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Go Back   SailNet Community > On Board > Gear & Maintenance > Best way to remove barrier coat
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Thread: Best way to remove barrier coat Reply to Thread
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Topic Review (Newest First)
06-17-2010 04:33 PM
cormeum
Quote:
Originally Posted by CharlieCobra View Post
Oh Joy suffered from electrolysis of fasteners only 18 months after being refastened due to a very hot marina. The owners at that time decided to refasten one last time and chose C-Flex over other sheathing methods to protect her from both marine borers and having to refasten again, with all of the issues that would entail. Unfortunately, going with canvas over ply in the traditional fashion for the deck, subsequent substandard maintenance, repairs and after they sold her, a total lack of maintenance, caused her current woes from topside fresh water leaks.
Nuts.
06-17-2010 02:37 PM
CharlieCobra Oh Joy suffered from electrolysis of fasteners only 18 months after being refastened due to a very hot marina. The owners at that time decided to refasten one last time and chose C-Flex over other sheathing methods to protect her from both marine borers and having to refasten again, with all of the issues that would entail. Unfortunately, going with canvas over ply in the traditional fashion for the deck, subsequent substandard maintenance, repairs and after they sold her, a total lack of maintenance, caused her current woes from topside fresh water leaks.
06-17-2010 02:19 PM
cormeum
Quote:
Originally Posted by CharlieCobra View Post
I can't see the need for a barrier coat on a wood boat. Anything else, yes. Wood? No...
Talk to Bob Derecktor. he smeared it the first time so he must have had some ideas as to why. I can see that it would moderate the rate of transpiration so it's not necessarily a bad thing- why did they C-flex Oh Joy?
06-17-2010 01:30 PM
CharlieCobra I can't see the need for a barrier coat on a wood boat. Anything else, yes. Wood? No...
06-17-2010 11:41 AM
cormeum
Quote:
Originally Posted by RichH View Post
Jeff -
Im a Physical Chemist, among other things. Ive observed over the years that the manufacturers recommended thickness of applied barrier coats has greatly increased over the past 20-25 years. Vapor permeability is dependent on 'thickness' of the epoxy barrier and those barriers applied 'in the earlier years' of relatively 'thin' recommendations have or are beginning to fail; the 'rate' of vapor permeation dependent on the average temperature of the ambient water. Once the water vapor 'can' penetrate there are 'many' causes for the vapor to 'stay behind' the barrier - chemical, mechanical, etc. but the principal mechanism seems to be 'discontinuous' lay-up where there are bonding discontinuities due to 'curing' between the laminate layers ... the action of simple hydrolysis of the internal structure; hydrolysis being equivalent of 'rusting' of (vapor porous) polymers.
THICK barrier coats better retard the vapor permeation; thus, better protecting vs. the inevitable 'hydrolysis'. In industry, FRG tanks that are laid-up in a single continuous process have much better resistance to hydrolysis damage and therefore last longer and with minimum 'blistering', etc.
For my purposes then, thin is better- I need some permeability as the planks will still need to take up.
I may have to deal with a lot of things, but fortunately, blistering is not one of them.
06-17-2010 09:46 AM
RichH Jeff -
Im a Physical Chemist, among other things. Ive observed over the years that the manufacturers recommended thickness of applied barrier coats has greatly increased over the past 20-25 years. Vapor permeability is dependent on 'thickness' of the epoxy barrier and those barriers applied 'in the earlier years' of relatively 'thin' recommendations have or are beginning to fail; the 'rate' of vapor permeation dependent on the average temperature of the ambient water. Once the water vapor 'can' penetrate there are 'many' causes for the vapor to 'stay behind' the barrier - chemical, mechanical, etc. but the principal mechanism seems to be 'discontinuous' lay-up where there are bonding discontinuities due to 'curing' between the laminate layers ... the action of simple hydrolysis of the internal structure; hydrolysis being equivalent of 'rusting' of (vapor porous) polymers.
THICK barrier coats better retard the vapor permeation; thus, better protecting vs. the inevitable 'hydrolysis'. In industry, FRG tanks that are laid-up in a single continuous process have much better resistance to hydrolysis damage and therefore last longer and with minimum 'blistering', etc.
06-17-2010 09:20 AM
CharlieCobra
Quote:
Originally Posted by cormeum View Post
Hey Charlie, How would you get Interprotect (or something like it) off a wood hull? Sand or heat gun and scrape?
Most epoxies are immune to strippers but a heat gun and scraper will remove it. Follow with sanding afterwards but be careful not to remove too much wood or put flat spots in it. I hope ya have some good long boards....
06-17-2010 09:12 AM
Jeff_H Moonie asked me to comment on my earlier post. Like most people who have been into boats for a while, at some point I became very concerned about the whole the blister issue. I began reading everything that I could lay my hands on which discussed the causes and cures for blistering. What became very apparent was that there were a whole range of causes for blistering, some fairly benign (such as poor adhesion between the gelcoat and the laminate) and some very dangerous to the overall structural integrity of the boat.

In this last category are issues which are directly related to the formulation of the resin or additives such as accelerators mixed into the resin by the boat manufacturer. These last set of causes vary from a slow loss of ductility in resins allowing micro fissuring, and a range of other causes which include continued chemical processes within the laminate.

According to my readings in this second case, there can be a variety of chemical reactions at work. In some cases there are larger than normal trace amounts of water soluble materials that are formed as the byproducts of the reaction or suspended in un-reacted resin.

In those cases these water soluble chemicals can react with the water to form acids or else leech out over time and leave the resin more pourous than it initially was thereby allowing water molecules to get further into the laminate and allowing hydrolysis and the formation of acidic fluid deeper in the laminate than it might form otherwise. This was cited as one possible cause of deep blistering occuring in an older boat which had not experienced blistering earlier.

In at least some of the articles that I read, heat was seen as posible cause of later onset blistering and deep blistering. In my reading, I came across several case studies that discussed boats that were taken blister free from cooler water to the tropics and immediately began to have blister problems. My recollection is that even small amounts of heat can cause an accellerated reaction of some of the previously unreacted resins thereby forming water solubles and or microfisuring within these portions of the laminate.

In some of the discussions that I read, as a part of the research, the blistering process was purposely accellerated by soaking the laminate in warm water.

I am not a chemist and have not actually done any primary research on these theories, so I personally cannot tell you whether these theories are accurate, but to the best of my recollection the articles where I read these theories were either based on practical experience for the most part appeared to be science based. If someone has a better source of information on the relationship between heat and blistering, I would certainly be interested in being corrected.

Respectfully,
Jeff
06-16-2010 04:12 PM
cormeum ...
06-16-2010 03:11 PM
deniseO30 It's so cute to hear guys talking about the their bottoms for a change !
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