| How Osmosis Affects GRP Hulls
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| | on the next.
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| Osmosis is the condition of visible
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| | The one exception to this process is
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| blisters on a boat's hull, caused by
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| | vacuum bagging or resin infusion
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| water absorption.
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| | moulding. This is where dry layers of
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| The process of osmosis is the same
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| | glass cloth and mat are laid in a mould,
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| mechanism by which plants and trees draw
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| | and held in place by either an inflated
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| water up from the soil to their branches
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| | plastic balloon, or another
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| and leaves.
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| | close-matching mould. The resin is then
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| Main Causes of Osmosis.
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| | drawn into the fibres by vacuum suction.
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| Long periods afloat without lay-ups. Warm
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| | The process is more expensive, but is
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| tropical waters. Fresh water is worse
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| | capable of producing very light, strong
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| than salt water. Resins that are coloured
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| | laminates with a high glass content, and
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| (including white ones) are more affected
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| | most importantly, very few air bubbles.
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| than clear resins.
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| | Types of Resin.
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| The Process of Osmosis.
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| | The earliest resins were orthopthalic
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| The fibreglass mouldings on a yacht hull
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| | polyester resins, used in the 1960s. By
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| are not completely waterproof.
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| | around 1980, isopthalic polyester resins
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| Individual water molecules are so small
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| | started to be used as well by some
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| that they can find their way into the
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| | builders, as they were more water
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| layers of glass and resin which form the
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| | resistant. Most builders used these more
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| boat's hull. When molecules of water mix
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| | expensive isopthalic resins only for the
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| with chemicals inside the laminate,
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| | first outer coats, and then saved money
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| problems start to happen. These are
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| | by using the cheaper orthopthalic resins
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| chemicals such as water-soluble
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| | for the inner layers.
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| materials, emulsion binders for example.
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| | Doubling-up on the gelcoat layer is one
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| The water molecules can then have a
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| | method to reduce the risk of osmosis.
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| chemical reaction with these substances,
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| | The latest type of resin, and the most
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| forming larger molecules of a new
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| | expensive, is called vinylester, and is
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| chemical, often acidic. Unlike the
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| | even more waterproof than isopthalic
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| original small water molecules, these
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| | polyester.
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| cannot pass through fibreglass and become
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| | Treatments for Osmosis.
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| trapped. This is the point at which
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| | 1) The best option in most cases is to
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| osmosis starts.
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| | cut or grind open individual blisters,
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| Waterproof Fibreglass Mouldings.
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| | repeatedly wash out with hot water or
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| GRP (glass reinforced plastic), or
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| | steam, to remove the 'blister juice' from
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| fibreglass hulls are comprised of thin
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| | any blisters, dry thoroughly and fill
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| strands of glass. On their own the glass
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| | with epoxy paste.
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| strands are strong but flexible. When
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| | 2) On older boats, if there are no
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| fused with resin it results in a more
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| | blisters, and even if a moisture meter
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| durable substance. Ideally the final
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| | shows high readings, one option is to do
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| moulding should have lots of glass and
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| | nothing! If there are blisters but they
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| only enough resin to hold it together and
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| | are small, they are not likely to have
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| seal in the glass strands, but most
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| | any significant effect on the structural
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| conventional mouldings have much more
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| | strength.
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| resin than this. Generally, the outside
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| | 3) Go to your local 'Osmosis Treatment
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| of a fibreglass hull is coated in a resin
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| | Centre' and have the gelcoat removed, the
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| called a gelcoat. This forms the hard
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| | hull washed and dried out, and the hull
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| outer surface of the hull. Most yacht
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| | recoated with epoxy. This is a costly
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| builders mould the hulls layer by layer,
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| | process and therefore should only be used
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| allowing each layer to set before putting
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| | if all else fails.
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