Model Forum / Radio Controlled / Air Models / September 2006

 Yeah, but, how's it *sound*?  That's what counts.

Tejas Pedro

Ted shuffled out of his cave and grunted these great (and sometimes not
so great) words of knowledge:

From my own experience, Polycrylic is fuel RESISTANT provided you
follow the following caveats :

1.  Let the polycrylic dry for a MINIMUM of 7 days before exposing to fuel.

2.  Do not let the residue remain on the plane/finish for over 4 hours
or the poly will soften.

If you want/need fuel PROOF, you need an epoxy paint or one of the other
types of 2 part paints.

Martin X. Moleski, SJ Wrote:

In that case you'll need to sand the polycrylic 'cuz it's pretty slic
stuff if you get enough on the airframe to do any worthwhile fue
proofing.

Latex is gas proof, according to Vaillancourt and others, and s
doesn't need a clear coat.

You could always shoot the poly later if you swap in a glow motor.  Th
stuff isn't the cheapest thing in the world.  Half pint around here i
close to six bucks; I needed a quart to cover the 140" L-4, so th
polycrylic was more expensive than the custom blended latex I used.

One last thing - if you spray it, and it does spray quite nicely out o
the can without thinning, it _really_ atomizes, meaning that a cartridg
type respirator and fairly serious filters on whatever shop a/c an
powered air filtration system you might have are pretty much mandatory
It's almost as bad as the worst balsa dust you ever made with a powe
sander.

The white overspray dust was very noticeable in the shop air for quit
a while, and I've got a 450 CFM powered air filter with 5 mic filter
in a 10'x10'x18' shop (major overkill on air changes per hour).

The only model application I've heard of where polycrylic shines is i
glassing electrics - it's used in place of epoxy and purportedly does
good job at scant weight gain.

Personally, I'm all done with polycrylic

--
the-plumbe

Robbie and Laura Reynolds Wrote:

Latex does an admirable job of sealing fabric.

The polycrylic was intended to protect the latex from glow fuel, and
used it based on the MinWax propaganda which clearly states ". .
resistant to . . . , alcohol, and other household chemicals.".  Th
MinWas rep explained that their notion of "resistant" means if th
alcohol is diluted (as in a cocktail) and is wiped up immediately (no
ten minutes later at the end of a flight).

Having to seal the latex against glow fuel was irritating.

Having to seal the sealer is irritating-er, but I don't have a lot o
options if I want to avoid stripping the covering off a brand new 140
L-4 and starting over.

Stripping the model down to bare fabric (acetone) would solve th
polycrylic problem, but I'm not anxious to replace the 3700-odd fak
stitches that will certainly come off in the process.

I'm gonna experiment with a couple of polyurethanes which are suppose
to be fuel (in this case alcohol) proof.

If I hadn't spent the $1100 for the O.S. Pegasus engine for this mode
I'd swap in a G-38 already and get on with detailing, like installin
the 23 window panels

--
the-plumbe

I found this thread interesting as I am in the process of building a
gas powered 1/4 scale NE-1 Navy Trainer (military J3 Cub) from a Balsa
USA kit.  The covering will be Ceconite sealed with MinWax Polycrylic.
The weave will be filled with a solution of MinWax and corn starch as
outlined in  http://www.rc-float-flying.rchomepage.com/WBPV/wbpv.htm.
The finish paint will be Rustoleum as the off the shelf Sail Blue
appears to match the FS NE-1 restoration I saw at Drake Field at
Fayetteville, AR.

I have ran all the tests on an old wing section and everything worked
fine with only 24 hours of drying between MinWax and the Rustoleum coat.

the-plumber wrote:

I guess that's the difference between "resistant to fuel" and
"fuelproof".   Maybe you could take advantage of the benefits of
Polycrylic by using one or two coats to seal the fabric, and then put
some kind of top coat over it.