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Interlux Blister Repair and Prevention

OSMOSIS (oz-mO'sis, os-)

Dictionary definition:

The diffusion of fluids through membranes or porous partitions.

Yachter's definition:

Boat owner's greatest enemy.

Water absorbs through gelcoat causing damage and weight gain. Can be prevented with the INTERPROTECT SYSTEM.


The importance of having a moisture-free hull cannot be overemphasized. The drier the laminate, the lighter the hull, the better the performance, the more efficient fuel use and the longer the gelcoat life. A boat hull that has absorbed moisture will also sit lower in the water than intended and will reduce the responsiveness of the boat.

The INTERPROTECT SYSTEM was designed to repair hulls which have experienced gelcoat blistering. However, the best time to attack hull blistering is before it happens. Taking preventative action before a problem occurs will greatly reduce the likelihood of an expensive repair and increase resale value.

If you're buying a new boat, protect your investment with the INTERPROTECT SYSTEM before it ever goes in the water!

INTERPROTECT is a unique two-part epoxy designed to reduce the potential of water absorption by fiberglass hulls. Interprotect is unique among epoxies because it has Microplates, a protective barrier within its film to slow down water permeation. Technically, Interprotect Microplates provide millions of overlapping microscopic plates that create a barrier similar to shingles on a roof. These overlapping Microplates, eliminate any direct path for water migration and also improve the sag resistance of the epoxy making application easier.

The Interprotect Microplate Formula provides:

* Fast drying, easy application

* A barrier in the epoxy coating to reduce water damage to your hull

* Sag resistance to insure the elimination of sags and runs during application

Interprotect has been the product of choice for Boat Builders and Repair Yards since 1985.


Osmosis is a process of degeneration within a fiberglass laminate. It is caused by a chemical reaction between water and unreacted substances remaining in the manufactured hull. The water enters the hull through the gelcoat and, once inside, reacts with the chemical components creating acidic substances. These substances create pressure behind the gelcoat, which causes blisters and eventually cracking. Once the gelcoat is breached in this manner, the underlying laminate is capable of absorbing water like a sponge.

Osmosis is not only caused by water on the outside of the hull - bilge water from the inside can also cause a problem. It is therefore worth making efforts to keep your bilges dry.


Any unprotected hull is likely to show signs of osmosis eventually, like rust on a car.

The exact length of time before osmosis occurs depends on many factors, including: the type of water in which the hull is moored; the temperature of the water and most importantly, the quality of the original hull construction.

In some cases, reactive impurities in the gelcoat and laminate will cause osmosis in the early life of the boat. This is a structural problem and should be referred back to the boat manufacturer. However, even well-built, fiberglass hulls will eventually experience osmosis and blistering. This is why we recommend applying an epoxy protection layer, even to new boats.

Bottom                          Antifouling
     Blister Repair & Prevention

Interlux Antifouling Basics
How Antifouling Paint Works
Interlux Antifoulant Selection Guide
Painting Bare Fiberglass Bottoms
Antifouling Paint Systems for Various Substrates
Handy Specifications
How To Paint Previously Painted Bottoms
Interlux Applying Antifouling Advice
Antifouling Paint Calculator
Antifoulant on Aluminum Hulls
Interlux Antifoulant on Metal Outdrives, Keels and Centerboards
Hints for the Perfect Bottom Finish
Interlux Antifoulant FAQ
What is Osmosis Gelcoat Blistering
How to Recognize and Treat Osmosis Gelcoat Blisters
Protect Against Gelcoat Blisters with Interlux Interprotect
Interlux Gelcoat Blister Repair FAQ

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