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Posted: Sat Dec 05, 2015 12:15am

Post Subject: Hull Insulation (or lack off)

Hi The more I work on my boat the more areas I find where the original fitters have skimped on, or rather omitted to install, rock wool insulation, I also find electric cables in the most unlikely places as well. Short of removing whole cladding panels or cutting out large access panels, which is not practical, I was considering using expanding foam (fire retarded type) to fill the gaps, if necessary by drilling small holes through which to inject it. I am however concerned about possible reaction (leaching of the plasticisers from the cable's insulation) between the foam and any electric cables that may be hidden or does this only apply to polystyrene foam? As any enclosure of cables in expanded foam is only likely to be a very short length I am not concerned with de-rating of the cables. Your thoughts on this would be much appreciated. Thanks P Caswell


Posted: Sat Dec 05, 2015 9:57am

Post Subject: Hull Insulation (or lack off)

Cans of spray foam are usually polyurethane rather than polystyrene and polyurethane is the "spray foam" used on many bots. As far as I know it is only polystyrene that may affect the cable. However I would make some more points. You use the term hull in the title rather than cabin side and with rockwool that can absorb and wick water one may well omit it from the actual hull sides in case it slips down into the bilge where it may make contact with water so it all becomes wet. If it is the hull sides (rather than cabin sides) I am not sure I would try to fill in any gaps. You may also find that the builders have left a gap between the insulation and window frames so when (and it is when, rather that if) the frame to cabin side seal fails you have an area fro rain water to leak down into the bilge rather than saturate the rockwool. You will also need to take care that you do not create a capillary gap between the foam and insulation or internal framing. If you do condensation on the hull may wick through the gap and stain the cabin side trim from the back. Be very careful about the quantity of foam you inject and try to obtain a zero expansion foam, otherwise I could see the lining trim being forced into bulges as the foam expands. If the foam does not make and airtight seal to the metal cabin side you may get condensation trapped between the foam and the metal thus leading to corrosion. There is a fair bit to think about and to weight up the pros and cons of doing what you suggest but the foam should not affect the cable insulation.

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