This is a post on my views and experiences with insulation on board Lady Jane.
I have written this in response to the questions/comments I've had recently on the subject and, hopefully, as a means of helping others. I apologise if it's a little long. This piece was originally longer, but I chopped it already.
I don't claim to be an expert in any of this, having only the experience of Lady Jane as the basis for this piece. There are, I'm sure, people better qualified than me to comment, but ultimately it's really only time that will tell which approach is the best.
Oh yes, and I can only really speak of insulating a steel boat, though obviously some of this will apply to other types of vessel as well.
First off, steel and water do not get on, especially steel and salty water. The issue with salt water is that once it evaporates, the salt remains. This salt then gets damp when the humidity goes up, making the steel wet again without even adding visible moisture - hence salty water causes rust issues for cars from coastal places.
It seems to me that steel and water get along least well when the water is trapped against the steel in an evaporate/soak type cycle.
The worst scenario seems to be damp wood against steel
- especially if the damp has a high salt content and more salt gets added over time. It also seems to me that painted steel which has then rusted tends to get worse faster than rusty untreated steel.
Now everybody knows that when warm air hits a cold surface, the moisture in the air condenses out - great for a cool mental image of a cold beer on a warm day, bad for standing in the galley cooking breakfast with condensation raining down your neck
Ok, so in terms of insulation on a steel boat, the basic trick is to ensure that water, in any form, does not get trapped against the steel.
If warm air inside is prevented from getting to any steel cooled from outside, condensation and therefore the ensuing dampness and ultimately rusting should not occur. Though in reality, to some extent, moisture will inevitably get through regardless of how much effort has gone into providing a good moisture barrier.
I believe that, no matter what insulation is chosen, the basis for preventing rust issues behind insulation is primarily good preparation of the underlying surfaces. A really good cleanup of the steel, followed by at least three coats of good quality primer being the minimum. That way, any moisture sits against paint, and not steel.
The deck head in both the galley
and in the wheelhouse on Lady Jane was insulated with expanded foam and covered over with cheap chipboard with a thin plastic laminate layer on the outside. Some forty years later, when I removed the insulation, the underlying, painted, steel was still mostly in good condition even though it was obvious the expanded foam had been damp and, inevitably, some rust had occurred.
Admittedly there were holes in both the wheelhouse and galley deck heads, but the holes seem most likely to have been caused by rusting from above, rather than from inside. Once moisture had got in behind the insulation, the resulting rust was not a pretty sight, but that's a different issue.
Down below, bitumen had been used to protect the steel. Much of the steel was like brand new forty years later - even down to the original craftsmen's chalk marks which were still visible.
Because of all the above, so far as I'm concerned, the best insulation to use is dependant more on it's effectiveness, practicality in applying it and, of course, the money you have available to you.
Ideally, I suppose, the steel behind any insulation should be 'serviced' every say 10 years, to monitor and stay on top of any potential rust issues. Thinking through some of what I've done, this is not really practical though.
The best insulation, by a long way, that I have come across has been two part polyurethane expanding foam insulation
when it has been properly applied. The foam is sprayed onto the prepared surface in a very similar manner to spray painting. Obviously the steel surface must be well prepared and painted, so the spray foam can adhere to the surface. Applying the spray foam takes some preparation, but is fast and very efficient. We are talking hours versus days compared with some of the other stuff I've used. I also believe the spray foam does away with any issues of water getting behind the insulation, as the spray foam is effectively an extension of the coating given to the steel.
The next best insulation I've found has been the likes of Kingspan or Xtratherm
- shown above, which is a similar material to the spray foam. There are plenty of different trade names for this. You simply buy huge sheets of the stuff at whichever thickness suits you. The cutting and fitting the insulation sheeting is messy and time consuming though. In comparison to the spray foam, I'd say it's difficult to fill all those difficult little spaces that the spray foam just blasts into and fills in no time. I found filling the gaps with the two part polyurethane spray foam worked will though.
I have also been using the hi-tech insulation foil
. - shown above, which does seem to insulate remarkably well given it's thickness. This stuff I have simply been cutting to shape and gluing in place with cheap glue. I figure it's so thin and light that even flour and water would probably keep it in place (not that I've tried).
This high-tech insulation has proved great for places where it's just not practical to put in thicker insulation, such as on some of the walls of the galley and in the space above the engine room.
I have found it fun to test the effectiveness of what I've done by using a cheap infra-red thermometer to gage the effectiveness of the insulation I've installed. Reading -2C on the steel outside and 18C on the insulation inside makes me feel pretty good about things.
The thing I'm finding on Lady Jane is that some insulation, any insulation, is so much better than nothing. The more the better, up to a point obviously.
Thinking of the bare steel as a kind of reverse radiator, anything to prevent the contact of warm air against that steel will minimise condensation and prevent the steel from absorbing the heat from the air it would otherwise be in contact with.
One last word. I'm planning on gluing plywood panelling straight onto the insulation and, where practical, augmenting this glue with wooden battens to help hold the whole lot in place. Again, any old glue will do as the ply is thin and light. The ply will be painted over, so there should be no issues with the ply de-laminating. There is already similar ply elsewhere on board, and there has been no de-laminating issues.
I hope this helps. Feel free to add your comments if you have anything constructive to add to this for others.