La Taberna del Puerto

[Miahpaih]

Hago Copypeguy de un comentario leido en otro foro en Jinglis, no
lo traduzco porque mi nivel no es tan bueno y porque, bueno porque
estoy un poco vaguete. Me ha parecido interesante y es algo que tarde
o temprano suele aparecer, al menos con materiales mas antiguos.
Escrito por el Sr. Kassal
Cita
-----
Jim, as you no doubt know blisters form for a variety of reasons. My personal
belief is vinyl ester resin makes a better barrier coat than any epoxy.
Epoxies absorb a lot of water and as a consequence can transmit water from the
surface to the inner laminates. The addition of fillers to an epoxy as is done
with epoxy barrier coats does not change the inherent water absorption, only
the rate of transmission. In fact I put the major brand of two part epoxy
barrier resin on my boat before her first season (new) and had blisters after
one season. I was of two minds when I did it. I'm a polymer chemist and have
some experience with epoxy resins, and had strong reservations about using the
epoxy, but I did it anyway figuring it could only help. Now I think it made
things worse.

I waited a few more years to let the blisters get fully developed and had the
hull peeled to the first structural layers. The peeled area was washed and
thoroughly rinsed to remove the dark liquids that can be present. The hull was
left outdoors over the winter with a drip strip of tape applied at the water
line. Overall it was dry enough the following spring to repair. One section of
about four square feet was still moist and I force dried it with heat lamps in
a few days.

After fairing with a vinyl ester fairing compound that was popular at the time
I did the repair by building up about .0035" of vinyl ester resin. Vinyl
esters can be thickened by adding 'Milithix' which is available (at least to a
chemist) from Milliken Chemical Co. This mix is very thixotropic and can be
built up by rolling on just three or four coats. This method minimizes the
work required of building up 10-15 coats of un-thickened resin, but more
importantly it reduces the evaporation of styrene monomer during the cure so
there is a better cure among other things.

If I were to do it again, I would add a final coat of vinyl ester that is not
thickened, but contains a bit of wax (as an oxygen barrier) and a hot catalyst
mix. I think that would make it a lot easier to sand the surface smooth.

I did my job in 1990 and have had no additional blisters. By the way I might
mention two additional things. At the time I did the job, I consulted with the
epoxy resin development manager at a major chemical company which produces
both epoxy and vinyl ester resins. He was a fellow boater and knew the resins
and issues well. He recommended the vinyl ester over the epoxy. I also checked
with some of the boat repair facilities on the upper Chesapeake Bay and found
those with the most experience and best results were using vinyl ester.

Usual disclaimers etc. YRMV.

Bob

Jim wrote:'I think the 'perfect' vessel has been found
with ONE exception - blisters . So not so perfect :-(
At the haul-out last year, in June, was the first time that the blisters
showed up
(according to the yard that has maintained since new)
all are reported to be small but covering the bottom as a Dalmatian is
spotted
The cure is - hull peel and epoxy
with 2 coats of 1000 epoxy and 10 coats of 2000 epoxy
2 coats bottom paint
Questions:
1- What % should the moisture content be before starting the epoxy
2- Is this the correct application / cure
3- any other advice much appreciated'
Fin Cita
---------

En fin escrito al parecer por alguien que estuvo alli, e hizo aquello.
Espero os pueda haber sido util.

Saludos
Miahpaih
Los hombres nacen uvas, hasta que las mujeres los pisotean y de esta
forma les aceptan una cena, pero solo como un buen vino.


_________________
Que cada arbol aguante sus levas, voto a Brios (No sé para que? Brios nunca gana)