You see this quite often in internet
discussions, I call it the SOTF (Sliver Of Truth Factoid). In focusing in on the vapor barrier physical properties of “polyester” (to keep the argument technically correct but practically meaningless) as Tera Nova is missing the larger picture.
Sure polyester alone isn’t a true scientific vapor barrier, who doesn’t know that? But the other Ĺ of the story being left out is, do you ever have just a polyester/fiberglass box and just how good of a vapor barrier is it? Of course Q1 is no, no one’s box is just pure polyester and glass, there is gelcoat
on top of it. So quoting the physical properties of polyester scores techy points in a forum, but how useful is that point since I’ve never seen an ice box made out of glass and polyester? They all have the added vapor barrier of gelcoat
. So then how good is it and is it good enough? Are we 50% as good? 90% as good? How does that factor into the Cost/Good enough curve? When I've cut into boxes reinsulated using this simple/cheap approach 10/15yrs later and found them still good...what are we arguing about for $200 in materials and a weekend of labor? How many angels can dance on the head
of a pin?
What kills insulation…air movement around it that brings moisture and said moisture then condenses and if it gets into the foam it wets it and then ka-bash…the foam is worthless. So that’s where my “crazy” comments comes into play because how much better is an epoxy
true vapor barrier than the ice box tub the cruiser has now? Is that degree of improvement worth the work/expense? Not to most people it isn’t.
I shouldn’t be as much of a smart ass as I am…it’s probably not good for “business” as my wife says, but hey, my sense of humor
is what it is and it’s taken me this far as a Cruising Bozo. I’m not trying to knock Tera here his box is probably a dream case box and a thing of beauty. I'm trying to point out that when discussing techy things, the one line data points without discussion behind them can cause more harm than good. Every thread about box insulation
makes it sound like if you do anything but poured foam, aerogel or VIPs then you are doing it wrong and a screwing up....I call BS on that.
For example, a guy with a classic plastic bath tub ice box. Is he better off adding 1-2” of PolyIso insulation
to the inside of his box, covering it with fiberglass
board from home depot, caulking the seams and then getting his ass out cruising with a improved box to cut down on power usage at a cost of less than $200. OR do we tell that guy that the only way to go here is to rip out his box and pour closed cell foam, use Vacuum panels
, or some other expensive solution that will give him what…how much better a solution? Sure in the ideal world of time/money, rip it all out and do it “right” by NASA standards. Build a new counter top and galley
counter while you are at it! But that isn’t what most people have the time/money/stomach for. Adding a few inches of polyiso to the inside of a crap insulated box is sure low hanging fruit to pick and toss at the emperor that has no clothes.
This is also what happens when I'm in the boat yard with projects lined up...I keep looking for something else to do rather than all the prep work for laying a new epoxy/glass true vapor barrier on my deck
in preparation for KiwiGrip.