We offer complete boat blister repair services.

This hull needs boat blister repair
Damaged boat ready for boat blister repairs

Osmosis, the main cause of fiberglass boat blisters, can destroy a yacht’s fiberglass laminate.  Osmosis allows a chemical reaction between water and unreacted substances remaining in the manufactured hull. It causes blistering and delamination.

The Problem:

Water enters the yacht’s hull through the gelcoat. Once inside, it reacts with the chemical components in the resin to create acidic substances. In turn, these substances create pressure behind the gelcoat, which causes blisters and eventually cracking. Once the gelcoat fails, the underlying laminate absorbs water like a sponge. Then, boat blister repair becomes necessary.  Left untreated, accumulation of a large number of blisters will eventually create a serious hull delamination. The degree of structural damage will increase as the blisters fracture and penetrate deeper into the layers of the hull.

Osmosis comes not only from water on the outside of the hull. Bilge water from the inside can also cause a problem. In fact, any unprotected hull part will likely show signs of osmosis eventually, like rust on a car.

The exact length of time before osmosis occurs depends on many factors.  First, the type of water in which the hull floats.  Second, the temperature of the water can affect blistering. Finally, the quality of the original hull construction really matters.

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

Warning Signs:

Blisters rank as the most common warning sign of osmosis problems. Blisters can vary from small pinhead blisters, to areas as large as the palm of a hand. The presence of any fluid behind a blister indicates a potential boat blister repair problem. Fluid with a pungent, vinegary odor, or that feels greasy or sticky when rubbed between the thumb and forefinger, suggests osmosis. Before attempting any boat blister repair, you must to establish what has caused the problem.

Star Crazing – This effect can occur where the gelcoat is brittle. Fine cracks usually form due to severe flexing or impact damage, allowing water to seep into the laminate.

Pinholes – Tiny bubbles present in the gelcoat reduce its effectiveness and promote rapid water absorption.

Prominent fibers – Seen protruding beneath or through the gelcoat and can cause “wicking” where water is drawn into the hull by capillary action.

In many older vessels you may only see crazing or cracking of the gelcoat. You may never see a blister. In this scenario, the gases created by water reacting with resins simply escape through the lesions in the gelcoat.

The Boat Blister Repair Solution:

First, we identify the source and scope of the problem.  Then, we determine the depth and severity of the damage. Boat blister repair may require simply grinding out the affected area, and filling and fairing with epoxy laminate and fillers. We use an electronic moisture meter.  With it, we can determine whether the problem is localized, or affects the entire wetted surface.

If a large portion of the hull is affected, boat blister repair generally requires removal of all gel coat and perhaps even a thin layer of the underlying fiberglass. We use a specially designed peeler. Then, we sand the affected surfaces.

We dry the yacht’s hull by keeping the boat dry and out of the water for several months to a year, to allow the moisture to evaporate from the hull. Too many inexperienced boaters (and yards) grow impatient. They attempt to finalize repairs without allowing the fiberglass to dry out properly. This can lead to entrappment of moisture in the hull. Of course, this will result in premature failure of the repairs. Trapping moisture in the hull will diminish the new coatings’ adhesion to the hull, but may allow for continued blistering.

Finally, if we must remove more than 80 mils of material during peeling, the vessel will usually require a new laminate. Anchors Away recommends Interlux epoxy resins and laminates, followed by appropriate mil thicknesses of a barrier-coating epoxy product such as Interprotect, PetitProtect, or Sea Hawk’s Tuff Stuff. After applying these products to at least a 6 mil dry film thickness, we apply two coats of antifouling paint to complete the boat blister repair job.