How do you treat osmosis on your boat?

© Osmose Services

Osmosis is a phenomenon that affects older polyester sailboats left in the water constantly. Recognizable by the formation of blisters on the hull, it is certainly irreversible, but can be treated.

Preventing osmosis

To avoid osmosis, there is no need for preventive treatment, even if it exists. This involves applying a solvent-free water-based epoxy resin to the gel-coat, which will seal your boat. But this process is quite expensive.

Instead, opt to reduce the time your boat is in the water. For example, give preference to winterization. By keeping your boat dry during the off-season, you will allow the water accumulated in the hull to evaporate.

And if osmosis has set in, what traitement??

To prevent delamination of the hull of your boat, it must undergo an anti-osmosis treatment. This is a multi-step process and must be carried out by a professional.

Step 1

First of all, the hull of the boat must be exposed. To do this, the gel-coat must be peeled until the polyester fibres appear using an electric planer, or the technique of sandblasting or hydro-spraying.

Coque mise à nue
Bare hull

Step 2

The hull must then be allowed to air dry. Count between 3 and 6 months in winter and about 3 months in summer. To speed up the process, you can install your boat in a dry, heated place and use a dehumidifier. To control hull moisture, use a tester.

Step 3

Next, we need to cover the hull with an epoxy product solvent-free to avoid the formation of bubbles favourable to osmosis. Choose a closed area with low humidity. It will be necessary to take care to respect the temperatures and the drying times, it is for this reason that entrusting this mission to a professional is more judicious.

Pose d'un primaire epoxy
Installation of an epoxy primer

It is necessary to count between 3 or 3 coats applied with the roller to cover the hull of your boat.

Step 4

The last step is to apply an antifouling. First the epoxy layer will have to be sanded down, then a primer and finally the antifouling will have to be applied.

Nettoyage de coque avec la pose d'antifouling
Hull cleaning with antifouling installation

Which tarif??

Before taking any steps, ask for an estimate to evaluate the viability and relevance of the curative treatment. Indeed some boats are old and their value is very low. This will be all the more important if you buy a used osmosis boat.

It costs about 400 euros per square metre of hull area.

How long does an antiosmose? treatment last?

After about 3 weeks of curative treatment (without the drying time), your boat will be able to regain water. You normally do not need to redo this treatment, but it is possible that some areas may not have been able to receive a complete treatment.

Is it possible to buy a boat osmosé??

Yes, but we'll have to call in an expert to assess the osmosis state of the hull. It will also be necessary to integrate the costs of the treatment in the purchase price and thus negotiate with the seller.

If you choose to buy an osmosis boat, prefer a boat that hasn't had a curative treatment yet, or one that has been professionally built.

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