[NSRCA-discussion] thinning epoxy, how?

Mon Mar 16 10:18:16 AKDT 2009

Jason

When you say finishing resin do mean epoxy or polyester? I do not 
understand your configuration of bonding the horns, but if the bond is the 
only thing holding the horns on, best use and adhesive.  Laminating 
epoxies and all polyesters have low peel strength = bad bond 
characteristics. Horns will experience a cleave stress which is 
shear+peel, if there is any flex then lots of peel stress.

A good adhesive has thousands PSI shear strength, but only 25 lbs of peel. 
Laminating resins peel = 0.

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

"J Shu" <jshulman at cfl.rr.com> 
Sent by: nsrca-discussion-bounces at lists.nsrca.org
03/16/2009 11:46 AM
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Re: [NSRCA-discussion] thinning epoxy, how?

So much good info. I'm gonna use Finishing resin to seal the motor area. 

How bad of an idea would it to be the finishing resin to glue in the 
fiberglass horns into the wood surfaces?

Regards,
Jason
www.shulmanaviation.com
www.composite-arf.com
----- Original Message ----- 
From: Gray E Fowler 
To: General pattern discussion 
Sent: Monday, March 16, 2009 11:44 AM
Subject: Re: [NSRCA-discussion] thinning epoxy, how?

Jim 

Polyesters will not cure when in contact with oxygen, leaving a sticky 
surface. If your surface is not sticky after applying-curing polyester 
then you are using a "true" polyester finishing resin, which is fine, BUT 
look out because to stop the oxygen inhibition polyester "finishing" 
resins add 5% wax, which floats to the surface and blocks the oxygen. I 
say lookout, because any future bonding to this area will be extremely 
poor. If you are not bonding to an area saturated with this resin you are 
fine. 

K&B paint was fine, just a regular epoxy cured with a polyamide, meaning 
the mixture needs to be "inducted" prior to use, that is mixed up and then 
sits in a mass for a t least 15 minutes (read the instructions) or the 
polyimide will slightly separate giving you a sticky surface. 

Unfamiliar Formula U, but Concept clear works very well. 

I always clear coat with Concept 2021..easy, lightweight and more durable. 
My entire engine area is sealed with Concept clear or laminating epoxy.

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

"J N Hiller" <jnhiller at earthlink.net> 
Sent by: nsrca-discussion-bounces at lists.nsrca.org 
03/16/2009 10:16 AM 

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Re: [NSRCA-discussion] thinning epoxy, how?

Thank you for the very informative information. I have never used epoxy 
for fuel proofing. I've used Polyester finishing resin and K&B epoxy paint 
until I ran out and recently Formula-U Polyurethane paint. What are your 
thoughts on these alternate materials? 
I find fuel proof compromising gouges are more visible using colored paint 
rather than a clear coating. 
Jim Hiller 
-----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, March 16, 2009 6:24 AM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] thinning epoxy, how? 

Fast curing epoxy adhesives such as the 30 minute are a bad initial 
choice. I realize that thousands have used it in these applications, but 
that still does not make it a good choice. The non reactive components in 
the fast epoxy plasticize with age and methanol and nitro will seriously 
degrade the stuff. Using one of the thinner slower curing laminating 
resins will require less solvent, if any and provide a much longer lasting 
barrier. Any solvent added to an epoxy needs to evaporate completely or 
you will created a problem. Denatured alcohol (ethanol) evaporates very 
slowly. Cutting a fast cure epoxy with a slow evaporating solvent is a 
recipe for trapping alot of solvent, making the chemical resistant even 
worse. Methanol evaporates much faster and epoxy is much more soluable in 
methanol. Be very careful using ketone solvents (acetone, MEK) or 
aromatics (Toluene, Xylene) because many kit manufacturers use styrofoam 
as a core material that will be destroyed in seconds with  all solvents 
except the alcohols. 

SO! 

1. Use a thin slower cure laminating resin 
2. Use Acetone, MEK or Laquer thinner 
3. NO puddles, super thin coat 
4. Alcohols if you have a styrofoam core 
5. rule #3 again 

6. If you only need the plane to last 1 year, then use 15 minute epoxy and 
do not worry..it will last 1 year or so. 

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

"J Shu" <jshulman at cfl.rr.com> 
Sent by: nsrca-discussion-bounces at lists.nsrca.org 
03/15/2009 02:15 AM 

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[NSRCA-discussion] thinning epoxy, how?

I want to add another layer of sealer to the firewall and tunnel on my 
plane... what's the best way to do it with epoxy? I've got 30 
minute but not sure how to thin it to seal it.

Regards,
Jason
www.shulmanaviation.com
www.composite-arf.com
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