Preventive anti-osmosis treatment for polyester boats

In this article, we explain step by step how to go about DIY osmosis treatment and how to ensure your boat remains osmosis-free. Osmosis on boats and yachts has a self-reinforcing effect. Extreme cases of osmosis can eventually cause delamination of your boat, which reduces the strength of the hull. When you treat osmosis in time, you maintain the strength of the hull and osmosis treatment will be easier. You can easily perform an osmosis treatment yourself using this step-by-step plan.

Osmosis Check

Prevention is better than cure and we therefore recommend regularly checking both old and new boats for osmosis. That way, you can treat osmosis in time. 

Requirements for an osmosis treatment

The quantities of the supplies below depend on the overall size of your boat's hull. If in doubt, please contact us for tailor-made advice. 

For this job you need various raw materials and tools. If you order the items below at Polyestershoppen.com, they will often be shipped the same day so you can get started quickly!

Commodities

Tools

Step 1. Remove the gelcoat layer

First, the boat's hull must be exposed. To do this, the gelcoat must be peeled back to reveal the polyester fibers. This can be a tedious job, but once you have done this, the worst is behind you. You can remove the gelcoat with a Gelplane vacuum scraper or, for example, an angle grinder with a flap disc. Gelcoat removal is even faster with the professional Tercoo rotating blaster with adjustable guide and dust cover. You can also hire a company to remove gelcoat on site.

Step 2. Clean and dry the polyester laminate

When you have removed all the gelcoat, it is important to regularly clean the surface of the bare laminate with clean water and to let the laminate dry for at least a few weeks, for example throughout the winter. It is not a problem if the ship remains slightly damp, but the drier the better.

Polyester boot met osmose kaal

Polyester boot met osmose kaal

Step 3. Fill/smooth the underwater hull

When the laminate has dried sufficiently, you can smooth the hull with International Watertite epoxy putty. Watertite is extremely water-resistant and is easy to apply due to its 1:1 mix ratio. You can also use homemade filler made of fast epoxy resin combined with red microballoons. Read more about smoothing the boat's hull here.

Now clean and degrease the surface well with acetone before continuing.

Step 4. Apply two layers of epoxy twill fabric

Now you will apply two layers of twill fabric and epoxy. Epoxy from Polyestershoppen.com does not contain any solvents and is therefore completely vapour-tight when processed properly. Apply the fabric with several people. Someone cuts the fabric and applies it to the boat, someone else rolls epoxy over the hull, for example.

After you have cut the fabric to size, epoxy resin can be applied to the entire hull. This can be done with a velour roller. Always wear nitrile gloves when processing epoxy. After applying the resin, the fabric can be applied to the boat hull. Then roll epoxy over the surface and de-aerate the laminate with a de-aeration roller.

You can overlap the pieces of glass fabric by about 2 cm. Work from back to front so that the overlap is in the most common sailing direction. 

When you have laminated the entire hull, we recommend covering the surface with a layer of peelply. This tear-off fabric prevents a wax layer from forming on the epoxy and you needn't sand the boat when you are going to apply the coating. If you continue after 24 hours of curing, you can easily pull the tear-off fabric (peelply) off again.

Step 5. Apply epoxy coating

After the epoxy is fully cured, remove the tear-off fabric and sand the overlaps with 80 grit. Prick open any blisters and seal them with epoxy putty.

You will now apply two layers of epoxy coating. If you wait no longer than 48 hours after the first layer, you can apply the next layer without sanding. Before you begin, clean the entire hull with acetone.

Roll the epoxy coating onto the boat with a velour roller and always wear nitrile gloves.

By applying the epoxy you seal the underlying polyester laminate well and it won't let water through. Your polyester laminate is now 'safe' and osmosis resistant again.

Step 6. Follow-up of the osmosis treatment

After you have carried out the above steps, it is important to apply an anti-fouling coating to the underwater hull. You can do this with a self-sharpening antifouling or a hard antifouling.

Frequently asked questions:

How many square metres is my underwater hull?

Shallow draft boat's hull (powerboat or sailboat):
Area in m2 = 0.5 x length of waterline x (width + draught)                                                                                                                                                                                                                                    

Deep draft boat's hull (sailboat):
Area in m2 = 0.75 x length of waterline x (width + draught)

How does osmosis affect boat strength?

Severe osmosis formation in your boat's laminate can eventually cause delamination. Osmosis can weaken the laminate by separating the different layers. This reduces the strength of the hull. When you treat osmosis on time, you maintain the strength of the boat and treatment is easy.

How do I treat osmosis on my boat?

You can easily treat incipient osmosis yourself. In our step-by-step plan, we describe which products you need and how to proceed.

How do I prevent osmosis on my boat?

Prevention is, of course, better than cure. We therefore recommend regularly having your boat checked for osmosis. Call in an expert and have your boat inspected! Treat your boat with an antifouling layer to prevent osmosis.


Frequently asked questions

How do I calculate the surface area of the underwater hull?

You can calculate the surface area in the following way:

  • Underwater hull for a shallow-draft boat (motorboat or sailing boat):
    Surface area in m2 = 0.5 x length of the waterline x (width + draft)
  • Underwater hull for a deep draft sailing boat:
    Surface area in m2 = 0.75 x length of the waterline x (width + draft)

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Products used in this article

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