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post #2 of Old 02-06-2009
Jeff_H's Avatar
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I would say that this article paints a very inaccurate image of the blistering problem and is so misleading as to be dangerous.

To begin with, boats with gelcoat blisters represent a very small percentage of the boats with blisters . Most blister cases involve the laminate which occurs below the gelcoat.

In the rare case that the blisters are simply a failure of the bond between the gelcoat and the laminate, Jan de Groot is basically right that the blisters are pretty inconsequentual; remove the delaminated gelcoat, apply a barrier layer of epoxy or vinylester and the problem is gone. But that is almost never the case.

The article fails to mention the most common cause of blisters that are strictly in the gelcoat. Most cases where the blisters occur in the Gelcoat are caused by the surface of gelcoat 'going off' before the veil coat is laid up or by the surface of the gelcoat getting contaminated by wax or dust before the first lay-up occurs.

One of the key points in which this article is mistaken is the suggestion that no one has actually studied the cause of blisters in depth, when in fact there have been a number of very comprehensive studies that have been widely circulated since the studies were preformed.

These studies showed that there were a series of causes for blistering and that the seriousness of the problem is related to the cause of the problem and the extent to which the problem was left unattended to.

For example, while gelcoat is a poor water barrier, in most cases it is adequate to prevent the sub-gelcoat laminate from blistering. In the case where the gelcoat does separate from the laminate, water can get to laminate more easily and so if left unrepaired, it is more likely that the problem will spread into the laminate.

The basics of osmotic blistering, the most common cause of blistering is that by its very nature Polyester-Fiberglass matrix is porous. In osmotic blistering, water enters the pores in the matrix and mixes with the byproducts of the resin catalyzation and form compounds that attach the lay-up and destroy the bonds between the resin and laminate, which allows additional water to get to previously unexposed portions of the laminate. It is for that reason that blisters spread expodentially rather than linearly once they form.

Articles like this one drive me nuts. They sure sound knowledgeable but regrettably do not match the reality than many of us may some day have to face.


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Last edited by Jeff_H; 02-06-2009 at 02:51 PM.
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