From: Brett Buck <brett.buck@lmco.com>
Subject: Re: two part epoxy finishes
Date: 09 Feb 1999
Newsgroups: rec.models.rockets

Alan Jones wrote:
>
> On Mon, 08 Feb 1999 21:08:40 GMT, Larry Hardin <hardinlw@utrc.utc.com>
> wrote:
>
> >My experience is with the old K&B SuperPoxy but the generalities will
> >still hold true.
>
> This is a good thread of info.  I have mostly used the K&B products,
> but I don't know if it has been reformulated or even discontinued.  I
> don't think it is just a pigmented epoxy resin, it is more of a hard
> enamel.  Sorta like a refrjgerator finish without having to bake the
> enamal on.  The painted surface is very hard and durable, and
> diffucult to rub or polish.  Muddy rockets clean up nice and hold
> thier gloss.

    This was the primary difference between K&B and Hobbyposy - I much
preferred the type of hard finish that K&B provided. Hobbypoxy touts
flexibility, but K&B was flexible enough. The differnce is the type of
resin used - Hobbypoxy uses something akin to Hobbypoxy Formula II
slow-set glue, and SuperPoxy uses something like HobbyPoxy Smooth and
Easy finishing resin. I have toyed with making some paint using Smooth
and Easy or West systems epoxy, pigment, and a bunch of thinner, but I
haven't gotten that desparate yet. I only use Hobbypoxy because of the
colors and then cover it with a diamond-hard urethane clear.

> What I wanted to add is that the primer is my favorite primer/filler
> material.  It is a bit inconvienient to have to mix it first, but it
> can be brushed or sprayed in thin or thick layers.  It adheres well to
> unprepared body tubes and will not tend to flake off when sanded too
> thin.  It sands easily and does not load up  the sandpaper.  For
> contest models I usualy finish with a light coat of spay dope, and
> polsih.

     K&B Superpoxy primer is/was by far the best I've ever used in any
application at any price, and I've tried a bunch. No contest, hands
down, nothing else comes close. Even smells pretty good when you are
sanding it. It never loads the paper, and sets up enough to sand in as
little as an hour in warm weather.

     K&B Superpoxy (colors, clear, or primer) is no longer manufactured.
It has been replaced by K&B Ultrapoxy. I have the Ultrapoxy primer, and
tried it for the first time this weekend.  While its not nearly as good
as Superpoxy primer, it's still a noptch above anything else I have been
able to find recently. The catalyst is the most vile smelling,
bilious-looking stuff I have ever had the misfortune to be around
(beating out Kodak Technical Pan developer, with smells like decaying
crude oil). OF course, you probably shouldn't be smelling it anyway. It
takes a good 12 hours+ to set up, and oddly it's glossy. It sands pretty
well and seems to build reasonably well. It's moderately expensive, but
so are all the others. After spending $20 for a one shot can of clear
catalyst of which I use 3 capfuls, I guess I'm jaded.

    A friend will soon be using UltraPoxy colors on a stunt plane, and
I'll report back how that works.

    Hobbypoxy primer/undercoater gets a big thumbs-down - very thin,
hard to sand, and oddly, poor adhesion. And it's also really heavy.
Don't bother, most spray can primer is better, and much cheaper.

    As an alternative to all these 2-part mixes, I have heard nothing
but glowing rave reviews of a new butyrate dope that fixes all the
reasons no one like to use it (except the smell, of course). It's made
by Randoplhs, and is distributed by Brodak's Manufacturing (a
control-line stunt manufacturer). See a link www.zianet.com/pampaeditor
and then "suppliers" to their web site.  Covers well, set up very
quickly, sands well, and has relatively low shrink. I don't have any
yet, but if it'e even a fraction as good as it's claimed and reported to
be, there won't be a need for any others. And no, I don't get a
kickback.


     Brett

From: Brett Buck <buckbw@pacbell.net>
Subject: Re: two part epoxy finishes
Date: 06 Feb 1999
Newsgroups: rec.models.rockets

"R. J. Talley" wrote:
>
> I've got a question. Whilst snooping my way through the hobby shop today, I
> discovered several racks of "hobby poxy" brand two part epoxy aircraft
> finish. The directions suggest spraying it. So, what exactly is this stuff?
> Is it an epoxy paint? If so, what are the advantages?  If not a paint, then
> what?  Also, how do I keep this stuff from ruining my airbrush? Typically,
> how fast does it cure? How long is the working time and how long do I have
> until I must clean it out of my airbrush? What do I use for a cleaner?

    Hobbypoxy is a two-part epoxy paint that has very good coverage and
is reasonably tough. Accordng to the people at Pettit (who
make/distribute it) its a slow cure epoxy glue (like Formula II) with
pigment and a lot of solvents to make it brushable. Further thinning is
needed to spray it. Note that "one part" epoxy paints (typically in a
spray can), while technically containing the epoxy resin, are not the
same and do not cure in the same sense as the two-part epoxies and glue.
Same with polyurethanes, for that matter. The advantages for airplanes
are that it is completely fuel-proof, much more so than dope. It also
has much much greater coverage, since the strong base will support a lot
of pigment, unlike dope which is notoriously thin on pigments. The
greater pigment content is generally an advantage, as long as it is
sprayed thin enough. Lots of volume in many coats like dope will result
in a tremendous weight build up.

    It sprays just fine through an airbrush with sufficient thinning. It
cleans up about like any other paint except for the fact that you do
need to clean it up completely. It is not that difficult to do - I have
used it dozens of times and never had the gun get glued together yet,
although a young friend of mine did. It was a very expensive lesson. It
can sit in a cup for quite a while - overnight at least. If you leave it
long enough, enough of the solvent will evaporate to allow the epoxy to
begin to cure, and it will eventually cure to a rubbery cup-shaped
casting.  Sprayed on thin, the solvent evaporates first and then the
eopxy cures more or less normally. Sparyed properly, it starts gettng
tacky after 15-20 minutes, stops picking up dust after about an hour,
and then needs to sit at least 12 hours to be handled - more is better.

 Use HobbyPoxy thinner to thin it for spraying, and use lacquer thinner
to clean the gun, etc., since it's cheaper. You shouldn't be too
concerned about it jamming up the gun, and you should never put the gun
down without at least spraying some thinner through it anyway, no matter
what paint you are using. It's not going to set up while you are using
it, I promise.


    Hobbypoxy brand is somewhat touchy to mix and use. It seems to
contain some plasticizers that are intended to keep it flexible over
open-bay structures. I would prefer that it cure up a little harder -
sometime it just never loses that slightly rubbery feeling. This doesn't
make it all that easy to color-sand.  I know this shouldn't work but I
habitually mix it with just a tiny bit extra "part B", and this seem to
get rid of a little of this. I have rubbed it out, but it really doesn't
take a very good shine. You really need clear for a top coat anyway no
matter what type of paint you use, if you want to really get it polished
up. The white color tends to be a little yellow, so add some blue to
compensate.

    Overall, I prefer the now defunct (damn pollution N*zis!) K&B
SuperPoxy for its handling qualities. On my last few stunt planes
(http://www.jps.net/hemanlee/bbuck.jpg), I have used K&B SuperPoxy
White, and Hobbypoxy Colors (maroon {really deep red} and blue), since I
prefer these to the SuperPoxy colors. Trim is Rapidograph 3084 ink and
Letraset, with the whole thing then clear coated with PPG DAU75 acrylic
urethane and DXR 80 hardener, with a little fisheye killer thrown in.
This clear is very tough, very hard, and an absolute magic when rubbed
out. Be sure and rub it out within about a month, or it will be very
very difficult.

     This finishing system should work quite well on larger rockets as
well. I'll let you know, as I just this very afternoon I got a fresh
supply of paint to use on a rocket. I will probably use epoxy clear
instead of the urethane, since I have some and I would have to drive
outside the Bay Area Air Quality Management District to get more
urethane hardener, and its not exactly a nice day for a trip to Santa
Cruz.

     Pettit also has a pretty good tip sheet on using their products.
Thier address is:

               Hobbypoxy Products/Pettit PAint Co,
               36 Pine Street
               Rockaway, NJ 07866


   I imagine a SASE will get you the tip sheet.

        Brett

From: Brett Buck <buckbw@pacbell.net>
Subject: Re: Airbrush help
Date: 02 Feb 1999
Newsgroups: rec.models.rockets

bob fortune wrote:
>

>
> Hey Brett,
>
> Your nose, hunh?  I was wondering what that growth was but didn't want
> to ask. : )
> (Brett and I parked at the same table at the LUNAR launch Saturday)

    Now I'm really embarrased - I didn't draw the connection between Bob
Fortune the RMR denizen, and Bob Fortune the LUNAR stalwart.

     That's the first organized launch I had been to in probably 20
years. I had a GREAT time! I'll be more prepared next month.

> I have to ask, why do you spray epoxy through an airbrush?  Do you tint
> the epoxy as a finish coat?  Do you use it for it's fast build as an
> undercoat?  A sanding sealer?  I give up.  How do you get it thin enough
> to spray or do you shoot it uncut?

    I'm sorry - not enough information. The two-part epoxy I was
referring to is either K&B Superpoxy or Pettit Hobbypoxy paint. These
are two part epoxie paints - really just normal epoxy glue, thinned out
greatly, with a pigment. They are great for my primary hobby - Control
Line Stunt. These airplanes are judged for appearance and this leads to
some pretty good finishes.  I am still learning the paint end of it, but
I have had great results using K&B or HobbyPoxy colors, covered with PPG
DAU75 catalylzed acrylic urethane clear. This is a great clear, that
will go over just about anything (like dry transfer lettering and
Rapidograph ink) without destroying it, and rubs out extremely well. It
would also be great for rockets, too. It does require a full respirator
mask, eye protection, and at least some skin covering.

     I go to a friend's house and use his tank-type compressor and an
automotive touch-up gun for the primer and base coats. I then use the
airbrush and the little diaphram compressor to do the trim colors, then
return to my friend's house for the clear.  The epoxy paints will easily
thin down enough to go through the airbrush without getting runny, and
have a tremendous amount of pigment so it covers very well. For rockets
the size I typically make, the airbrush is plenty big enough to do the
whole thing.

     If you do use an airbrush, you'll never use another spray can.
>
> Just Wondering.  By the way, your Estes Falcon gliders flew incredibly
> well! You put on quite the show for us all.

      Thanks very much - I was just hoping they didn't loop into the
ground under power in front of the crowd. The Falcon is relatively
difficult to get aligned properly, compared to more modern gliders.
Getting both wings on at the same angle is pretty difficult when you
glue the wings on opposite sides of the keel. It also creates a
tremendous weak spot- it'd be much stronger if you glued the wing roots
together.

   It also needs either pretty heavy wood, or some sort of tissue or
graphite covering on the wings to stiffen them up. It was OK on a
1/2A6-2, but developed an interesting buzz on the mighty A8-3 which I
assume was flutter. I only built those two gliders the morning before
the launch in about 2 hours and didn't have time to get too fancy.

     The performance is pretty darn good if you get them straight. I had
a high flight time of about 70 seconds with a 1/2A6-2. I would have lost
them both if the air hadn't been so dead. The weekend before I lost
three of them OOS in thermals, two on the first flights! I really need
to get some 1/4A's, or at least rig up some sort of DT. Ryburn Ross
tried to talk me into trying a C6-5, but I decided to let him try it
with his Falcon. It would be out of sight by a factor of two if it
managed to not shred.

     Brett