Refinishing: Who has tried a shortcut?

This thread has become very interesting…. there is considerable technical
discussion orbiting some of the comments. It would be nice if we were all in
the same room, where we could exchange a mass of information, rather than
simple RAS sound bites.

In too brief a sound bite fashion let me address a few of the comments:

The difference between boat gel coat and glider gel coat - It is a given that
boat gel coat holds up better than glider gel coat… many boat companies offer
a 10 year gel coat warranty! Boats are built with polyester gel coat and a
polyester (or vinyl ester variant) laminating resin substrate. The resulting
bond is a *COHESIVE* in nature. A previous comment was correct, that
essentially when boats come out of the mold they are finished (from a gel coat
cosmetic perspective - no sanding). The boats built today are using 4th and 5th
generation gel coat formulations that are fairly sophisticated. One small boat
company in the U.S. will use more gel coat than the entire glider industry.

Gliders, on the other hand, use polyester gel coat and an epoxy laminating
resin substrate. The resulting bond is an *ADHESIVE* force. The state-of-cure
of the gel coat applied in the mold at the time of laminate application is
critical to the bond. This is a complex interplay involving initiator level,
temperature, time, gel coat thickness, and other factors. There is an optimal
cure-state window for development of maximum bonding between the cured gel coat
and the laminate. At best, the adhesive bond between polyester and epoxy will
not produce as much energy as a polyester to polyester cohesive bond. The gel
coat typically used on gliders is the same basic 2nd or 3rd generation
technology as used on boats in the '70's and '80's. Also, there is
considerably more surface movement on a thin skinned glider laminate as
compared to a much thicker boat laminate.

Addressing a few of Ruben's comments - When gel coat is applied wet-on-wet, as
in the mold, it does cure as a uniform molecular matrix. When gel coat or a
paint coating is post-applied (as in repairs or refinishing leading edges out
of the mold) there is little, if any, crosslink bonding that occurs. This
scenario relies for the most part on a simple mechanical bond as Ruben
correctly stated.

Ah, the moisture issue….. It is correctly stated that gel coat and
composites laminates have the properties of a semi-permeable membrane. However
the discussion leaves the tracks with the idea of liquid water penetration and
surface porosity. *Water vapor*, that is individual molecules of H2O, will
continually seek to equilibrate on the inner and outer skins of a laminate in a
very slow process. Water in the liquid state will *not* penetrate gel coat.
The surface pores and voids in the 3-D molecular matrix are too small for
liquid phase water to penetrate. This has to do with the inherent surface
tension of liquid H2O. The surface does not wet enough for liquid to flow into
the normal porosity.

You *do not* have to be concerned about washing your glider with water, or
leaving it out in the rain for that matter. It will not have a negative effect
on the gel coat. Wax does not seal in water. Vapor phase H2O will freely
equilibrate with no noticeable retardation of transmission through a wax film.
Additionally, since liquid water is not present within the gel coat or laminate
matrix, (under normal circumstances - let's not talk osmotic blisters), there
is no issue with freezing and causing cracks. This could become an issue with
giant cracks, but not with typical gel coat effects. Freezing water is simply
not an issue.

Again, hope this helps…. After 38 rounds this thread has stayed coherent….
has to be a record for RAS!

Bob Lacovara