"ruediger" wrote in message
om...
Mike Borgelt wrote in message
. ..
On Tue, 28 Oct 2003 16:01:27 +0000, Robert Ehrlich
wrote:

Miguel Lavalle wrote:

I am considering buying a second hand glider that was recently =
refinished
with poly paint as opposed to gel coat. What is poly paint? What are
the
pros and cons of poly paint compared to gel coat?

Regards

Miguel

All gliders in my club have gel coat, but our tow plane, a Super
Dimona,
has a polyurethane paint. Some of the gliders have been refinished here
in our workshop, and the quality of this finish is far better than the
polyurethane of the Super Dimona. But this quality is probably also
better than the quality of a brand new glider. A few years ago, one of
our member who had learnt the skills for doing that kind of finish was
able to convince Schemp-Hirth to sell to him a new Ventus 2c
unfinished,
arguing that he would be able to do the finish better than in the
factory, and he did it. If I understand it correctly, the main
difference
between paint and geal coat concerning the quality of the finish is
that
with paint it results mainly from work done before the painting and
with gel coat from work done after spreading the gel coat. Small
corrections
are possible with the gel coat, I remember the owner of the Ventus 2c
adding some droplets of gel coat here and there during the process
before sanding again. Small defects become much more obvious when the
surface comes near to its final state. In a similar way, minor
scratches
are easy to repair on gel coat by puting droplets of gel coat and
sanding. I don't know for paint. Also I have seen broken tails repaired
and re-gelcoated around the break with nothing remaining visible from
the
break after that. Again I don't know for paint.


The words "quality" and "gel coat"(as used currently by most of the
German glider manufacturers) should not be used in the same article.

The currently used gel coat will last a few years before cracking and
causing a very expensive refinish.

Polyurethane won't crack. Take a look at an old Pik20 or Std Jantar.

The scandal is that the cracking of the gel coat has been known since
about 1977(only a couple of years after they went to that product) and
the manufacturers flat out refuse to do anything about it.

Yes there are gel coat products that won't crack but as they "weren't
invented here" the manufacturers don't want to know.

A few people around here got Ventus 2's unfinished and had them
painted here with polyurethane.

Mike Borgelt

What gel coat product did GROB use? The finish is poor but all the
Astir's usually have no cracks. There are very few refinished Astirs.
Thank
Ruediger

All of the Twins from Grob, Twin Astir's and Twin II's, I've seen have
developed cracking on the leading edge of the wing at some point. This is
due to the gel coat being applied post wing assembly. That from the molds
seems robust.

Frank Whiteley