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  Osmotic Blistering - have repairs held up

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Author Topic:   Osmotic Blistering - have repairs held up
Plotman posted 02-22-2004 01:06 PM ET (US)   Profile for Plotman   Send Email to Plotman  
I'm looking for any first hand experience with repairing osmotic blisters on a whaler.

I've read the threads in the archives and the articles by the surveyor on yachtsurvey.com - what I'm looking for is a been there, done that from someone with a classic whaler. I am especially interested in whether the repairs have held up and whether you have seen any incremental blistering.

A friend has a nice 25 for sale that I'm looking to trade up to. My main concern is the blisters he mentioned. I haven't seen it yet, but I'm trying to figure out if this is something that should deter me from an otherwise nice set-up.

lhg posted 02-22-2004 01:32 PM ET (US)     Profile for lhg    
The boat must have been pressure washed. Best way in the world to blister a hull. Never do this. Used the wrong way, this is one of the most destructive devices ever invented. Trashes wood, masonry and concrete products too.
doobee posted 02-22-2004 10:20 PM ET (US)     Profile for doobee  Send Email to doobee     
Here in the Northeast, just about every boat gets pressure washed every fall and I don't see blisters running rampant.

In most cases blistering is caused by a combination of factors including, environment, materials used, and construction methods, most of which is beyond the boat owner's control.

Oversanding a new boat bottom can promote blisters because it makes the gelcoat thinner and more porous, which makes it easier for the water to get behind the gelcoat and cause the blister.

Blister repairs are successful 99% of the time. A repair failure can usually be attributed to one of two problems.

If the boat has been out of the water for a long time before the repair is done, some of the blisters may shrink and become hard to see, even though they are still there. A proper repair depends on breaking open the blisters and filling the resulting dimple with epoxy filler. The best time to start a repair is when the boat has been sitting in the water for a season. When you haul the boat, the blisters will be like plump zits waiting to pop so they will be easy to see. After you pop all the blisters, leave the boat on shore as long as possible to dry out the hull as much as possible before applying the filler and barrier coat.

The other condition that can cause a repair to fail is resin that was improperly mixed during hull construction. Since the uncured resin is buried withing layers of glass and resin, it is impossible to repair. Usually blisters caused by uncured resin are limited to small, specific areas. The only way to deal with uncured resin is to routinely inspect the area and repair blisters as they appear.

Blisters are primarily a cosmetic issue, so I wouldn't let them scare me away from a boat that is in otherwise good condition. However, if they are not repaired they can lead to more serious problems.

dreamer posted 02-24-2004 12:55 AM ET (US)     Profile for dreamer  Send Email to dreamer     
A technique that I used to remove pencil-erasure sized blisters on the bottom of the hull.
I went to Home Depot and bought the largest and heaviest chisel I could find. I then pushed the chisel at approx. 30 to 40 degrees to the surface useing light pressure and the weight of the chisel. It did an excellent job, wiping the blisters off like a lawn mower...KEEP THE CHISEL SHARP
dreamer posted 02-24-2004 01:37 AM ET (US)     Profile for dreamer  Send Email to dreamer     
After the blisters are removed.
Use a random orbital sander (that's what I used) and 40 grit paper, useing long strokes and keeping the sander moving at all times (I have short arms, so it may be short strokes for you) sand until the sharp edges of the blister holes begin to "fair" then STOP - STOP. If you don't you will end up with a big dimple, I mean a great-big dimple!
Change paper 80 grit for a few passes, but moving the sander 90 degrees from the 40 grit direction, remember, just a few passes. Then increase the grip number ending up with 320 which is good enough. All that sanding is to remove most of the scratches created by the 40 grit - not to shape the boat!! Vacuum the area clean and wipe down with your favorite solvent followed by lots of clean paper towels.
You can still see the outline of the blister holes at this time. If you can not see these outlines of blister holes.. YOU'RE ON YOUR OWN "BRO" (my disclaimer)
Now it's time to spread your favorite GOOBLYGLOB filler.
Use a piece of cardboard (thats what I used) with a spatula glob the stuff onto the edge of the cardboard, then drag it over the area of repair, holding the cardboard approx. 45 degrees to the surface and gradually tilting downward as you are dragging it. Toss the cardboard and use a new piece, continue till the area of repair is covered. You can do maybe 2 sq.ft. at a time till you've got the technique down.
Let it set. You know the routine from here. SANDING FOR SHAPING AND FAIRING.

GOOD LUCK...

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