[TowerTalk] Adding Expanding Foam inside boom

David Gilbert xdavid at cis-broadband.com
Thu Apr 26 16:01:53 EDT 2018

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.

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 at contesting.com
> Subject: Re: [TowerTalk] Adding Expanding Foam inside boom
> On 4/26/18 3:34 AM, john at 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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