What to do about missing insulation?
The more I work on my boat the more areas I find where the original fitters have skimped on, or omitted to install, Rockwool insulation; I also find electric cables in the most unlikely places. Short of removing whole panels or cutting out large access panels, which is not practical, I was considering using expanding foam (fire-retardant type) to fill the gaps, if necessary by drilling small holes.
I am, however, concerned about a possible reaction between the foam and the insulation on any hidden cables, or does this only apply to polystyrene foam?
QCans of sprayfoam are usually polyurethane rather than polystyrene and polyurethane is the sprayfoam used on many boats. As far as I know it is only polystyrene that might affect the
Awebsite cable, however, I would make some more points. Rockwool can absorb water and one may well omit it from the hull sides in case it slips down into the bilge. If your gaps are in the cabin sides, the builders might have left a gap between the insulation and window frames so when (and it is when, rather than if) the frame to cabin side seal fails, you have an area for rainwater to leak down into the bilge without saturating any Rockwool.
Take care that you do not create a capillary gap between the foam and insulation or framing. Such small gaps may allow condensation on the metalwork to wick through the gap and stain the trim. If the foam does not make an airtight seal to the metal cabin side, you might get condensation between the foam and metal, causing corrosion.
Be careful about the quantity of foam you inject and try to obtain a zero expansion foam otherwise the lining trim might be forced into bulges as the foam expands.