Rudimentary question about blisters
- Thread starter Project_Mayhem
- Start date
Gosh Judy, I'd have to go back and look. I googled a few articles talking about osmosis and found one that had a pretty good section on various aspects of it. If you really want me to let you know I will see if I can find it again and answer your questions. The Delta P is pressure. I'd have to look at the others but it's late on this side of the continent and I'm heading to bed.
dj
There ain’t no such thing.To prevent it, you need a barrier that is not permeable to water.
Neither vinylester nor epoxy resin nor inter protect 2000E are impermeable to water.
Correct. In fact there are very few impermeable substances; stainless steel, OFC copper, quartz (specific types), a very few ceramics, to name some. But polymers, epoxies - none.
dj
Was it really stripped to the bare glass as you said in the original post? Or was just the built up paint stripped down to the gel coat, which would be more typical?
The vast preponderance of blister form at the interface between the gelcoat and the outermost layer of fiber. These are rarely of any structural consequence. Based on articles written by a couple of surveyors that I have read over the past thirty years, more than 95% of all cases of boat blisters occurs in the gelcoat/laminate interface.
Usually the outermost layer of glass is a thick layer of mat, which too frequently suffers from having been incompletely saturated with resin. The dry fibers wick water along them which Promotes hydrolysis of the ester bonds. the by-product of bond hydrolysis is an acid salt. This then attracts water via osmosis, which causes the characteristic appearance of a blister in the gelcoat, which is simple plastic that isn’t reinforced with fibers. So the gelcoat bulges out under pressure.
Mat was traditionally used as the first layer of laminate just below the gelcoat be cause woven roving shows through the gelcoat. Mat is smoother and doesn’t show through. However, It’s more work to fully saturate mat, than woven cloth as those of us who have worked with it a bit can attest.
A very few cases of failure occurs deep within the laminate. Large pockets filled with acidic solutions occur, resembling delamination more than blistering. In virtually all such cases, according to the surveyors I’ve follwed over the years, this occurs next to glass fibers that weren’t wetted with resin. I’ve seen a few examples of this myself, when I cut away laminate that had delaminated, and found a layer of dry glass fiber. ( dry in the sense of without resin)
Hand layup is better than chop gun layup, but only if the technician does a careful job. These days I’m doing pressurized layup and vacuum infusion where ever it’s feasible.
Judy
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In some spots where the bottom paint is worn away you can see a smooth, manila colored surface. The gelcoat above the waterline is white and off white. These little craters are less than 3/16" wide. I do not believe they are structural in any way. I assume it does affect top speed
The O'Days of this era are hand laid. I've found a few small voids here and there but nothing that really stood out. Are you building a boat from the hull up?