[NSRCA-discussion] epoxy question-I am back

Mon Nov 26 08:20:56 AKST 2007

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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