Reefer box construction - vapor barrier?

[jordanbigel]

Sorry to ask more dumb questions, but...

We've ripped out the old freezer and reefer boxes, and now we have a big empty hole lined with marine plywood (see below).

My plan is to lay down layers of insulation (Polyiso and XPS next to the box) working my way in from the sides till I have the right shape of the box, then assemble in place panels of FRP (thinking of using 1/4" FRP panels from rParts for this purpose) and epoxy them together, filleting the inside seams, etc.

The main question I have now is what do I line the outside of the hole with before I lay down the first layer of insulation?

The second question is what is the best way to glue them together - some say 3M 77 others say contact cement. What is best?

Also, I've read some people saying they coat all the insulation with some kind of silicone or epoxy to seal it? What is this about and is it necessary for the polyiso?

Really need guidance here, I am at the stage where I need to start laying down insulation, and I feel like I am blocked by these questions. Please help!

Thanks!

[goboatingnow]

I would only use close cell insulation anyway , so no chance of water ingress

[jordanbigel]

Originally Posted by goboatingnow

I would only use close cell insulation anyway , so no chance of water ingress

Based on what I have learned to date, both Polyisocynurate and XPS (Extruded Polystyrene) are closed cell foams, but that water will condense on them, between the boards, and diminish r-factor over time. I think its much worse with the Polyiso, but I am not certain exactly why.

I just think it is a bit more complicated than "use closed cell foam". I could be wrong of course, I have never done this before.

[Bellinghamster]

I did similar when I improved my refer box, except it was an already insulated fiberglass box that I built up more insulation (3" of foil faced polyiso), then installed a new fiberglass liner made from fiberglass shower panels from Home Depot (textured one one side, smooth on the other, flexible enough to fit the curve of the hull yet plenty rigid for a box liner, available I
4x8 sheets surprisingly cheap). i filleted the imside corners with thickened epoxy then painted the interior with polyurethane. I should have used a catalyzed urethane or epoxy paint as it took a long time to harden. I'd I were starting with a plywood box, I'd epoxy coat it inside and out, then build the same way.

[jordanbigel]

For the box itself I plan to use 1/4" FRP panels from rParts.com.

I'm also going to use a food grade white epoxy paint on the inside based on other threads I've read about that. (This stuff: https://www.epoxyusa.com/ProductDeta...=EP34&CartID=1)

Did you treat the Polyiso with anything - I've read several threads on CF where someone says they either epoxy coated the foam, or used a silicone sealer?

[Bellinghamster]

The polyiso foam I used was foil faced both sides and I taped the exposed edges with 2" foil tape so they were completely sealed panels. Staggered overlaps in the corners and filled any gaps with expanding foam (from a can, i.e great stuff if equivalent)

[bdgWesternMass]

Originally Posted by jordanbigel

For the box itself I plan to use 1/4" FRP panels from rParts.com.

I'm also going to use a food grade white epoxy paint on the inside based on other threads I've read about that. (This stuff: https://www.epoxyusa.com/ProductDeta...=EP34&CartID=1)

Did you treat the Polyiso with anything - I've read several threads on CF where someone says they either epoxy coated the foam, or used a silicone sealer?

3m 77 can be done without coating it.

I would use a latex paint coating for contact cement. I believe the contact cement will eat the foam, spray paint will also.

I think coating the bare,foam is good.

[mvweebles]

For barrier, you could use Tyvek house wrap. There are a few sellers on Amazon selling as ground clothes in smaller sizes than 150-foot rolls (HERE is an example). The tape is also useable - Dupont product claims to be waterproof. I doubt there is a better, more ecomonical choice.

1/4" fiberglass is way overkill. I'm assuing you chose that so you could edge-glue, which is also not necessary. 1/8" is very strong and workable. McMaster Carr also sells fiberglass sheets in 1/32" increments. Appears to be slightly less expensive than the rparts version. The surface is very smooth and ready for primer/paint (will need a light scuffing with 220-grit).

https://www.mcmaster.com/sheets/grade~gpo3/

[ItDepends]

There are a lot of people who take bits and pieces of good advice, and make a mash of it because they don’t really understand what’s important. There are four critical features of a high performance, long lasting cold box.

1. As much insulation as practical. For a cold freezer, you start to get into reducing returns when you get to 6” thick of any of the foams. 4” should be considered a bare minimum.

2. Keep water vapor 100% OUT of the insulation. This kills most boxes. Closed cell foam is nice, but it WILL absorb water over time and this will kill its performance. Epoxy coat the wood with multiple coats, seal the insulation space with plastic sheet, every thing you can think of to keep it air tight.

3. Make sure there in NO space inside the insulation space for air to move around. Every gap or crack needs to be filled or the moving air will transport heat. Doesn’t really matter what you fill with, silicone, spray foam, 5200. Whatever. Just NO free air space.

4. A superior gasket seal. A good double seal, properly designed and implemented is critical.

[mvweebles]

Originally Posted by ItDepends

]
1. As much insulation as practical. For a cold freezer, you start to get into reducing returns when you get to 6” thick of any of the foams. 4” should be considered a bare minimum.

I wish 6" was practical. Household counters are 24-inches deep. Boats are often a few inches less. If the cavity is 24Dx36Wx30H, you would end up with a fridge with dimensions of 12x24x18, not much larger than a large milk crate.

This type of guidance comes from the old days of flood acid batteries and very limited power generator options. Another strategy would be accept some inefficiency in exchange for carrying capacity - upsize the refrigeration unit, and add an extra solar panel and LiFePO4 battery.

[jordanbigel]

Originally Posted by mvweebles

For barrier, you could use Tyvek house wrap. There are a few sellers on Amazon selling as ground clothes in smaller sizes than 150-foot rolls (HERE is an example). The tape is also useable - Dupont product claims to be waterproof. I doubt there is a better, more ecomonical choice.

1/4" fiberglass is way overkill. I'm assuing you chose that so you could edge-glue, which is also not necessary. 1/8" is very strong and workable. McMaster Carr also sells fiberglass sheets in 1/32" increments. Appears to be slightly less expensive than the rparts version. The surface is very smooth and ready for primer/paint (will need a light scuffing with 220-grit).

https://www.mcmaster.com/sheets/grade~gpo3/

Thanks. A friend suggested Tyvek, he has a spare roll.

The reason I chose the 1/4" FRP is to mount holding plates - not evaporators. They weight about 30lbs each. I'm thinking it will ensure secure mounting for the plates.

[rbk]

Originally Posted by jordanbigel

Thanks. A friend suggested Tyvek, he has a spare roll.

The reason I chose the 1/4" FRP is to mount holding plates - not evaporators. They weight about 30lbs each. I'm thinking it will ensure secure mounting for the plates.

Tyvek is not a vapour barrier and is specifically designed to be vapour permeable. Polyiso’s R value degrades as temperatures drop and as time goes by due to the blowing agent used in the foam; foil faced polyiso is considered a good vapour barrier if the seams are properly taped/sealed but the stated R value takes into consideration the reflective properties of the foil which in order to work requires a minimum 1” air space and would best be placed on the exterior of the freezer box and where the vapour barrier should be (warm side). If it were me 1” foil faced polyiso, then 2-4” of hs40 (strong, high compression and performance increases with colder temps) 1/8” RFP epoxy layup and final coat of good grade paint, gel coat or whatever your comfortable with. Don’t forget a drain and plug in the bottom. The epoxy and finish should ensure a watertight seal from the interior and even if the hs40 were to wet it does not hold water. Other option would be make make mold for fridge space and spray 2 part ccspf in the entire void in small lifts then finish interior.

[s/v Jedi]

I started with aluminum foil, shiny side out, glued with spray glue. This is the radiation barrier. I coated that with epoxy for the vapor barrier, then used the blue refrigeration foam (think that was Dupont). For the inner liner I used 3/4” plywood covered with fiberglass.

Lots of pictures here: https://sv-jedi.smugmug.com/Projects...Refrigeration/

[mvweebles]

Originally Posted by jordanbigel

Thanks. A friend suggested Tyvek, he has a spare roll.



The reason I chose the 1/4" FRP is to mount holding plates - not evaporators. They weight about 30lbs each. I'm thinking it will ensure secure mounting for the plates.

From the picture, looks like you may need to curve along the hull. 1/4" will be too stiff. You can double or trople the thickness of 1/8" at mounting points.

Tyvek is indeed vapor permeable. It's designed that way to prevent moisture from becoming trapped and saturating insulation,

https://www.dupont.com/knowledge/top...ier-myths.html

But if you dont trust dupont tyvek to be the right material and you want a 100% impermeable surface, consider liquid membrane used for tiling showers. It's thick and would work fine as an adhesive for your FRP panels. Cheaper, easier, faster, and better than epoxy because it is slightly elastic.

Very few custom fridges are made nowadays. There are better materials available now that are better and easier to work with compared to fiberglass over plywood layup with gelcoat and a ton of sanding.

[jordanbigel]

Originally Posted by mvweebles

From the picture, looks like you may need to curve along the hull. 1/4" will be too stiff. You can double or trople the thickness of 1/8" at mounting points.

Tyvek is indeed vapor permeable. It's designed that way to prevent moisture from becoming trapped and saturating insulation,

https://www.dupont.com/knowledge/top...ier-myths.html

But if you dont trust dupont tyvek to be the right material and you want a 100% impermeable surface, consider liquid membrane used for tiling showers. It's thick and would work fine as an adhesive for your FRP panels. Cheaper, easier, faster, and better than epoxy because it is slightly elastic.

Very few custom fridges are made nowadays. There are better materials available now that are better and easier to work with compared to fiberglass over plywood layup with gelcoat and a ton of sanding.

The thing is that there seem to be 2 opposing viewpoints - some people think the secret sauce is absolute air-tight seal of the insulation (which I am still not clear on how to achieve) and others suggest, as you do, that you want it to breathe.

I think there is logic to the first viewpoint - if no air gets in, no water can get in.

And, the Dupont article "weather barrier myths" is about insulating a house, not a freezer box. I am not sure the issues are the same, in fact, I'm certain they are not the same, but I still don't know which camp is right.

I have read several other threads (man, I have read a lot of threads on this topic) where some people have repeated this idea that they have to breathe, and others, again, suggesting the secret is to make it air-tight. I even read one thread (from like 2005?) where a guy said he sealed up all the insulation air tight, then a few days later he read that it has to breather or it will trap moisture, so he spent a day removing the sealing on one side or something like that. Sigh.