Foil insulation, what glue?

[JustinT]

What glue should I use for foil insulation?
Thanks. Justin.

[tkeithlu]

Single layer of foil, used as a infrared reflector? Glued to a smooth hard surface? Spray-on contact cement comes to mind. Spray both surfaces, let it gum up, and slap those suckers together.

But really, you could be talking about bats of fiberglass with foil surfaces, or some other "foil insulation," and you might be talking about a high heat situation, so could you clarify?

[JustinT]

Basically putting foil insulation on the fiberglass walls on the inside of the the boat.

[LakeSuperior]

Are you trying to prevent condensation up there in the cold damp country? If so the foil glued to the fiberglass will be of very minimal value solving that problem. In fact, it will make the condensation problem worse. You need a conduction barrier like a stick on foam layer.

What happens is the cold temperature from water conducts through the fiberglass cooling the inside or cabin side surface of the glass. If this temperature is below the dew point then you will get condensation.

Think of the the glued on side of the foil being just part of the fiberglass or thermal conductor. The glued on side of the foil doesn't act as a thermal insulator. However, the cabin side foil surface reflects most of the radiative heat and therefore the surface of the foil will actually remain colder giving condensation at a higher cabin temp.

You may know all of this and this may not be the problem you are solving so it's FWIW.

[JustinT]

Well, it was more for warmth, but I was hoping it would stop condensation a little I must admit.

[Thumbs Up]

Do you mean Reflectix? The shiny bubble wrap. Not a foil but is an aluminized plastic. It does have an r value so should help some. I would try carpet tape which is an industrial strength two sided adhesive tape.

[JustinT]

Yes, I have Alreflex 2L2. Sorry, foil was misleading. Tape is an idea, but not sure if sticky enough.

[Thumbs Up]

Looks like they are recommending this BR tape. Which looks like a thick black double sided tape.https://www.thermal-economics.co.uk/...-bonding-tape/ . Another idea is using adhesive backed velcro.

[blu3534]

Originally Posted by JustinT

Basically putting foil insulation on the fiberglass walls on the inside of the the boat. ..
Well, it was more for warmth, but I was hoping it would stop condensation a little I must admit.

[Edit: sorry only now read that you already have alreflex. Thus my Armaflex reply is "quite stupid" ]

I believe you would need to use Armaflex (or something similar) to really get an insulation effect. There is adhesive-backed Armaflex. (Don't use the cheap ACE under no circumstances, XG is recommended (or an even more expensive one with microbiological treatment)

Unfortunately I don't know currently how thick the layer would need to be that condensation/dew point "works"? There are camper van videos where people line the "whole box".

[LakeSuperior]

Originally Posted by blu3534

[Edit: sorry only now read that you already have alreflex. Thus my Armaflex reply is "quite stupid" ]

I believe you would need to use Armaflex (or something similar) to really get an insulation effect. There is adhesive-backed Armaflex. (Don't use the cheap ACE under no circumstances, XG is recommended (or an even more expensive one with microbiological treatment)

Unfortunately I don't know currently how thick the layer would need to be that condensation/dew point "works"? There are camper van videos where people line the "whole box".

Eliminating condensation is a moving target. Depends on relative humidity and air and/or water temp (depending if the exterior surface is above or below the water.) That is why wooden boats tend to be less damp inside in cold climates as the wood is a better insulator than glass.

To defeat condensation you are adding insulation so that the interior surface temperature of the insulation stays above the dew point. Technically you would need to figure out all of the RH and climatic conditions and design for worst case to defeat. However, you really want to reduce so I would pick a foam thickness that is easy to work with like 6 mm for example.

The interior temperature of that surface mostly depends on the conductivity of the fiberglass hull and the conductivity and thickness of the layer of insulation you are adding. Recognize that there is a thickness where you end up with diminishing returns in terms of cost and pain to install.

[Pete7]

Originally Posted by JustinT

Basically putting foil insulation on the fiberglass walls on the inside of the the boat.

You will to have an air gap for it to work properly as the foil reflects the radiated heat back into the boat.

The closed cell insulation like camping mats would be easier to install if its going to touch one or more surfaces.

Pete