Plymouth Osmosis Centre


Does your boat suffer from…

  • Blistering on the Hull?
  • The Hull Not drying?
  • Osmosis re-occurrence?

  • HotVac is the innovative patented process and solution for osmosis problems in boats and yachts

    A HotVac treatment can take as little as 10 days for a 10 metre boat - removing the anxiety and frustration of waiting to know if the boat will dry - getting you back on the water quickly, and reducing the likelihood of osmosis re-occurring.

    HotVac can diagnose partial de-lamination and confirm severe hydrolysis breakdown.

    So what are the benefits of using HotVac?
  • Reduce drying time, even with long term "hopeless cases"
  • Remove osmosis and the causes of osmosis
  • Restore structural strength to the hull
  • Post-cure of new hull builds or hull repair work

  • HotVac is the best way to treat osmosis damage.

    What is Osmosis

    Osmosis quite simply is the physical process by which a liquid from a weaker medium is drawn through a semi-permeable membrane into a stronger liquid medium.

    So what does this mean and how does this relate to boat hull damage?

    The simple answer is probably not a lot! Contradicting earlier theories, the damage from “osmosis” is not caused by excessive water permeation. There are absolutely no osmotic forces involved as the gel coat is an absorbing material which can never act as an osmotic membrane! Instead it is the process of hydrolysis, which creates the water soluble corrosive products which in turn create the familiar cavities. (Hydrolysis is the general term given to the reaction of any material with water, for example organic compounds like polyester resin, itself the main constituent of GRP laminates.)

    Once the cavities have formed, then excess water will enter giving rise to high moisture readings. This process may normally be slow, but the presence of free acids or alkalis will greatly accelerate it.

    The first point to note is that it is the phthallic acid, formed in the process of hydrolysis of polyester resin, which causes the chain reaction and subsequent laminate damage, not the water! The acid forms as water insoluble crystals and cannot be washed out of the laminate as claimed by some. Even after years of hard-standing and weekly washes, the acid will remain in the capillaries and cavities, fixed in styrene and glycol. However, water will react with PVA binders in the laminate, reducing them to acetic acid. It is this that gives the strong smell of vinegar when blisters are burst. Even so, it must be noted that the laminate can become severely damaged before any warning blisters appear.

    Osmosis blisters are not only a cosmetic problem. They are the visible sign that the hydrolysis of the polyester has affected at least one laminate layer. By the time the first blister shows, hydrolysed alkali products will have reduced the bond between fibre-glass and polyester deep in the laminate below the water line! This in turn, will have caused a 20-30% loss of structural strength which no “dry and shield” treatment can restore. Without a proper treatment large parts of the laminate layers will sooner or later have larger areas of polyester hydrolysed with only soft wet fibreglass left.

    Studies of hundreds of larger hulls with heavy woven roving mats in the laminate have been undertaken. All were found to have numerous sites inside each roving layer and direct evidence of de-laminations deep in the bulk caused by degrees of severe hydrolysis. Significantly most hulls showed no telltale blisters at all!

    Quality Control is ensured throughout by the equipment we use

    The Gelcoat Peeler

    The removal of the gelcoat is the first stage of the Osmosis blistering treatment and peeling is widely accepted as the most cost effective system for guaranteeing an assured repair.

    The GelPlane offers speed, economy and quality of finish but further and with the dust extraction system the workplace remains clean.

    With our experienced tradesman by using the GelPlane we can control exactly how much gel and laminate is removed so not to compromise the integrity of the hull structure. The hand held GelPlane provides a convenient and controllable method of gelcoat removal.

    The GelPlane will peel as easily on concave curves as on convex and is versatile enough to cut over spray rails around skin fittings and between bilge keels.

    Our experienced operators can peel up to 90 square feet per hour without needing to remove the antifouling first.

    The HotVac Equipment

    Local heating of the treated area is uniform and electronically controlled to within +/- 1°C, thereby preventing hotspots and ensuring complete treatment over the entire area.

    Importantly, microprocessor based timing and temperature control removes all human variability factors.

    The HotVac process combining heat and high vacuum uniquely ensures full removal of all moisture and osmosis inducing chemicals.

    Independent inspections are available at any stage of the process.

    Tramex Moisture Meter

    The moisture meter detects moisture in GRP (Glass Reinforced Plastic) by measuring the resistance between two low frequency AC signals transmitted from the soft rubber electrodes on the base of the instrument.

    Because salt water is more conductive than fresh water, the meter is fitted with different ranges of sensitivity to allow testing of GRP in either fresh or salt water environments.

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