Pour Foam Strategy Questions

[Stimputello]

I was wondering if anyone had advice on pour foam in the subfloor and avoiding poultice corrosion?

I’m building a custom 14ft V-Hull into a Poling skiff and am trying to figure out how to foam the subfloor. The boat does have sloping sides that will drain cleanly to a channel in the middle which is great for me. I know closed cell foam will trap water between the foam and the hull, eventually cause poultice corrosion.

Here’s my original plan… Etch hull, zinc chromate primer, two thick coats of epoxy bilge paint, cut plastic tubing for extra drainage in the foam then attach to every rib (lowest side closest to the transom), then pour in foam. I am worried however that eventually the foam will slightly saturate and cause water to eat away at the hull. I do know that aluminum fuel tanks have a long life-span when coated in a similar way and those are CASED in foam usually.

This is where I get confused… I have talked to some builders that recommend not putting any foam in the subfloor, to prevent all poultice corrosion. Instead, foaming above the subfloor in compartments will prevent water getting trapped against the hull entirely. Makes sense to me, but I personally don’t like the idea of no foam under the subfloor.

Any thoughts on this? I have a tendency to overbuild things, so all opinions are welcome . I’d love to just prime it, paint it, then continue building/framing this thing out.

 

[Stimputello]

I did have a buddy of mine recommend even laying a 6mil plastic sheeting before pouring foam to allow space between the hull and foam to vent. Personally, I really like that idea…

 

[LDUBS]

I did have a buddy of mine recommend even laying a 6mil plastic sheeting before pouring foam to allow space between the hull and foam to vent. Personally, I really like that idea…

Good stuff. There is a step-by-step of what you describe in this thread by @onthewater102:

https://www.tinboats.net/threads/1985-tracker-iii-restore-conversion.45323/post-457780

Additionally in a more recent thread @thill mentions good results from using Tyvek house wrap:

https://www.tinboats.net/threads/tyvek-house-wrap-under-decking-and-over-pour-in-foam.50217/

 

[Stimputello]

Good stuff. There is a step-by-step of what you describe in this thread by @onthewater102:

https://www.tinboats.net/threads/1985-tracker-iii-restore-conversion.45323/post-457780

Additionally in a more recent thread @thill mentions good results from using Tyvek house wrap:

https://www.tinboats.net/threads/tyvek-house-wrap-under-decking-and-over-pour-in-foam.50217/

Tyvek huh? I really like that idea, actually sounds like it might be the best option there is and ease of use is super simple. I’m gonna give that a shot, thanks so much!

 

[SAABologist]

Good stuff. There is a step-by-step of what you describe in this thread by @onthewater102:

https://www.tinboats.net/threads/1985-tracker-iii-restore-conversion.45323/post-457780

Additionally in a more recent thread @thill mentions good results from using Tyvek house wrap:

https://www.tinboats.net/threads/tyvek-house-wrap-under-decking-and-over-pour-in-foam.50217/

My 1987 Mirrocraft had the original foam poured over a plastic sheet.

 

[thill]

I've had boats with plastic sheet laid before the foam pour, and that worked great.

It doesn't look like you have much depth to work with. In that case, I would probably fit sheets of closed foam on the bottom and then pour over them. That will give you drain space and prevent any interaction between the foam and hull. Then house wrap over the top to prevent any saturation. (I went with a different brand than Tyvek, one that matched the original better)

You should be great for many years with your plan. I hope it goes great for you!