osmosis -> is this true?

[Karletto]

i heard that people don't cure osmosis/ osmosis bubbles anymore; in the past boat owners called an expert to cure/ repair the hull => big $$ but now there's a theory that is "better" to leave it/ not dangerous as people say and spare money (even with hard ones)

[S/V Illusion]

Blisters are often a source of controversy among the "experts". Some "experts" say it's fine if they are small in size and number to do watchful waiting and if they don't permeate the glass, do nothing. Others have a fit over them regardless of size and number and insist the structural integrity is being destroyed. The truth is, as you might expect, somewhere in the middle and if you are unsure, it would probably be wise to find someone with experience who you can trust to take a look to see which category your's fall into.
In either case, the effort require to fix is directly related to size/number but not outside the ability of most people to repair themselves once you know how and the ability required to apply an epoxy barrier coat to preclude recurrence is equivalent to that of a house painter who can read directions.

[AnchorageGuy]

As a Yacht Broker for a long time I dealt with blister issues more than I can count. No vessel has ever sunk as a result of blisters. And be careful because blisters and delamination are two different animals. You can really take them or leave them. The problem really comes up when you plan to sell the boat and the potential buyer freaks.

[sabray]

It depends on the hull construction, level of damage and the quality of the repair.
Osmosis is the resin being disolved by water. A blister is the result of a chemical reaction between resin and water. Simplified water passes through a screen that is gel coat it mixes with resin and molecules expand but the screen it now to small to allow the molecules to permeate and the pressure from the reaction causes the gel coat to bubble. Osmosis can be present with out blisters. If the screen is large enough to allow the expansion with out development of pressure. Often you will hear my old boat never had blisters. Correct but it probably had osmosis.This can't be good. also it may not be that bad.
Old hulls that were built before the limitations or possabilities were understood have glass and resin at levels that may be assumed sacrificial. As the cost of resin increased and understanding improved boats became lighter and resin saturation levels decreased. Some resins were developed to have different properties. One such resin was fire reatdent but also was very soluable. lightly built hulls with reduced resin ratios, cored hulls, poor layup could have and I have seen significant weekening of the structure.
A superficial repair without proper removal or drying of the hull has limited benefit. If you are really concerned you should get a surveyor that understand the lay up schedule of your boat and can analyze the extent of damage and rate of deteriation. The inspection should included a density test and the test should be performed at layers until a suitable reading is obtained moisture tests are good as are visible inspection of the laminate condition.

Hope this helps