[NSRCA-discussion] epoxy question-I am back

Mon Nov 26 18:49:59 AKST 2007

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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               [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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