Fridge Vapor Barrier: How to get flat

[scherzoja]

I'm rebuilding my fridge and have question about the vapor barrier.
Does it need to be installed as a single sheet? If so, how to get it to conform to the box shape without having loads of wrinkles and fold-overs?

The rough box is 24" x 40" across the top, one side is the curve of the hull, it's 36" deep. Three sides are 1/2" plywood (aft bulkhead, engine bulkhead, cabinet body) and the floor of the rough box is 1/2" plywood. The hull side also has 1/8" plywood to give a uniform interior surface. I glued (with 3M 90) the Reflectix foil bubble wrap (reflective barrier) onto the plywood, cutting darts and excess away so it conforms to the box shape.

Problem right now is getting the 6 mil plastic sheet vapor barrier to go in without a bunch of wrinkles.

How detrimental to long-term efficacy of vapor barrier's performance would it be to cut darts in the plastic to get it to lie flat against the rough box's interior surface? What is the best tape to tape over the plastic seams? If that's not a good idea, then how do y'all get rid of the wads of plastic that bunches up in the corners?

Attached is a rough diagram of the fridge.

Thanks

[Uncle Bob]

Originally Posted by scherzoja

I'm rebuilding my fridge and have question about the vapor barrier.
Does it need to be installed as a single sheet? If so, how to get it to conform to the box shape without having loads of wrinkles and fold-overs?

The rough box is 24" x 40" across the top, one side is the curve of the hull, it's 36" deep. Three sides are 1/2" plywood (aft bulkhead, engine bulkhead, cabinet body) and the floor of the rough box is 1/2" plywood. The hull side also has 1/8" plywood to give a uniform interior surface. I glued (with 3M 90) the Reflectix foil bubble wrap onto the plywood, cutting darts and excess away so it conforms to the box shape.

Problem right now is getting the 6 mil plastic sheet vapor barrier to go in without a bunch of wrinkles.

How detrimental to long-term efficacy of vapor barrier's performance would it be to cut darts in the plastic to get it to lie flat against the rough box's interior surface? What is the best tape to tape over the plastic seams? If that's not a good idea, then how do y'all get rid of the wads of plastic that bunches up in the corners?

Attached is a rough diagram of the fridge.

Thanks

Someone here at one time suggested using the waterproofing coating used to waterproof bathrooms under tiling. It's water based, brush or roller on and
flexible when cured, accepts tile adhesive without problems and flexible enough to withstand minor movement. If I ever rebuild a fridge that would be my go to.

[wholybee]

Originally Posted by scherzoja

I'm rebuilding my fridge and have question about the vapor barrier.
Does it need to be installed as a single sheet? If so, how to get it to conform to the box shape without having loads of wrinkles and fold-overs?

The rough box is 24" x 40" across the top, one side is the curve of the hull, it's 36" deep. Three sides are 1/2" plywood (aft bulkhead, engine bulkhead, cabinet body) and the floor of the rough box is 1/2" plywood. The hull side also has 1/8" plywood to give a uniform interior surface. I glued (with 3M 90) the Reflectix foil bubble wrap (reflective barrier) onto the plywood, cutting darts and excess away so it conforms to the box shape.

Problem right now is getting the 6 mil plastic sheet vapor barrier to go in without a bunch of wrinkles.

How detrimental to long-term efficacy of vapor barrier's performance would it be to cut darts in the plastic to get it to lie flat against the rough box's interior surface? What is the best tape to tape over the plastic seams? If that's not a good idea, then how do y'all get rid of the wads of plastic that bunches up in the corners?

Attached is a rough diagram of the fridge.

Thanks

I would not cut darts in the vapor barrier to make it fit better. Isn't the plywood a flat piece? I am missing something in your description. Cutting into multiple pieces for each side is fine. I used tyvek brand tape (which is not actually tyvek material) that was next to the Reflectix in the home improvement store. It is just a film tape like packing tape, maybe a bit thicker. It could be used to seal any cuts you made in the reflectix.

What are you going to use for insulation? If you are going to use foam boards, they should be flat as well. Wrinkles in the vapor barrier shouldn't matter at all, but the foam board won't wrinkle.

Pictures of my build are here:
https://www.cruisersforum.com/forums...ml#post3761335

[scherzoja]

Warren,

Yes, the sides are now flat with the 1/8" plywood and I could cut the 6 mil plastic into panel-sized pieces, then tape them in place, but I don't know how long the taped plastic edges will stay taped. If the open up, then the vapor barrier is useless.

The insulation will one or two layers or cyrogel and poly iso for the remaining 3" to 4". I guess I'll just force the 6 mil plastic into shape and maybe soften it a bit with a heat gun to make it as flat as possible, then add one layer of foam board.

Once the top insulation layers are in place (after liner is in), I'll fold the 6 mil over the top and seal around the hatch openings.

[wholybee]

I don't think the tape will come loose. The tape I used was 3 inches wide, so lots of surface contact. Installed correctly, a foam panel will be pressed against the vapor barrier, so there should be no motion or stress on the tape. You don't want there to be any air-space and folds will hold air.

I spent alot (more than healthy) time researching insulation material. Aerogel has a high R value, but is soft and loses insulating properties when it is compressed. It will still have a good R Value, but not what is advertised. It seemed complicated to build some structure to support the box and not compress the aerogel. Polyiso performance is significantly degraded at colder temperatures. R6.5 at 75F, but only R4.5 at 50F, and I couldn't find information on R value at below freezing. I assume less than half of advertised R-Value.

Polyurethane seems to be the best option but I couldn't find it. It seems to have been replaced in construction with Poly-iso, at least in Sunny California. I settled on XPS. I nearly sandwiched VIP panels between XPS sheets, but that would have been too expensive.