[NSRCA-discussion] epoxy question

Jay Marshall lightfoot at sc.rr.com
Tue Nov 27 09:02:00 AKST 2007


Although they are self serving, these comments from West are interesting:

"There are epoxy-based products specifically designed to penetrate and
reinforce rotted wood. These products, basically an epoxy thinned with
solvents, do a good job of penetrating wood. But the solvents compromise the
strength and moisture barrier properties of the epoxy. WEST SYSTEM epoxy can
be thinned with solvents for greater penetration, but not without the same
compromises in strength and moisture resistance. Acetone, toluene or MEK
have been used to thin WEST SYSTEM epoxy and duplicate these penetrating
epoxies with about the same effectiveness. If you chose to thin the epoxy,
keep in mind that the strength and moisture protection of the epoxy are lost
in proportion to the amount of solvent added." 

"There is a better solution to get good penetration without losing strength
or moisture resistance. We recommend moderate heating of the repair area and
the epoxy with a heat gun or heat lamp. The epoxy will have a lower
viscosity and penetrate more deeply when it is warmed and contacts the
warmed wood cavities and pores. Although the working life of the epoxy will
be considerable shortened, slower hardeners (206, 207, 209) will have a
longer working life and should penetrate more than 205 Hardener before they
begin to gel. When the epoxy cures it will retain all of its strength and
effectiveness as a moisture barrier, which we feel more than offsets any
advantages gained by adding solvents to the epoxy."

 

 

Jay Marshall 

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Koenig, Tom
Sent: Monday, November 26, 2007 11:44 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] epoxy question

 

Gents and Linda

 

For laying up work, that is fuselages, cowls etc I use LC3600 Resin. I post
cure at 80 Degrees C for 4 hours. I quite like this resin.

 

For wings I sand like crazy ( both sides) and seal with dope. Honeycombed
cores. Then I use West 105/207 for skins. Never tried to post cure the
wings, I figured this epoxy would not benefit from it ( i.e I had no data
for it..so I didn't!)

 

Tom

 

 

 

  _____  

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Lance Van
Nostrand
Sent: Tuesday, 27 November 2007 2:48 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] epoxy question-I am back

I use the West system all the time but we use custom blends made up by
master Fowler for AeroSlave parts after all our R&D on the process design.
West 205 hardener gives about 925 cps and the 207 gives about 750.  The thin
stuff Gray is talking about is half that!

--lance

----- Original Message ----- 

From: Pattrnflyr at aol.com 

To: nsrca-discussion at lists.nsrca.org 

Sent: Monday, November 26, 2007 11:20 AM

Subject: Re: [NSRCA-discussion] epoxy question-I am back

 

I have built several wood racing boats with West System.  The 105/205 is for
gluing and the 105/207 is for glassing and is much thinner and easier to
work with.  I glue the boat together with 105/205 and then roll on 105/207
for the final finish and you are done.

 

Bruce Reins
A Stock Hydro/Runabout
15-R 

 

In a message dated 11/26/2007 8:46:44 A.M. Mountain Standard Time,
lightfoot at sc.rr.com writes:

West's 105/205 system seems to be a low viscosity epoxy. It is a slow cure
(8 hrs) so if you add solvent it should have plenty of time to evaporate. I
have only used it for sheeting, not glassing - yet.

 

Jay Marshall 

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Gray E Fowler
Sent: Monday, November 26, 2007 10:23 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] epoxy question-I am back

 


1.  "Thinning the epoxy saves no weight by evaporation.  There is virtually
no evaporation and no weight loss-a big time erroneous assumption on my
part.  So if you mix 2 ounces of epoxy and add 2 ounces of thinner and put
it all on the airplane, you have added 4 ounces to the airplane.  " 

After seeing the real question I expected a weight increase of at least 9%
(how much water in the mix). If you put 1oz (by weight) of solvent in 1 oz
of epoxy, and apply it as a coating , thin, you will eventually end up with
1 oz of epoxy. Mike, your solvent got trapped, and now it will have less
adhesion, less tensile, Compression and flexure strength, and will now
shrink slowly as the alcohol exits the cured epoxy, over a year or so (see
Wayne's answer). 

None of the solvent's listed will react with any epoxy blend. Exotherm is
negligible when applied as a thin coating, but significant in mass. The
ability to have the solvent evaporate out of the epoxy coating is directly
related to the mixed viscosity of the neat epoxy blend and the cure rate of
the epoxy. Those of you who ran experiments with 5 minute epoxy reported bad
results because of high viscosity and fast cure rate.The high viscosity
(even Mike's blend is apparently too high) will cause a skin effect where
the solvent evaporates from the surface first, creating a high viscosity
skin, then the epoxy starts to cure increasing viscosity even more, thus
trapping the solvent. Using fiberglass makes this even worse. MIKE- in one
year from now your wings will weigh less. 

So it sounds like the the Pattern Dudes of the world need a solution.  What
AeroSlave can do is provide a super low viscosity epoxy for sale. This will
be 100% solids (which means NO solvents). Chances are, as a mixed epoxy, the
viscosity will be lower than even blends with some solvent in them. This can
be used to apply fiberglass to wings or as a general laminating resin. 

How much interest would there be for such a a product? It would probably
cost about $50/ quart, $25/ pint. It would absolutely require an accurate
scale (+/- 1 gram) to WEIGH the epoxy and hardener into the appropriate mix
ratio. AND I offer no warranty, simply because you guys are the biggest
bunch of experimenters in the world, and I cannot control, nor anticipate
how this could get screwed up. 

1. Operator cannot operate a scale. 
2. Operator has a crappy scale. 
3. Operator added solvent anyway because thats how he has always done
it...since 1976 
4. Operators basement is 100% realative humidity..condensation on the wing. 
5. Operator added "more" hardener to make it cure faster. 
6. Operator......(enter F/U here). 

As you can see there is one common theme to all of these possible problems,
Operator, i.e. customer. 

So if you are STILL interested please respond and Lance and I will take it
under advisement. 

  



Gray Fowler
Senior Principal Chemical Engineer
Radomes and Specialty Apertures
Technical Staff Composites Engineering
Raytheon 


"Dr. Mike Harrison" <drmikedds at sbcglobal.net> 
Sent by: nsrca-discussion-bounces at lists.nsrca.org 

11/23/2007 01:57 PM 


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Subject

[NSRCA-discussion] epoxy question

 


 

 




I have read with interest all the comments and some of you have educated me
on this issue.  If I may, I will share what I have learned. 
  
1.  Thinning the epoxy saves no weight by evaporation.  There is virtually
no evaporation and no weight loss-a big time erroneous assumption on my
part.  So if you mix 2 ounces of epoxy and add 2 ounces of thinner and put
it all on the airplane, you have added 4 ounces to the airplane.   
2.  The properties of the epoxy are changed-it becomes rubbery. 
3.  Changing the properties is not an issue regarding finishing the
airplane(painting) 
4.  Using thinned epoxy is fine for applying glass cloth. 
5.  I have tried MEK(epoxy thinner), denatured alcohol, 91%alcohol, acetone.
My preference is denatured alcohol because it is the safest and most
economical, I think.  I thought MEK would be the answer.  It is the worst of
the bunch.   
6.  The best way to glass surfaces is to thin the epoxy and apply as
sparingly as possible.  A way to do that is to apply and wipe off excess
with paper towels.   
7.  It is almost exactly 2 ounces to glass a wing panel complete, so 4
ounces for a whole wing.  About 2 ounces for a stab.  Properly done wings
and stab glassed and painted is 2-2.5 times the weight of monokote.   
8.  A second thinned coat of epoxy on the glassed wing is .75 ounces each
wing panel-1.5 oz total. 
  
  
Pick your poison. 
  
Later, 
Mike 
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