This is an online calculator for calculating the depth of compost to mix with the soil, but you can also use it for any amendment. See if this is close to what Redenta's told you and then go with the lower figure. That expanded shale is very expensive.

Here is a link that might be useful: Soil Amendment Calculator

Thanks for the link denisew...
I put in my info and it says I need 1.2cu yd of material. So, how does that translate into 40lb bags of shale?
That would also mean I need 1.2cu yd of compost...it comes in 2cu ft bags. How does that convert?

Here's a formula or 2 cu ft. bags of anything.

Square feet X inches (In decimal divisions of feet ie. 3" = 0.25 feet, 4" = 0.33 feet) divided by 27 to get cu. yards. Then multiply by 13.5 (the number of 2 cu ft. bags in a yard)

So, you would do, (49 X .25) / 27 = 0.4530737 yards
0.4530737 X 13.5 = 6.11 bags

If you are using 3 cu foot bags, just multiply by 9 instead of 13.5

I don't know how that translates into 40 pound bags, but I'd be concentrating on mixing in good cotton bur compost and use the shale as a secondary ammendment you can do easily without.

Hope this helps and doesn't confuse.

Sally

I agree with Sally.

So far as I am concerned, the shale is just something for them to sell. It isn't necessarily something we need to use.

I have clay soil as well, and have amended it with compost from the cotton gin and my compost piles. It is friable up to my elbows in beds that are not walked on, after 3 years. It gets better every year.

Good luck.

Janie

My calculation is probably too late for you. According to my calculation, you need 14 bags to fill 1.2 cu. yard and very close to Redenta's calculations of 12-15 bags.

I googled the density conversion factor for light-weight expanded shale, and itÂs 30-50 lb/ft3. I chose the 50 lb/ft3 density figure as the representative conversion factor.

At your 1.2 cu yd required depth of area x 27 ft3/cu.yd x 65 lb/ft3 x bag/40 lbs = 52.65 bags, or you need 53 bags to fill the area with 6" depth.

Assuming you mix in 1/4 shale with 3/4 soil and compost (or whatever shale amendment ratio you choose for your 1.2 cu.yd bed), then you would need 1/4 of 53 bags, which is 13.25 or at least 14 bags. If you want to amend the top 6" of your bed with 50:50 shale/compost-soil for more porosity, then you would need more bags of shale or 1/2 of 53 bags, which would be 27 bags.

Sorry I used the wet 65 lb/ft3 density unit instead of the stated dry 50 lbs/ft3, so it would be 41 bags instead of 53 bags at 100% coverage. You would need less or 11 bags of shale (instead of 14) if you want to use 1/4 shale with 3/4 compost-soil to cover the required area. You get the idea. Redenta's calculation of 12-15 bags is about right.