Little John
Drone Bee
- Joined
- May 27, 2012
- Messages
- 1,655
- Reaction score
- 4
- Location
- Boston, UK
- Hive Type
- Other
- Number of Hives
- 50+
I'll openly admit that the reasons I'm looking at alternative materials is that a) I've just bought some more wood to make a KTBH, and my wallet now hurts, and b) some time ago I inherited several cubic metres of horticultural Perlite which hasn't been touched in well over ten years.
So this afternoon I decided to run some figures, and this is what has resulted:
I'm using Cedar (with 12% moisture) as a reference, which has a density of around 23 lbs/cu.ft.
The density of a cement/perlite mix is:
1:8 22 lbs/cu.ft
1:6 27 lbs/cu.ft
So, they're not outrageously different.
Turning next to Thermal Conductivity (k = W/(m.K))
Cedar has a TC of 0.21, whereas Perlite is a much better insulator at just 0.031 - even when we add-in some Portland Cement (at 0.29) - giving a TC for a 1:6 mix of 0.08, and a 1:8 mix as 0.07
But - back in the real world, I'm guessing that a thickness of at least 3x that of wood would be needed for equivalent strength.
I made-up some test blocks a couple of years ago to see if using Perlite with Cement was a viable proposition, and the end-product turned out to be good, and very light. But I never tested it to destruction - wish I had now. If I should find those test pieces, I'll take a hammer to 'em.
So, the bottom line is that a hive made from a Perlite-Cement mix will have walls 3x the thickness of Cedar, but having 7x it's insulation value.
However, the Perlite-Cement hive will be 3x the weight of a Cedar hive, or 2 to 2.5x the weight of one made from a heavier pine. Hmmm.
The next thing to consider is the logistics of how best to fabricate with this material, but before doing so, I thought I'd ask here first in case someone has ventured down this particular road already ...
So this afternoon I decided to run some figures, and this is what has resulted:
I'm using Cedar (with 12% moisture) as a reference, which has a density of around 23 lbs/cu.ft.
The density of a cement/perlite mix is:
1:8 22 lbs/cu.ft
1:6 27 lbs/cu.ft
So, they're not outrageously different.
Turning next to Thermal Conductivity (k = W/(m.K))
Cedar has a TC of 0.21, whereas Perlite is a much better insulator at just 0.031 - even when we add-in some Portland Cement (at 0.29) - giving a TC for a 1:6 mix of 0.08, and a 1:8 mix as 0.07
But - back in the real world, I'm guessing that a thickness of at least 3x that of wood would be needed for equivalent strength.
I made-up some test blocks a couple of years ago to see if using Perlite with Cement was a viable proposition, and the end-product turned out to be good, and very light. But I never tested it to destruction - wish I had now. If I should find those test pieces, I'll take a hammer to 'em.
So, the bottom line is that a hive made from a Perlite-Cement mix will have walls 3x the thickness of Cedar, but having 7x it's insulation value.
However, the Perlite-Cement hive will be 3x the weight of a Cedar hive, or 2 to 2.5x the weight of one made from a heavier pine. Hmmm.
The next thing to consider is the logistics of how best to fabricate with this material, but before doing so, I thought I'd ask here first in case someone has ventured down this particular road already ...