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I am told fibreglass boats deteriorate over time. What is the bast means of preserving?

Asked by: g. williams  | 11.08am, Tuesday 2 August

WW says:

Apart from damage to the hull surface from contact with locks and hard banks, the major problem that GRP boats suffer from is osmosis. Constant water pressure can cause moisture penetration of the hull on a microscopic scale. However, this is sufficient to raise blisters of gas by chemical reaction with improperly cured constituents of the glass-fibre. Many canal craft were moulded in unsophisticated conditions which increases their vulnerability.
Taking steps to pre-empt osmosis can be cost-effective as it may increase a craft's value by more than the cost of materials involved. International's Gel-Shield, an epoxy resin coating that is impermeable to water, is a well-known treatment. If osmosis is caught at a very early stage - where pimples are barely discernible - coating can take place after the hull has been thoroughly dried out by lying up ashore over winter (moisture content should not exceed 5%).
If osmosis is more advanced - forming larger blisters - the glass-fibre surface must be taken off until all blisters are destroyed. This can be done by abrasive blasting or in specialist treatment centres using gel-coat peeling machines. After the exposed surface has dried out during prolonged lay-up ashore or under special heat lamps, a thicker coating of Gel-shield - three coats instead of two - is applied, or five coats of epoxy paint.
Once the hull is treated, the underwater part can be painted with an environmentally acceptable antifouling. This should be taken six to eight inches above the waterline. Antifouling should provide additional protection for the surface of the gel coat and, hopefully, prolong its life.

Graham Booth  | 12.07PM, Tuesday 2 August

Keeping the bilge dry is also important. It is possible to detect the present of alkaline compounds in the interior of the fibreglass (using red litmus paper, for example). Much of the osmostic blistering occurs from within the glassfibre and from the air, not just through the external, water-facing gelcoat. This means that checking the bilge to ensure it is dry- and ventilated- is important- and checking any water to see if it has a very high or low pH.
However, unless the osmotic blistering is highly advanced and is threatening the integrity of the hull, it can often be ignored, given to overall value of the boat. Laying up ashore for a few months a year can also reduce the presence of water- using Gel-Shield requires rather precise application in controlled conditions, otherwise you may inadvertently trap more moisture within the composite matrix.
Antifouling may not always be the best cooating, as most are permeable to a degree- especially the eroding types. An alternative would be an epoxy based copper coat, which further seals the gelcoat, and also acts as a antifouling for 10 years plus. In the long term, it may be more cost effective.

Mark Langley  | 1.00PM, Tuesday 2 August

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