Re: Permeability to water, was re S&A


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Posted by John Wilson on September 16, 2004 at 00:51:21 from 202.154.157.202 user hugo.

In Reply to: Re: Kon Tiki talk and waterlogged logs, was Re: Swallow and Dreadnought posted by Jonathan Labaree on September 14, 2004 at 14:42:02:

Like (most) Paints, Plastics are not impervious to water vapour. Polythene (actually a trade name for Polyethylene) is used for telephone cable sheathing, but smaller (50-100 pair) telephone cables which once (in New Zealand) were unfilled are now filled with a petroleum jelly to prevent the gaps between the small cable pairs inside the polythene sheath filling with water. Larger cables used in ducts (1-2000 pair say) have a barrier of aluminium foil between layers of polythene to stop the ingress of water vapour - ie the “Barrier Sheathed” cable which replaced the older Lead Sheathed cable.



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