Waterproofing Insulation for Fridge/Freezer

[gdavids]

I am in the beginning stages of updating the fridge/freezer on our '86 Hylas 47. I want to make this as efficient as possible, so I'm rebuilding the boxes with all new insulation. After cutting out the inside liner I found that the original foam was very wet, so I'm glad I have gone to this effort.

Hylas did use a good depth of foam around most of the box, but did not really do anything to create a moisture barrier other than lining the hull surface with a thin foil. I want to make sure that the new foam I install stays as nice and dry as possible.

I am thinking of using a combination of polyisocyanurate foam board and spaceloft matt. I realize the polyiso board is not considered to be as moisture resistant as Dow blue board, but it does have a much better R value. My thought is to cut the board to the proper size, glue as many layers together as I can fit, then coat the exterior with epoxy and a sheet of fiberglass to make it totally waterproof. Do any of you have thoughts on this?

The two possible concerns I have is perhaps the epoxy could damage the foam board in some way... or the epoxy and glass could possibly act somewhat as a thermal "bridge" with heat from one side riding around to the other side. Are these concerns worth worrying about?

For dealing with the aerogel spceloft, I am thinking of wrapping it in plastic sheetingthat gets all sealed up. An additional thought is that once the spaceloft blanket is all sealed up, cut a small hole into the plastic. I would then use my wet/dry shop vac to pull out as much air as possible before I quickly tape up the hole. Any thoughts there?

I will also lay down a new foil reflector sheet on the exterior surface of the insulation to reduce radiated heat transfer.

Greg Davids

[Tientos]

Hi Gdavids, we just finished our fridge/freezer rebuild. Details on the blog. Feel free to ask any questions. Cheers


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[Richard Kollmann]

Whether the boat’s icebox has closed or open cell insulation it will not retain its R value over time do to moisture replacing insulating open cell air or out gassing of closed cell gas over time. The simplest way to protect new insulation is to completely encapsulate it in builders 6 to 10 mill plastic then seal all seems with 3M 3350 insulating aluminum tape. This 3M tape is sold by Home Depot and designed to seal HVACR home and industrial ducting.

[gdavids]

Richard,

Do I need to worry about leaving a space between the insulation and outer hull?

While it is a bit more work and expense, what do you think about coating the insulation board with epoxy/glass? My initial sense is that would be even more effective than wrapping the board in plastic. With this technique I would think there should be no air at all in contact with the insulation to cause condensation wetness.

Greg

[steamgoat]

Like this guy did ?Marine refrigeration and freezer on 22 AH per day

[gdavids]

Yes, exactly like he did. I find the level of detail in his job almost overwhelming, but I am very interested in that idea of sealing the foam. The one thing I am unsure of is if thermal bridging could be a "thing"? The foam board is great for isolating heat, but I don't think epoxy and glass are particularly good in that regard. I am wondering if anyone here has knowledge about if this is a realistic concern.

[Hard Rock Candy]

I'm back. Air against the foam inside a plastic bag will not generate any moisture. If the foam has no air flow across it it will not get Condensation on it. The condensation is the humidity in the air that is normally circulating through the boat. No new air, no new water. I may have lost it here but do not try to vacuum the air out. Normal sea level atmospheric pressure is approximately 15 lbs per square inch. so if the area of foam that you have inclose in an airtight bag is 1 ft square and you have drawn a 2 lb. vacuum, You have about 188 lbs, Per square foot of pressure against the foam on all sides, so it will over time collapse the foam to some extent. Mac

[Terra Nova]

Originally Posted by gdavids

...once the spaceloft blanket is all sealed up, cut a small hole into the plastic. I would then use my wet/dry shop vac to pull out as much air as possible before I quickly tape up the hole. Any thoughts there?...

Thanks for the humor.

Your wet foam is due to no vapor barrier and the wrong foam. Don't forget an infrared barrier as well. I wouldn't bother experimenting with high tech solutions and homespun remedies.

[zboss]

I've been doing research on polyisocyanurate myself for this very reason. The new generation of polyiso is much more resistant to water than the old stuff, basically retaining most of the R value over 15 years. They do recommend wrapping with something more along the lines of Tyvek rather than just regular plastic sheeting to allow moisture to evaporate, without allowing too much in.

I'd still seal it. We are going to put in a box, glass it, use a radiant barrier, and use 4 inches of iso which should give us an r value of about 25. Then we will line with fiberglass.

[gdavids]

That is an interesting idea using Tyvek as a wrap instead of regular plastic. Any thoughts on this Richard Kollmann? The timing for this info is very good, as I am right at the stage of dealing with new insulation.

[SV THIRD DAY]

We recommend the plastic approach to our clients over Tyvek. It's air movement that kills you with condensation and plastic will 100% stop it.

But lets not forget the Foil tape on all the cut edges and corner of the PolyIso!

[zboss]

This was an interesting read...

Basically it says that polyiso performs worse as the outside temperature goes down and goes up the hotter it gets outside, not linearly though. It makes the recommendation to use "thicker" polyiso, which I take to mean that each sheet is thicker... so instead of using four sheets of 1", use 1 sheet of 4".

It also pointed out that there were pretty large differences in the R Value between manufacturers.



Temperature Depend. of R-values in PIR Roof Insulation | BSC

[SV THIRD DAY]

Originally Posted by zboss

This was an interesting read...

Basically it says that polyiso performs worse as the outside temperature goes down and goes up the hotter it gets outside, not linearly though. It makes the recommendation to use "thicker" polyiso, which I take to mean that each sheet is thicker... so instead of using four sheets of 1", use 1 sheet of 4".

It also pointed out that there were pretty large differences in the R Value between manufacturers.



Temperature Depend. of R-values in PIR Roof Insulation | BSC

Like the Hotter temps in the Tropics.......

Actually stacking 1" sheets of foil lined PolyIso is just as good a using a 4" sheet....at least that's what our test data shows. Plus it is MUCH easier to work with the 1".

[Terra Nova]

When using multiple sheets, be careful of creating air gaps, which must be avoided.

[hellosailor]

Greg-
There are also a number of roofing materials that are waterproof membranes, similar to a rubber or silicone sheet that is either heat-sealed on seams, or self-adhesive backed. I'm sure a whole roll at the local home/roofing supply would be way more than you need, but if there's some local construction or a job site where you could pick up a few yards, it might be cheaper and certainly less fuss than epoxy and fiberglass. And certainly as durable.