Recommendations for two part closed cell foam needed

[Bman1056]

I am replacing the floor in my bass boat and have found that the foam is holding quite a bit of water. I'm sure a lot of you have your opinion as to which is the foam to use. Please share your thoughts.

 

[tpenfield]

2-part pour-in urethane foam would be my choice because of the structural integrity that you will get.

The foam does not readily absorb water, but if water fills the chambers from other issues, it will eventually (years) end up in the foam.

 

[sheboyganjohn]

Any 2 part urethane foam. 2# foam should be just fine. If the foam is structural you could go to 4#, but 2# is what just about everyone uses for floatation.

 

[Bman1056]

Thanks guys.
I think 4# is going to be my choice. I found U.S. Composites in Florida which seems to have the best pricing.

 

[snowman48047]

I just pulled 600lbs of wet 2 part out of my Lund.

 

[ondarvr]

Not sure why people go with 4#, other than if the 2 is good, 4 must be better thought process.

​2# is what 99.999% of the builders use, the only reason I don't say 100% is because I'm sure there is one or two out there that do use 4#. They are they same, only the small cell structure of the 4# means twice as many of them, it also means twice the weight and cost. It will still absorb water, just at a slightly slower rate due to the number of cells. So you start out with twice the weight, then over time, maybe a very long time, the 2# may increase in weight and catch up with the 4#, this will most likely be long after the boat has moved on the next owner or the land fill.

 

[gm280]

I would forgo the 4lbs mix and pour for the 2lbs mix and pour. Why add more weight for noting in return? :noidea:

 

[Baylinerchuck]

Not sure why people go with 4#, other than if the 2 is good, 4 must be better thought process.

​2# is what 99.999% of the builders use, the only reason I don't say 100% is because I'm sure there is one or two out there that do use 4#. They are they same, only the small cell structure of the 4# means twice as many of them, it also means twice the weight and cost. It will still absorb water, just at a slightly slower rate due to the number of cells. So you start out with twice the weight, then over time, maybe a very long time, the 2# may increase in weight and catch up with the 4#, this will most likely be long after the boat has moved on the next owner or the land fill.

I chose to go with 4 pound foam since my foam was structural, and due to the amount installed by the factory it was pretty clear that it wasn't there for floatation. I have a wobble roller trailer in which the rollers contact the hull in the cavities that get foam. I was worried that 2 lb foam could cause depressions in the hull due to the weight of the boat being concentrated in small areas. My boat also only has 2 stringers which in my opinion was more of a case for the higher strength foam. Based on US Composite's specs I felt the 4 lb was the better option. Is that what the factory used? Hard to know exactly. In my opinion the foam you choose should be totally based on the application. So you are getting something in return for that little bit of weight. In our restorations everything else is built better than the factory, why not foam. Just my opinion.

 

[Baylinerchuck]

Oh BTW, I searched high and low. US composites is definitely the place to go for foam. No other site has better pricing including the shipping.

 

[JASinIL2006]

Just be sure to be mindful of the temps. It kicks off much much sedately when you're at the lower end of the indicated temperature range, and much more vigorously at the high end. Your foam will go farther if you pour it on a very warm day, but it will kick off quickly.

 

[ondarvr]

I chose to go with 4 pound foam since my foam was structural, and due to the amount installed by the factory it was pretty clear that it wasn't there for floatation. I have a wobble roller trailer in which the rollers contact the hull in the cavities that get foam. I was worried that 2 lb foam could cause depressions in the hull due to the weight of the boat being concentrated in small areas. My boat also only has 2 stringers which in my opinion was more of a case for the higher strength foam. Based on US Composite's specs I felt the 4 lb was the better option. Is that what the factory used? Hard to know exactly. In my opinion the foam you choose should be totally based on the application. So you are getting something in return for that little bit of weight. In our restorations everything else is built better than the factory, why not foam. Just my opinion.

​It was there for flotation, with a side benefit of stiffness, don't confuse stiffness with strength. Those boats had 2# when new, and they held up for decades, even with soaked foam and rotten wood. There is a chance that if your hull was on the thin side, then yes 4# would hold up better for a while, but those benefits would be down the road when the 2# started to break down, and then only while the 4# was still in good shape, so you end up in the same place. The chemistry of these foams isn't great, so in new construction it's not considered in any strength calculations of the hull.

​For the most part it's the "feel good" method of construction, if 2 is good, 4 must be better, so 8 should be great. If these hulls failed in a way other than rotten wood, then maybe there would be a need for 4#.

​Foam is rated at 77F in a free rise situation, low temps result in less rise and higher density, when you put it in an enclosed space it can't expand as easily, so the density is also higher, it will expand more with high humidity. So normally the density in the hull is higher than what the actual weight of the foam is.

​The only real downsides of 4# is the weight and cost, if you're fine with that then it's not an issue, it's the mindset that it must be better because it a higher weight that bugs me.

 

[Baylinerchuck]

​It was there for flotation, with a side benefit of stiffness, don't confuse stiffness with strength. Those boats had 2# when new, and they held up for decades, even with soaked foam and rotten wood. There is a chance that if your hull was on the thin side, then yes 4# would hold up better for a while, but those benefits would be down the road when the 2# started to break down, and then only while the 4# was still in good shape, so you end up in the same place. The chemistry of these foams isn't great, so in new construction it's not considered in any strength calculations of the hull.

​For the most part it's the "feel good" method of construction, if 2 is good, 4 must be better, so 8 should be great. If these hulls failed in a way other than rotten wood, then maybe there would be a need for 4#.

​Foam is rated at 77F in a free rise situation, low temps result in less rise and higher density, when you put it in an enclosed space it can't expand as easily, so the density is also higher, it will expand more with high humidity. So normally the density in the hull is higher than what the actual weight of the foam is.

​The only real downsides of 4# is the weight and cost, if you're fine with that then it's not an issue, it's the mindset that it must be better because it a higher weight that bugs me.

Thank you for your reply. Please don't take my replies as arguments, I'm trying to glean as much information from you as possible given your experience. I think this a great thread to air this out a bit. My 20' Chap only had, (has) 10 cu ft of foam in it, which is why I didn't think floatation was the primary factor for the foam, especially in a 2650 lb boat. The brochure from the same year states "structural pockets are filled with foam for more strength". Granted this is a sales brochure. As I think about how the rest of the boat was built, I'm pretty sure what was in there was 2lb foam.....they ain't built to last forever. I really put more thought into it that it feels good.....though in the end, and admittedly so, it does. Ha ha.

One tip if I may based on your statement of full expansion. I warmed up my two part mixes prior to use. I also inserted a heat gun into the cavities to warm them prior to the pour. All this to ensure full expansion of the two part system.

I didnt see the added weight as a major detractor given I only used 10 cu ft. I will admit, price was a consideration since 4lb is in essence twice as expensive per volume compared to 2 lb.

 

[tpenfield]

I think the 4 lb foam is a USCG requirement of fuel tank installation ( for tanks that are foamed in). Otherwise, the 2 LB is fine IMO.

 

[gm280]

Certainly not trying to argue with anybody about this subject. However, if you ever used mix and pour foam, you would believe how strong a void becomes with 2lbs foam. I mean if you were to stand on a chamber and poured in the foam, you would understand quickly how solid that void becomes. I was amazed to see it myself. I used 1/2" plywood for my floor in my boat project. But if I has to do over, I would go with 1/4" plywood because of the fiberglass and poly but also the 2lb foam added underneath. It does add that much structural integrity to the floor. I am not trying to talk you out of what you decided, but merely telling you about what I discovered. JMHO

Oh, and you really have a lot more time then you think when mixing the mix and pour foam. It starts expanding in about 45 seconds. And that sound like you have to work really fast. But 45 seconds is longer then you think. It also gets pretty hot when mixed. I would certainly mix up a small test batch before doing the real project so you can see how it kicks off and when.

 

[ondarvr]

Thank you for your reply. Please don't take my replies as arguments, I'm trying to glean as much information from you as possible given your experience. I think this a great thread to air this out a bit. My 20' Chap only had, (has) 10 cu ft of foam in it, which is why I didn't think floatation was the primary factor for the foam, especially in a 2650 lb boat. The brochure from the same year states "structural pockets are filled with foam for more strength". Granted this is a sales brochure. As I think about how the rest of the boat was built, I'm pretty sure what was in there was 2lb foam.....they ain't built to last forever. I really put more thought into it that it feels good.....though in the end, and admittedly so, it does. Ha ha.

One tip if I may based on your statement of full expansion. I warmed up my two part mixes prior to use. I also inserted a heat gun into the cavities to warm them prior to the pour. All this to ensure full expansion of the two part system.

I didnt see the added weight as a major detractor given I only used 10 cu ft. I will admit, price was a consideration since 4lb is in essence twice as expensive per volume compared to 2 lb.

​It's not an argument or anything like that, The foam used is sort of like the resin type, in the long run it doesn't make that much of a difference, some people just "want" to use epoxy, they just feel better about it, which as you said, is what it's all about. At times I tend to answer not for the current situation, but so that future readers don't get the idea that a certain product is required for use or the project will fail.

 

[kcassells]

Hey.... ya know on the EEEEEEEEEEEEEppppoxy comment. :watermelon:
I enjoy all your comments Ondarvr.

 

[ondarvr]

In some types of construction the part can easily be strong enough to function as designed, but it may flex, the flex is perceived as the part being weak, so they need to find a cheap way to make it stiffer, foam is frequently used in this way, it doesn't make the part any stronger, but it feels that way. Hull sides frequently flex more than what feels right, so foam is used to eliminate the flex, plus it's counted as flotation, so they get an additional benefit.

 

[Slager]

ondarvr
While we're talking about foam, what's your opinion on drilling limber holes in sealed foam filled cavities? Worth it or a waste of time?

 

[ondarvr]

Best case you would have hollow stringers with numerous limber holes so the water could flow freely to a spot where it can be removed easily. The foam would be contained in sealed plastic bags and held up off the hull a couple of inches so water can pass under it. This isn't as hard as it may seem, and the cost would be about the same as other methods, it would just take a little extra thought and time (not much) to do it this way.

 

[sheboyganjohn]

Personally I like the fully sealed chambers for foam. If I cannot open it completely up to dry, I want it sealed. The key is that once sealed you cannot put any holes, including screws, into it. If you want to connect to it, attach via PB a sacrificial piece of wood that you glass into place. Use this to sink screws into. If, or I should say when, it starts to rot, you just remove the piece of wood and put a new one in.