A lot of the common expandable foams (like Great Stuff and others) are
polyurethane-based. They cure by capturing moisture from the air so
humidity is not a problem.
Dryness most certainly is. My wife and I built our home using foam
Insulated Concrete Forms (ICFs), which are like styrofoam Leggo blocks
you stack and then fill with rebar and concrete. We used spray foam to
glue the blocks together before adding the concrete, and on dry days
(i.e., spring time here in the Arizona desert) it took forever to cure.
We ended up carrying spritzer bottles filled with water to spray the
joints after we glued them. It worked like a charm. Lots of people
assume that the foam has gone bad when it doesn't cure quickly enough,
but often it's the lack of humidity that's the real issue.
So that's another problem with trying to fill a boom with foam ... the
interior might take a VERY long time to cure, although it might be
possible to mitigate that by flushing the boom with water just prior to
injecting the foam. The water adhering to the inside of the boom might
be sufficient to effect a cure.
73,
Dave AB7E
On 4/26/2018 6:20 AM, Bob Shohet, KQ2M wrote:
I would also expect that the rate and quality of the “curing” would be impacted by the
ambient temperatures and humidity levels/climate at a given location. In much of New England the
temperature can easily vary by more than 120 degrees in the course of a year – and
significantly more in the great plains states. And the climate can very enormously from the
generally wet/humid East to the desert SW. This has to have an impact.
73
Bob KQ2M
From: jimlux
Sent: Thursday, April 26, 2018 9:06 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Adding Expanding Foam inside boom
On 4/26/18 3:34 AM, john@kk9a.com wrote:
I'm not sure how you would completely fill a 12' piece of tubing with the
foam and I think it would have the potential to trap water. I like to
keep my booms completely open (no end caps).
John KK9A
the other problem is that the foam may not "cure" properly in a sealed
(or nearly sealed) container. The tesla coil community has fooled with
this to make large toroids by doing stuff like filling a truck tire
inner tube, or a ring of expandable duct, with the foam, in an attempt
to "rigidize" it.
I think the take home from all those experiences is that "it depends on
the brand and type of foam"
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