Steel Hull Insulation

[Pauls]

Micah, I assume that you are doing new construction, or are rebuilding from a bare hull. That being the case, there is plenty of real world experience that you will not have a problem with corrosion under the sprayed in closed cell foam, if you do proper prep first. Points on this:
1. A properly done paint job on steel, meaning blast to near white metal, test for salts on the steel after blasting, if needed use the Chlor-Rid (I've used it, it works very well), then inorganic zinc, then several coats of a good epoxy.
2. A high quality paint job like this is generally considered good for 30 years. And think about it - this paint is on the hull interior and it is under a couple inches of closed cell foam. This is the best protected paint job in the world. It will not be exposed to any UV. It cannot be banged and damaged, the foam protects it.
3. The foam is only sprayed above the cabin sole.
4. Many boats have been insulated this way. There is a good consensus that this is the best technique.
5. If you try to fit foam blocks and then install a vapor barrier it is virtually guaranteed that the vapor barrier will leak somewhere, with the result that you will have condensation. Which is lousy for the interior environment, and is harder on your interior paint than keeping it dry and sealed behind the foam.

Do a good job with the interior paint, spray in the foam, and you will not need to inspect the interior for rust. It will outlast you.

[micah719]

Originally Posted by Pauls

Micah, I assume that you are doing new construction, or are rebuilding from a bare hull. That being the case, there is plenty of real world experience that you will not have a problem with corrosion under the sprayed in closed cell foam, if you do proper prep first. Points on this:
1. A properly done paint job on steel, meaning blast to near white metal, test for salts on the steel after blasting, if needed use the Chlor-Rid (I've used it, it works very well), then inorganic zinc, then several coats of a good epoxy.
2. A high quality paint job like this is generally considered good for 30 years. And think about it - this paint is on the hull interior and it is under a couple inches of closed cell foam. This is the best protected paint job in the world. It will not be exposed to any UV. It cannot be banged and damaged, the foam protects it.
3. The foam is only sprayed above the cabin sole.
4. Many boats have been insulated this way. There is a good consensus that this is the best technique.
5. If you try to fit foam blocks and then install a vapor barrier it is virtually guaranteed that the vapor barrier will leak somewhere, with the result that you will have condensation. Which is lousy for the interior environment, and is harder on your interior paint than keeping it dry and sealed behind the foam.

Do a good job with the interior paint, spray in the foam, and you will not need to inspect the interior for rust. It will outlast you.

Yes, you're steering me closer to a sensible solution. Of course, I could have both.....removable insulation in places where it makes sense, and fixed permanent insulation for the greatest part where I have no good reason to mess with.....providing I get the prep and initial seal absolutely correct.

And yes, it's a new build, something I should amend in my CF bio-blurb...

[Sailormantx]

As others have said, proper painting is key to protecting steel under the insulation. Foam is for insulation, not protection of the steel and should never be applied over uncoated steel. Using closed cell foam, it adheres to the metal tightly and there will be no condensation behind it because the interior air cannot touch the metal. I use a product from Tiger Foam that is also fire retardant. I have welded close by it many times with no fire or fume problems when welding spatter gets on it - I scrape it away several inches around the weld site.Tiger Foam | Spray Foam Insulation Kit | TF-600FR