What happens when fiberglass gets wet?
I have heard references to gelcoat being a water proof application for a fiberglass boat hull. I have always considered fiberglass as inherently water proof. There are several industries surrounding fiberglass as a roofing product.
I know gelcoat serves several purposes, most notably it is smooth and UV resistant.
From a boat prospective; The gelcoat is usually applied to the mold, with the fiberglass applied next. To the best of my knowledge no one applies a layer of gelcoat to the inside of the hull. Which means that big fiberglass boat hull is an untreated bucket of water, it is protected on the outside from by the gelcoat, but nothing is protecting the inside. I would imagine in most cases, there is always some standing water someplace in most boats, most drains I have seen leave at least a cup of water in the boat, and I can't say how many I have seen collecting rain water.
What if any damage might soaking fiberglass in water do to the fiberglass?
1 answer
Often when we say "Fibreglass" we're actually referring to a composite of both fibreglass and resin (usually polyester for glass, epoxy for carbon/kevlar - sometimes glass). This is important, that resin is a distinct component was missing from the question.
The composite is formed when glass fabric is shaped in/on a mold and saturated with resin. The resin then cures, forming a rigid structure.
Is this waterproof? Yes. If the resin completely surrounds the fibre.
In production (after initial curing), loose strands will often have to be sanded down and additional resin applied to ensure a compete seal. If, through faulty manufacture or damage, glass is exposed to water (especially salt-water) this will cause to composite to break apart/de-laminate.
So why gelcoat? To protect the glass/resin composite, primarily from UV. Exposing resin to UV will cause it to degrade and crack over time, eventually exposing the fibres to the elements.
Gelcoat has other benefits - it's often more durable and a convenient way of adding a coloured layer. Gelcoat can be applied directly to the mold to form a convenient and better bonded composite, but can also be applied later.
So why doesn't it matter if gelcoat is used on the inside? As above, if the glass is sealed properly with resin, the inside of the boat won't need the extra protection from a gelcoat.
Note: fibreglass roofing should have a clear/colourless gelcoat for UV protection, but of course manufacturers will make whatever they're paid to make.
This post was sourced from https://outdoors.stackexchange.com/a/14207. It is licensed under CC BY-SA 3.0.
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