BULK DENSITY IS NOT A MEASURE OF MUSCULARITY!
Bulk density is, however, a term worth understanding if you ever purchase bulk materials from a landscaping yard.
Here you are at your local landscape supply store and suddenly you find yourself confronted with the concept of bulk density.
So what is bulk density and why is an understanding of this important?
Bulk density (BD) is defined as the weight of a material in a given volume.
The 'given volume' the material weight is measured against (in the case of the landscape yard) is 1 cubic metre (1m3).
Different materials have very different weights and therefore different BD's.
1m3 of River Rock, for example, will have a weight of around 1.5 tonnes, so the BD is 1.5
1m3 of Road Base will weigh around 1.7 tonnes, so the BD is 1.7*
*In these two examples the road base weighs more than the river rock because there are more air gaps or 'voids' in the 1m3 of river rock.
1m3 of Garden Soil will typically weigh 1-1.2 tonnes, so the BD is 1-1.2
Bulk density has some bearing on the delivery, because the delivery trucks are rated to carry different maximum loads yet more often than not the yard is selling you a product based on $/m3.
So, for instance, a smaller tip truck might be rated to carry a maximum 6 tonne load.
Lets say you want 5m3 of river rock.
With a BD of 1.5 that's going to give you a weight of 7.5 tonnes, so it's either a second delivery or a larger truck such as a body truck with a load carrying capacity of around 12 tonnes.
But bulk landscaping materials are not universally sold on the basis of $/m3.
Some landscape yards sell some products based on $/tonne.
Although I'm certain this is not deliberately done to confuse the customer, it could be argued this sometimes does have the effect of...... confusing the customer!
If a landscape yard is selling a bulk material based on $/tonne and you want to compare the price with another yard selling $/m3:
Multiply the cost per tonne by the BD to get the cost per m3.
Using 20mm River Rock at a hypothetical sell price of $100/tonne -
$100 (sell price/tonne) x 1.5 (BD) = $150.00 (sell price/m3)
Conversely, if you want to convert $/m3 to $/tonne:
$/m3 multiplied by (1 divided by BD) = $/tonne
Using the same 20mm River Rock example -
$150 (sell price/m3) x (1 divided by 1.5) = 150 x 0.666 (recurring) = $100/tonne
$/m3 or $/tonne? Does it matter?
Is there a preference as to which method of selling is better for the customer, per tonne or per cubic metre?
Yes and no.
It could be argued the loader operator who is loading the truck has more bearing on the outcome than whether the product is sold per tonne or per m3.
Like most occupations, there are those that care about what they are doing and those that don't.
Good landscape yards will have competent and experienced guys (gender plurality being used here) loading.
Loaders will have buckets certified to a certain size ie; 0.33m3, 0.5m3.
And the amount of product loaded will be reasonably accurate.
If the yard sells some products per tonne then the loader will have certified scales to read the weight of product.
If you are unfamiliar about a certain yard before purchasing from them, it can be useful to swing by and check them out to get a feel for how professional they are.
Pay particular attention to the loader in operation and the degree of care being exercised in the loading process.
So, what about per tonne versus per m3?
Assuming all other factors are equal, it shouldn't matter.
This is especially true with products like gravel and pebble.
Where it becomes a little trickier, especially where a product is being sold per tonne, is where that product has the potential to hold water ie; soils, mulches, sand.
Bulk materials aren't cheap so you definitely don't want to be buying a product with an excessively high moisture content because it rained solidly for the two days prior to you purchasing.
That's another reason why its a good idea, if at all possible, to check out the yard prior to purchase. Confirm the status of your product before it's loaded.
And remember this, if the yard is selling based on per tonne, and the product seems to have a bit of moisture in it, you can ask that they load based on m3 rather than weight.
In this situation reputable yards will do this anyway, so should not be at all offended by this request.