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From: Dave Cooper (no email)
Date: Fri Aug 03 2007 - 10:54:51 EDT
Over the years, the first was in 1974, we have done many blister jobs....in
the hundreds. These have ranged from small cosmetic blisters under the gel
coat to large structural dinner plate sized blisters that actually have
penetrated the entire lay-up.
So with such a wide range of "blister types" any one suggestion as to the
best repair method is a bit risky, IMHO. What works for one type may
actually promote furthering blistering in another type.
Always best to get an expert opinion. Unfortunately they are far and few
between. Lots of folks have promoted themselves to be so and the snake oil
flows freely to those wanting a less expensive cure.
One thing that is common is to not use a grinder of any type till you have
opened the blisters and washed them out. If they are of the simple gelcoat
variety then peeling the gelcoat with a purpose built power planner is best.
Pressure wash the hull a few times and once it is dry then the repair can
start.
If they are the deeper and larger variety then using a chisel to open them
up is the preferred way, IMHO. If you use a grinder to open them then the
"slag" from the disc is driven into the very crevices that you want to be
able to drain and dry. Once you do this then they will never drain and will
accelerate future problems.
A grinder is good to use once the blister has been flushed and dried several
times. Then the slag is not driven into crevices which still contain the
uncured resins of the production process.
The scarf ratio is always something that folks can argue about. Anything
more than 8 to one using quality no blush epoxy resin's and an appropriate
number of layers of fiberglass to rebuild the area has always worked in the
past and I've never had any issues doing this on customers boats.
As has been stated there are cosmetic blisters and then there are serious
blisters...... the first are a simple matter and you can either fix them or
not. The deeper ones do need attention as they will only get worse as water
continues to get thru the porous skin and leech out the chemicals that make
up the polyester/vinylester lay-up of the original hull.
For what its worth the best time to check a hull for blisters is directly
upon haulout. Once the hull has dried for a couple of hours many, if not
all, of them will recede as the osmotic pressure relieves itself and will be
difficult to locate. A boat that has been hauled for a long period of time
can have blisters but they cannot be detected without peeling the gelcoat in
suspected areas....not something that most folks are will to do...sort of
like a witch hunt ;-)
In summary I've not ever come across a blister repair methodology for "lazy
boaters" that actually repairs them. However we've repaired lots of these
DIY jobs. Either leave them alone or fix them correctly. If I were asked for
an opinion by a surveyor on a half a....d repair job I would suggest that
the prior work be done over and any "new blisters be repaired using the
correct method for the type of blister. So investing time and money into
work that will have to be redone isn't the best investment of your time and
money, IMHO.
As always YMMV....
Dave & Nancy
Swan Song
Roughwater 58
Caribbean Cruise '07
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