66 outside of Kingman, AZ. Perhaps just take a sand and cemet slurry?