Paul,

I agree that this additional surface work could lead to, down the
road problems. I do not think this is because of changes in the
crosslinking, at least not entirely. Crosslinking is the bridging of
the loose ended polymer chains. By designing the polymer of choice (in
this case gelcoat) to undergo crosslinking you create one giant
supermolecule. And during the painting process as long as each
additional coat is applied before the crosslinking is finished, each
additional coat will add to the matrix. But after the fact this
chemical reaction will not take place to the same extent and a
mechanical bond becomes the order of the day, hence the surface
roughing requirement during repairs.

*As a side note: the amount of crosslinking involved plays a large
part in the amount of flexibility a finish will have. By using a flex
additive you can inhibit the crosslinking in some or all of the paint.

My company's work with interfacial chemistry has long shown however,
that like a lot of polymers, even gelcoat is semi-permeable to water.
So, for example when you wash your glider, then dry it and finally wax
it (because it is all clean now, right?), your drying was never really
able to extract the water from the pores. The wax seals it in and
capillary action along with other hydroscopic forces pull (or drive)
the water in deeper where it freezes and expands, pushing against the
sanding scratches which now become stress risers, ultimately leading
to microcracks which propagate to larger cracks. Without the wax the
water is free to go, to and from, as external and internal forces
change usually in relationship to the seasons or prevailing weather
conditions.

Reuben

Paul Gaines wrote in message ...
One of the main reasons our gelcoat gliders crack up is because of the =
final finishing process. Boats are popped out of a shiny mold and are =
basically done. Glider pieces that are gelcoated get additional sanding =
for contouring, etc.. This breaks up the surface gelcoat which, at the =
time of process, has additional "protective" cross-linking at the =
surface. This is great for contouring, but a no-no for finish =
longevity...unless you immediately paint over this surface with poly =
paint, etc..

I have noted several gliders that were refinished with poly paint where =
all of the old crazing was not removed. One $10K, 2-seater refinish job =
has cracks returning after 3 years.

Paul=20