Epoxy over two part polyurethane foam

[GILow]

Hi all,

Does anyone have any tips for glassing over two part polyurethane foam with epoxy?

I have faired the inside of my new hull-integrated water tanks using two part foam and I am planning to do the internal fibreglass layer tomorrow. Looking at it all, I suddenly wondered if I might run into problems with the two materials.

Matt

[coopec43]

Matt

I don't think you'll have a problem. I plan to join two slabs of polyurethane foam insulation on my fridge/freezer with epoxy.

Cheers

Clive

[Chotu]

Matt: You are fine. Epoxy is compatible with that foam. Laminate away.

Clive: you can use anything equal or greater in strength to the foam to bond your core together. No need for epoxy.

Gorilla glue, any polyurethane glue.

[coopec43]

Originally Posted by Chotu

Matt: You are fine. Epoxy is compatible with that foam. Laminate away.

Clive: you can use anything equal or greater in strength to the foam to bond your core together. No need for epoxy.

Gorilla glue, any polyurethane glue.

Thanks for that but it is not a matter of strength. When water is absorbed by polyurethane foam it loses it's insulation properties. (I am using epoxy as a moisture barrier)

I am using rigid slabs of polyurethane foam which is one of the best but it does absorb water. The best reference I can find right now is:

Therefore, expanded polyurethane foams are widely used as insulation in fish holds/fish containers together with a lining of fibreglassreinforced plastic, despite the fact that they are significantly more expensive than expanded polystyrene. Their main technical limitation is the fact that they are more likely to absorb water than expanded polystyrene, an......

5. Thermal insulation materials, technical characteristics and selection criteria

[GILow]

Originally Posted by Chotu

Matt: You are fine. Epoxy is compatible with that foam. Laminate away.

Good to know, thank you.

[Spot]

In the surfboard world, it is generally accepted that polyurethane foams absorb less moisture than lighter weight expanded polystyrene foams due to the structures of the foams. Air and water move more freely through lightweight EPS than PU foams. Larger boards like stand-up paddle boards made from lightweight EPS need air vents or else they expand and de-laminate when exposed to higher temperatures. Surfboard PU foam is around 2-3 PCF (pounds per cubic foot), EPS 1-2PCF. The EPS from the big box stores is usually a 'short' .88 PCF and is not as pleasant to work with compared to heavier EPS. My boards are from 1.5 PCF EPS.

The combination of polyurethane foam and glass cloth and epoxy resin is considered by some to be a righteous build as the foam blanks are cheaper/easier to find and shape and the resin is free of solvents and has better mechanical properties, and the dings absorb less water. The downside is the cost of the epoxy resin and whatever quirks that epoxy brand has for blushing or UV stability. There is also trouble for some when laminating in cooler temperatures as the epoxy is not made with solvents like polyester resin so it does not 'flow' or 'waterfall' like polyester. Warming the room, warming the resin, adding small amounts of solvents, and changing work methods are typical workarounds.

In my own experience with wood and epoxy builds, the downfalls comes from a lack of cloth over the wood allowing exposure and movement leading to cracks and pinholes when laminating cloth. When I built the dinghy I did cloth on the bottom which is doing well after 3 years sitting outside freeze, thaw, bake...but the areas where I just coated the plywood with epoxy look worse for wear. The areas not exposed to sunlight look better. If I had it to do over it'd be cloth over everything exposed to weather and something over the epoxy (varnish, LPU) to help with pinholes and UV.

I guess UV should not be an issue in the tanks, pinholes would see moisture all the time...

[Chotu]

Originally Posted by coopec43

Thanks for that but it is not a matter of strength. When water is absorbed by polyurethane foam it loses it's insulation properties. (I am using epoxy as a moisture barrier)

I am using rigid slabs of polyurethane foam which is one of the best but it does absorb water. The best reference I can find right now is:

Therefore, expanded polyurethane foams are widely used as insulation in fish holds/fish containers together with a lining of fibreglassreinforced plastic, despite the fact that they are significantly more expensive than expanded polystyrene. Their main technical limitation is the fact that they are more likely to absorb water than expanded polystyrene, an......

5. Thermal insulation materials, technical characteristics and selection criteria

Figured you would be glassing over this foam, especially since your post said "I'll be joining two slabs of foam", which implies gluing two blocks together. It would be kind of not a smart thing to just slather epoxy on foam and use that as a refrigerator wall. You need to glass it.

[singlespeed]

Working in a confined space with epoxies is different from working outside. The warnings that should accompany the containers of epoxy and hardener should not be taken lightly. Opening all available hatches and the companionway, with large fans will help with fume buildup, but you personally will need mask with a source of constant clean air.

[robwilk37]

what are your plans for the final interior coating for the tanks? im not aware of an NSF compliant small tank coating. i built integrated tanks too but in the end had to fit custom bladders for potable water...

[coopec43]

Originally Posted by robwilk37

what are your plans for the final interior coating for the tanks? im not aware of an NSF compliant small tank coating. i built integrated tanks too but in the end had to fit custom bladders for potable water...

The "tanks" they are talking about here are fridge/freezer boxes.

As far as potable water is concerned epoxy is not considered safe. I used a water based bitumen which is certified as " safe" according to the appropriate standard.
Exterior Grade Brushable Waterproofer: Waterproofing: Crommelin


Clive

[Wotname]

Originally Posted by coopec43

.......

As far as potable water is concerned epoxy is not considered safe. I used a water based bitumen which is certified as " safe" according to the appropriate standard.
Exterior Grade Brushable Waterproofer: Waterproofing: Crommelin


Clive

Really??? I understood there are various food grade epoxies used in the food manufacturing industry (and in wine making etc) but I could be wrong so I am interested in knowing more.

The link definitely states the product is suitable for rainwater collection but I wonder if it is OK when permanently immersed?

Curious and not wishing to hi-jack the thread.

[john61ct]

Yes, epoxy for potable water storage is dicey, lousy taste at best.

Bladders, or check out Ronco Plastics

[robwilk37]

the OP was for "integral water tanks", thats why i asked. the link concerns only water collection and not storage, the NSF specs for the two are quite different. water storage specs are volume dependent and usually certified "safe " for large storage tanks (several thousand gallons) and not small boat-sized tankage. then theres the problem of rain water vs RO off the watermaker which is a bit more "active" and can leach nasties from the coating.

i love the idea of integral tanks, but its not as straight-forward as it seems...

my .02, sorry to hijack.

and yes, epoxy sticks to polyurethane.

[coopec43]

Originally Posted by Wotname

Really??? I understood there are various food grade epoxies used in the food manufacturing industry (and in wine making etc) but I could be wrong so I am interested in knowing more.

The link definitely states the product is suitable for rainwater collection but I wonder if it is OK when permanently immersed?

Curious and not wishing to hi-jack the thread.

Wotname

I tried to copy the actual statement in their brochure where it says " Suitable for collection and storage of potable water" but nothing is working this morning.

http://www.crommelin.com.au/assets/U...umen-Paint.pdf

Regarding epoxy for drinking water I'm quite sure you and John61ct are correct. (I don't know about robwilk37 as he is way over my head!)

Apparently epoxy is OK for storage of water if it is cured properly in optimal conditions but who of us can do that on a yacht?

The Gougeon Bros (WestSystem) do not recomend it.


Why we don’t recommend building an epoxy composite tank for potable water

We have adopted the broad policy of not recommending epoxy for drinking water tanks because of regulatory and safety issues. The potential problems outweigh the benefits. To date, none of Gougeon Br......

https://www.epoxyworks.com/index.php...nk-guidelines/

[qwert]

Don't know about water tanks but I epoxy glassed over polyurethane foam for my fridge and was left with a strong epoxy 'flavour'. Completely fixed with a two part norglass product. Give them a call, you get to talk to the scientist who designs the paint, in my experience if one of his products isn't suitable he will tell you.The one I used was perfectly odourless (once dry !)