[C38] Hull blistering - ouch!

[tdtron at earthlink.net]

Hello Marci,

Our 38 was blister free but we had blisters on our Catalina 27 in the late 80's when I was racing it.

I hauled the boat, draped a tarp over it to keep any rain off of the hull while the hull dried, and I then sand blasted each blister down to the substrate.  Very small blisters become craters with a sand blaster but like getting teeth cavities filled, it's important to completely clean out the void.  Even though the hull had dried for several days, most blisters produced liquid when they were lanced with the sand blaster.

I filled each blister with MarineTex filler, sanded them smooth, and then coated the whole hull with an epoxy barrier coat before applying the final anti fouling bottom paint.

MarineTex is hard to sand once hardened but if you smooth the filler when you apply it, you minimize sanding later.

Over 22 yrs later, our 27 still has no blisters.

I haven't kept up with the products on the market today but I think the most crucial thing is properly cleaning out the blisters.  If you paint over blisters they will just pop up again, much like painting over rusty metal.  I've seen people try to clean out blisters with a Dremel type tool but I find the sand blaster works faster and better.  I've located blisters by hitting the hull with a sand blaster and cavities popped out where none was suspected.  Those areas would have been pronounced blisters left unchecked.  The Dremel type tool can't poke through the gelcoat and find unsuspected cavities like the sand blaster can.

As a bit of trivia, I have heard that blistering is most common on boats built in the hot summer months.   The theory is that layup is a hot and demanding job and usually reserved to the new hires at most boat manufacturing plants.  The factories are un-preconditioned and protective clothing makes it all the hotter for the worker.

As they workers perspire, sweat drops hit the molds causing localized poor hardening of the resin where the drops land.  If the sweat drops hit between layups (schedules) it can also cause de lamination.  Most layup workers are made to wear disposable paper jump suits but when it gets really hot, those paper jump suits get saturated with sweat causing sweat to hit the layups like rain.  Polyester resin is especially sensitive to sweat contamination.  The good news is that if you find and repair each blister properly, they usually don't return.

Anyway, that's my experience.  I'm sure there are others here who can elucidate on this subject better than I can.


Tom Troncalli
recovering ex-Catalina 38 owner



----- Original Message ----- 
From: Marci Brown 
To: listserve at catalina38.org
Sent: 5/2/2011 8:56:30 PM 
Subject: [C38] Hull blistering - ouch!


I just discovered a few blisters on our hull. Would anyone like to share their experiences with this dreaded subject matter?
 
Marci J. Brown
PO Box 520549, Winthrop, MA 02152 USA
Ph: 757-515-3151 | Email: mb at seafor.us



 
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