Detecting and Treating Osmosis: A Guide for Boat Owners

1. Osmosis – What is it exactly?

You probably remember the process of osmosis from school. In simple terms: a liquid diffuses through a semipermeable membrane from an area of lower concentration to an area of higher concentration to achieve concentration equilibrium. Osmosis in boats, however, does not describe the process itself but the damage it causes to the fiberglass structure. A typical sign of osmosis infestation is small blisters that appear on the surface of the gelcoat. These are often filled with an acidic liquid produced by the osmosis process.

2. How do the infamous blisters form?

During lamination, different density laminate parts are initially formed, which can create small cavities. Moisture penetrating through an osmotic process exacerbates this effect. This moisture, loaded with resin residues and other chemicals, finds its way through the membranes of the laminate. The resulting pressure eventually leads to the formation of blisters on the surface. While smaller cavities can still be considered a natural process, filling larger cavities and the associated blistering represents serious damage.

3. How to tell if your boat has osmosis?

Detecting osmosis in your fiberglass boat requires a careful inspection of the outer surface. Typical signs include the aforementioned blistering, cracking, or even delamination of the gelcoat. A sour vinegar-like smell when the blisters burst right after hauling out can also be a sign of osmosis. Another way to diagnose is to check the hull for moisture using a moisture meter or special test kits. Here, it's important to choose the right settings. Often, you can select different materials and set a reference value as a baseline. This baseline is ideally located on the above-water part of the boat. Measured values in healthy material should not exceed 30 (out of 100). Anything above that can be a sign of hidden osmosis. It is important that the boat has been on land for several days or, better, weeks to avoid distortion from residual moisture. When in doubt, always consult an osmosis specialist or an expert from your shipyard before considering osmosis repair.

4. What are your options for dealing with osmosis?

Your suspicion has been confirmed; your boat has osmosis. What you can do now depends significantly on the following factors: How much time do you have? What is your budget? What is your know-how? How much work are you willing to put into your boat?

Scenario 1: You decide to seek professional help.

If your time is limited or you do not have the necessary know-how, it is advisable to seek professional help. There are numerous companies and boatyards that specialize in osmosis treatment for fiberglass boats and have the necessary expertise and equipment to effectively solve the problem. They can conduct a thorough inspection to determine the extent of the damage and offer a customized treatment solution tailored to the specific requirements of your boat. The costs range from €900 to €1100 per meter of length. Although this is very expensive, it can be the best long-term solution to preserve the structural integrity and value of your boat.

Scenario 2: You want to tackle the problem yourself.

If you have enough time, budget, and know-how, and are willing to face the challenge, you can also carry out the osmosis treatment yourself. For this, you need the right equipment and materials, especially a gelcoat removal tool, epoxy resin, fillers, and abrasives. First, you should thoroughly clean the affected area and peel off the gelcoat to expose the damaged layer. Devices like the GelPeel™ Pro enable precise removal of the gelcoat, including antifouling. If you want to avoid the high purchase prices of such a machine, there are providers like Osmosis24 that offer a device for rent. Then, the material must dry well. This happens either in a heated hall within a few days or in warm regions with the help of sun and wind within a few months. After that, the damaged fiberglass fabric is repaired and sealed with epoxy resin and fillers. This requires precise work and a basic understanding of repair techniques for fiberglass boats. It is advisable to thoroughly inform yourself about the individual steps and seek professional advice if necessary. But most importantly: don't bury your head in the sand. We have also seen that beginners were able to successfully treat osmosis when they sought good help. Regardless of which option you choose, it is important not to ignore the osmosis infestation, as this can lead to more serious damage and instability of the material. Only through timely treatment and regular inspections can you maximize the longevity and performance of your fiberglass boat.

5. Here are 7 important points to consider for DIY projects.

Once you have decided to carry out the osmosis treatment yourself, a crucial step is removing the gelcoat from the underwater hull. This requires careful planning and precision. Here are some important things to consider:

The right shipyard: Before you can start removing the gelcoat, you should find out which shipyard allows you to work on your boat yourself. Many shipyards work with companies or prohibit the use of personal equipment. Also, find out about drying options: is there a heated hall, or does the local climate allow the hull to dry in the open air?

Safety instructions: Get appropriate protective gear and wear it at all times to protect yourself from dust and chemicals. This includes gloves, safety goggles, a respirator mask, and overalls.

Preparation of the work area: Ensure that the work area is well-ventilated to minimize the spread of dust and fumes. The GelPeel™ Pro has a suction device to keep your immediate working environment clear.

Proper device settings: Make sure the gelcoat removal tool is properly set to remove the gelcoat precisely and evenly. Start with a low setting and adjust as needed to avoid over-removal.

Even pressure: Apply even pressure to the device to ensure uniform removal of the gelcoat. Avoid excessive pressure that could damage the underlying structure.

Precise work: Work slowly and precisely to evenly remove the gelcoat and avoid damage to the underlying structure. Pay special attention to areas with blistering or other signs of osmosis.

Continuous inspection: Regularly inspect the work area to ensure that the gelcoat is being removed evenly and completely. Correct any irregularities immediately to ensure high-quality work.

By keeping these points in mind and working carefully, you can effectively and safely remove the gelcoat and lay the foundation for a successful osmosis treatment. For more practical tips on gelcoat removal with the GelPeel™ Pro, read our article on osmosis treatment.