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Q & A

Foil insulation.

Can foil insulation be bonded to GRP cabin sides with Automotive grade carpet trim over the foil to finish. If so, what is the recommended adhesive?

Asked by: chris king  | 7.38am, Saturday 25 February

WW says:

I would suggest trying rubber solution contact adhesive to stick the insulation to the GRP. As far as sticking the carpet to the foil, carpet layers use a spray glue, which might be a different version of contact adhesive thinking about it!
I think this will stand up to the rigours of a potentially damp environment, but will need careful planning and application. It is a good idea and do please let us know how you get on and how successful it is as there are lots of GRP cruisers out there with similar problems.

Rupert Smedley  | 9.13AM, Saturday 25 February

In my old cruiser, we bonded foam backed carpet directly to the GRP, on both the hullside and cabin roof. Adding two extra roof vents as well to ensure good airflow eliminated condensation the cabin and hull sides.
I do wonder if foil insulation would have much effect, as thin foil would only reflect radiated heat, rather than via directly conduction (thermal transfer) which is where most heat loss will occur. However, as long as you can make it stick well (and the carpet stick to the foil) then nothing to lose.
Incidentally, adding lining to curtains we found (on a Norman Conquest and a Norman 23) dramatically increased the temperature stability!

Mark Langley  | 5.27PM, Saturday 25 February

I agree with Rupert's and Mark's comments, in particular that foil insulation will only reflect radiated heat. It is not a substitute for other forms of insulation like foam or Thinsulate which trap air and reduce heat loss from conduction. Also, to work properly, at least one surface of the foil should face an air space.
The other benefit of foil insulation is that it can act as a moisture vapour barrier but it needs to be on the 'warm' side of the other insulation to enable it to do this.
Warm, moisture laden air in the cabin will pass through the insulated sides until the temperature drops to the 'dew point'. When this happens. the moisture in the air turns into condensation. If the temperature of the moisture in the air can be kept above the dew point, no condensation will occur. One way to achieve this is to place a moisture vapour barrier in the path of the moist air so that it stays above the dew point.
The problem with doing as you suggest is that you could find that, in extreme conditions, the carpet has condensation on the surface or, possibly worse still, that the condensation forms within the carpet or on the backing.
The only real solution is to apply a good layer of insulation followed by a vapour barrier (if the insulation is not inherently moisture resistant) but, as you say, this is probably not practical. I would try using a carpet that is not likely to rot too easily and keep an eye on it for any sign of dampness.

Graham Booth  | 11.54AM, Sunday 26 February

Readers say:

Thanks WW. We are thinking on the same lines.
I don't see how it couldn't be beneficial, re: condensation as well as heat transference. I know in the building trade they are designed to be used to contain airspace for max. efficency, equivalent to 50mm poly-foam. Anything is better than nothing and you cant go sticking 50mm poly-foam inside a 2 berth.
Unless you want to make it a 1 berth.

chris king  | 3.07PM, Saturday 25 February

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