Replacing Flotation Foam

[Sleestack]

When replacing an old floor and old, saturated flotation foam with the 2-part expanding stuff, is it best to actually lay the floor first and use a hole saw to cut a hole to pour the mixture in and hope everything is good to go and fills everything in or should I fill the voids first, trim any overage then lay the floor? I've seen a YouTube video where the guy cut the hole, but he was unsure whether or not he was completely filling the voids. First timer with this stuff and I'd like to do it right. Any thoughts?
Thanks

 

[alldodge]

Lay the floor, cut holes and pour in the foam
Do place heavy weights on the deck so it has "less" a chance of busting the deck up

 

[Lectro88]

The other thing you can do is pour with the hull in an aggressive incline.
make sections rather than try and do full width and length.

 

[froggy1150]

I stood mine up at around 30ish degrees. Maybe more. The holes were placed to be above where the foam would land and expand up to hole, then cover and weight hole plug. Pour in next hole and work my way up. I also left little gaps In the tabbing along the sides of the hull to allow the air to vent so the foam made it all the way to the sides. Then I cleaned the foam that did come thru vents and filled I shed tabbing

 

[froggy1150]

"And finished tabbing"

 

[Chris1956]

So he should put heavy weights on the deck to lessen the chance the floor will get busted up by the foam? What sense does that make?

Also, what is advantage of cutting holes in new deck to pour the foam in, and then repairing them? Also makes no sense.

Pour the foam, let it cure, cut off flush with stringers and install deck. A old fashioned hand saw can cut it real flush, with minimal effort.

 

[tpenfield]

I have seen it done either way. The challenge is to fill the chambers as completely as possible. That you can do with foam filling before the floor goes down. then it is a matter of getting the floor to adhere to the structure.

With the floor installed and drilling holes, the problem is trapped air preventing the foam from expanding to fill the chambers. As a remedy you could drill smaller holes in all 4 corners of each chamber in addition to the larger hole. That way air will escape and you will have a sense of if the chamber got filled (not sure what you would not if it fell short though . . . )

Another thing to consider is the volume of each chamber and pour in a fairly precise amount of liquid foam for each. Regular 2 lb. foam expands 30X its liquid volume, 4lb. expands 15X and so forth. These are maximum expansion ratings (usually based on 85˚ F pouring temperatures), so heat is your friend in this situation. Hot summer days are great for foam pouring. Colder temperatures will get less expansion, so figure that into your material needs.

So, if you were filling a 2 cu. ft. chamber (which is about 15 gallons) you would want to pour in at least 1/2 gallon of liquid . . . maybe a bit more (assuming 2 lb density foam). I find that it is easier to have the liquid pre-measured for each chamber in separate containers and mix/pour as you go.

Remember . . . you get about 30 seconds of mixing time and 15 seconds of pouring time until the liquid starts expanding into foam.

 

[Wildey]

Pour the foam, let it cure, cut off flush with stringers and install deck. A old fashioned hand saw can cut it real flush, with minimal effort.

Is there any truth to earlier posts suggesting that shaving the skin off of the foam exposes / opens cells that will then take on water ? ? compromising the entire pour of that section ?
Getting mixed reports ....... just wondering as I am near to that point as well.
Thanks for clarification.
W

 

[tpenfield]

It's true . . . the biggest culprit is the trimming around foamed-in tanks. Morning dew from the daily temperature cycling will tend to drip right onto the exposed/cut areas of the foam that surrounds the tank. The moisture (water) does find its way in between the closed cells of the foam and works its way downward.

Uncut foam is way better in that regard . . . much more water resistant.

As for foaming the hull structure of a boat. . . a coating of resin over the cut areas of the foam takes care of the issue.

I wish boat manufacturers would do similar around the fuel tanks.

 

[kcassells]

Is there any truth to earlier posts suggesting that shaving the skin off of the foam exposes / opens cells that will then take on water ? ? compromising the entire pour of that section ?
Getting mixed reports ....... just wondering as I am near to that point as well.
Thanks for clarification.
W

USComposites reads foam as;

14. Is this foam water resistant?

Yes, but with the following caveat. The foams that we sell are considered closed-cell, which means that each cell that makes up the foam structure is completely closed off from surrounding cells which prevents it from acting like a sponge. It is completely safe for this foam to be in contact with water for hours/days/weeks and even months with no adverse effects. However, it should never be submerged in contact with water permanently. Over a period of years the water contact can begin to soften the foam and cause it to lose its closed-cell status. This foam is designed primarily to be used as an insurance policy in case of damage/holes that could cause a vessel to lose buoyancy. Pinhole sized openings would essentially have no effect on the foam since the amount of exposure is so minimal but you should always make repairs as soon as possible to keep the foam effectiveness as good as possible. This will be the case with all after market closed-cell polyurethane foams and even manufacturer installed foams.

 

[Wildey]

The moisture (water) does find its way in between the closed cells of the foam and works its way downward.

Uncut foam is way better in that regard . . . much more water resistant.

As for foaming the hull structure of a boat. . . a coating of resin over the cut areas of the foam takes care of the issue.

Thank you.
When gutting my Capri, I noticed much of the foam, especially under the seat boxes, was poured in a polyethylene bag, or liner. It popped loose from the hull structure quite cleanly. It was evidently for pure flotation, not structural (I assume)
Thanks again,
W

 

[Wildey]

USComposites reads foam as;

14. Is this foam water resistant?

Yes, but with the following caveat. The foams that we sell are considered closed-cell, which means that each cell that makes up the foam structure is completely closed off from surrounding cells which prevents it from acting like a sponge. It is completely safe for this foam to be in contact with water for hours/days/weeks and even months with no adverse effects. However, it should never be submerged in contact with water permanently. Over a period of years the water contact can begin to soften the foam and cause it to lose its closed-cell status. This foam is designed primarily to be used as an insurance policy in case of damage/holes that could cause a vessel to lose buoyancy. Pinhole sized openings would essentially have no effect on the foam since the amount of exposure is so minimal but you should always make repairs as soon as possible to keep the foam effectiveness as good as possible. This will be the case with all after market closed-cell polyurethane foams and even manufacturer installed foams.

I've seen that as well, thanks.
Also read that once wet/compromised, freeze/thaw cycles can greatly accelerate the progression of the saturation.
Thanks,
W

 

[alldodge]

The foam adheres to the deck


https://forums.iboats.com/threads/chrylser-105-conqurer.657617/page-3

 

[JASinIL2006]

It never made much sense to me to pour in closed cell foam and then cut it open over much of of its surface area. It is really quite simple to get pretty complete expansion into under deck cavities, and it's also pretty simple to seal the holes needed to pour in the foam and the relief holes.

I think the idea of filling cavities in stages (rather than trying to fill them all at once) makes sense, because the real problem could be overfilling with foam. Temp and humidity have a great effect on the expansion rate of the foam, so pouring in stages also lets you gauge better how much you need to fill each cavity.

 

[Sleestack]

Thanks for all the replies! I think the way I'm going to go is to install the foam first. I like the idea of being able to actually eyeball what's happening and there will be no way for me to possibly destroy a new floor. As far as trimming, according to the stuff I have, it can be coated with any type of polyester, epoxy or vinyl ester resin without melting so sealing won't be a problem. Again, thanks for the help deciding

 

[Baylinerchuck]

Pouring the foam after the deck is installed in small controlled batches is the only way to fly. If you use a hole saw to cut the holes, those pucks can be glued right back in with reinforced thickened resin. Then go over the entire floor with CSM. Heck, two layers or more of CSM or 1708 was gonna happen anyway over the plywood floor. I personally didn’t use weights as my pour was done in small amounts with the boat tilted from the bow to the stern so the foam ran forward. I got very good results with the US Composite foam this way.

 

[froggy1150]

Also foam is sticky and when poured into an assembled deck it bonds to the hull and deck and stringers making one solid thing

 

[chevymaher]

I cut the holes. Slight incline. Did not tab in the deck. Poured. When full put the plug in set a brick on it. As long as it has a place to run to and escape there is no pressre to speak of under the deck. Once it is full there is the magic zone it is soft enough to cut. Once hardened I wire brush and drill to clean it up. Then tabbed the deck down and laid the glass on top.

 

[alldodge]

BTW, I put weights on my deck because I used 4 LB foam. Its made for fuel tanks but I wanted to use this type for more rigidity instead of 2 LB

 

[Baylinerchuck]

BTW, I put weights on my deck because I used 4 LB foam. Its made for fuel tanks but I wanted to use this type for more rigidity instead of 2 LB

I used the 4lb foam too. I wanted the extra structure since my Chap doesn’t have much under the deck.