Curing problems with FGH 2lb PU Foam

I’m hoping those of you with experience working with FGH’s two-part PU foam can help me out with this. I’m currently manufacturing some paddles and my plan is to do the production run by molding my own foam cores into the shape I need already. I made the silicone master mold from one of my plugs and it came out great. I purchased some 2lb two-part PU foam from Fiberglass Hawaii and had it shipped over. I’m a pretty keen mixer and the foam isn’t rubbery so I know my 1:1 mix ratio is correct, however when the foam finally cures it’s incredibly brittle, to the point where little pressure on the surface reduces the entire core to dust. The stuff just sloughs away. I’ve been shaping long enough to know what PU foam should feel like at any density and this definitely isnt it. I spoke with Wade over at the Ventura store and we’re thinking it may be an elevation issue.

I currently no longer live on Maui and I’m in SW Colorado instead. I’m above 7,000ft and the temperature regularly drops to between 2-15 degrees at night. I mitigate the temps with a shop heater to keep my workspace at room temp, and Wade says the cold should really only affect the curing time and not the consistency. We’re thinking maybe the 2lb density has issue curing at elevation, kinda like baking cookies. 

Can anyone with experience mixing foam confirm or shed some light onto that for us?



Have you tried contacting Fiberglass Hawaii about it? That would be my first step. Wqade in the Ventura store is very knowlegable.

Surfboard blanks are made with a foam that expands inside the mold and creates tremendous pressure. Thats why the molds are made of concrete.  Your silicone mold isnt going to give you that result.  Perhaps try 4 pound foam. 

Or mix epoxy, microballoons, and pour it into your mould. More expensive, but stronger and just as light

Yeah that’s actually mentioned in the second paragraph - that’s what’s sort of leading me to believe that it’s the elevation

When I spoke to wade about it, we decided it’s not a density issue in that respect, because even if the foam isn’t constrained by the mold to manipulate the density, the 2lb foam left in a bucket to freely expand into a mushroom still should’t be so brittile that it turns to dust when you apply light pressure to it. We’re thinking it’s more like trying to bake cookies at altitude - less atmospheric pressure may be allowing more space to form between the crystals and therefore preventing them from atually bonding with each other the way it’s supposed to, so what I’m making is essentially PU powder rather than a bonded foam. Theoretically the sillicone mold (with metal plates on both sides and strapped to keep pressure on the two halves) should work just fine since this is the same method FX shops use to make movie and stage props. 

Unfortunately their next density is 8lb, and I’m doing this to make ultralight paddles so hopefully moving up to that density won’t increase the weight as much overall. The structural integrity is coming from the carbon exterior while the foam core is simply to provide the shape without having a fully hollow paddle blade. It seems like a higher density is going to be the next step, we’re just curious if anyone else has had this happen while working at altitude. 

Somehow I find it hard to believe I’ll achieve the same weight as a foam paddle core using any ammount of epoxy and microballons - aside from the fact that that much epoxy in a confined space would most likely start a nuclear reaction (lol) the nature of epoxy and microballoons would make them heavier (which would be why at a certain size using filler for a repair will make your board float lopsided)- I’ve mixed up some pretty dry mixtures and they’re definitely not as light as foam, and I’ve found that after a certain point using too may microbaloons will hinder the epoxys ability to cure properly. 

Or were you saying mix the epoxy/microballoon slurry in with the expandable PU? 

Not saying you’re wrong, just saying that in my experience I’m doubful that will achieve the same weight (that’s not to mention the cost of that would make a production run phsyically impossible)

Rather than silicone, can you make your mold using concrete/cement?  Might give you better pressure control.  I do not have any concept about how stiff/solid your silicone mold is.

EDIT:  My “guess” would be lower atmospheric pressure is the main culprit.  Temperature may further compound the problem.

There isn’t much that Wade at FGH doesn’t know. He is well versed on all of their products. Most likely, he gave the right reason.

Another thought for  you. I receive emails from a company named Freeman Manufacturing. They sell materials for the mold manufacturing industry for making “parts”. Maybe they can help you.

Unfortunately cement is a no-go based on how light I need the core. I’m sure if I were building pressure and making this like a surfboard blank it would work, but my first mold was actually solid fiberglass and it came out great, but the unfortunate part was the part isn’t strong enough to demold from a rigid mold, it just breaks. I switched to silicone (it’s Mold Max 1400nv so it’s actually really dense) so I could demold by peeling the mold away, plust the release properties of silicone make it a no-brainer. 


I’m clamping the mold between two pieces of steel. Previously I had only put in enough foam to expand into the shape and stay light, this coupled with atmospheric pressure I think prevented the crystals from bonding properly. Last night I tried again and I severely overfilled the mold so that it mushroomed out the vent hole big time (wasteful but it was a test). This managed to build up a considerably larger ammount of pressure inside the mold (closer to a surfboard mold) and the part came out perfectly. Downside is it’s heavier than I wanted, plus side is it’s perfect. Using only slightly more foam than required to expand into the mold should get me the pressure I need to make it solid without wasting so much and making it SO dense. We’ll see I guess. 

I had actually talked to one of those companies before I started making my own. I was going to have them cast me either a steel or HPDE mold for the blades… three “tools” (a tool being one mold for two blades) were quoted at upwards of $25,000 so definitely way outside my budget range lol

My cousin has a business making composite parts for motorcycles.  His process would be very much the same as you’d want for making a paddle.  Its done inside a female mold.  There are videos showing the process on youTube you should check out for ideas.