I’m using EPS blanks and want to install high density foam inserts to better support my finbox installs - weight is not an issue. The idea of using 8# density pour foam in the cavity from bottom to deck (prior to shaping) to really lock those boxes in really appeals to me, so I’m inquiring about potential drawbacks.
At that density what are my chances for running into overly large air bubbles or brittleness?
Will the foam flex enough to not snap when it gets stressed?
Should I expect any difficulties with adhesion with the EPS?
I use the pour foam from Aeromarine in San Diego for installing all embeds in eps, and also as a filler for deep repairs. There is no exotherming with the stuff I have, and it’ll stick to anything. The problem is that you have to clamp everything down, and make sure it’s aligned, so you can’t just hold it down with weights (well maybe leash plugs). Pour foam density has more to do with the cavity it’s injected to. If you don’t have around 85% containment, it just flows out the opening and the densities become the same. I use either 2 or 4 lb density. The trick to working with it is mix real good, use no more than 1 oz total at a time, and spread it while it’s still in the liquid state. It also makes a mess, so tape off a big area around your hole. You only have about 30-40 seconds before it goes off, so have everything ready before you mix it. For a regular center finbox, just pour it in and spread it around all the surfaces, drop in the box (with a piece of wood for alignment wedged in), and clamp across the front and rear of the box with strips of wood and quick-clamps. Use good size pieces of 1/8" masonite or ply on the opposite side so the clamps don’t bite into the foam. You’ll have about a minute to fiddle with alignment until the foam gets too hard. After about 10 minutes, remove the clamps and clean up with mess. Trim off any pour foam to flush with the surfaces (small saw, razor knife). There will probably be a lot of blow-holes, so smash the foam into the hole with a mixing stick and overcoat with a slurry filler. I do this step when sealing the blank. What I’ve described may seem like a hassle when reading it, but in practice it’s very simple and only takes 15 mins tops. It’s much more secure and reliable than trying to do consecutive pours with epoxy + filler and all that time for curing and exotherm problems. Once it’s fully cured, it’s almost as strong as using routed D-cell inserts. My own experience with D-cell inserts is that there’s a big problem with the epoxy draining into the blank (poor bond), and you still have an exotherming issue. I originally was using the pour foam for the inserts, but found over the years it was just as strong by itself.
I’ve used the FGH pour foam numerous times and freezing it will solve that problem. After the pour you can wrap the area in saran wrap and push it back when it expands to create a higher density. When it kicks it kicks fast but freezing it delays the kick long enough to make it work well.
Edit to say it does not actually freeze in the freezer…
Was thinking that three round foam plugs with the middle one overlaping the other two would work for a probox type box. An other option would be an epoxy that dosn’t exotherm.
There’s so much variance in those PU foam kits that testing would be advised before proceeding with any of them. IMO cutting inserts out of better quality controlled-blow foam is always going to be a better solution, if you’re determined to use inserts.
I’m gonna bump this cause I’m in the exact same boat as gdaddy, except that I have already bought a 2-quart kit of 8-lb foam. I didn’t realize exotherm was an issue. Hasn’t PeteC mentioned using it?
I got a test block of 2-lb foam to try it on first. I just haven’t made my router template yet.
Thanks guys, that was the input I was looking for.
Resin adhesion to the Probox has never been an issue so far, although I have had problems with exotherm in EPS due to the amount of resin around the box and my use of regular hardener on a warm day. I ended up with some leaking on one board between the resin and the foam due to contraction of the former.
That was before I went to the PU inserts. Since then they’ve been rock steady.
In reference to using a hole saw for the round plugs I’m not fond of FCS plugs but if I was going to use those I’d use that method as well.
Any reason not to make round pu foam plugs like in yorkys thread?
Pretty sure he just uses a two holesaws, like patching a hole in the floor. If you get the size right shouldn’t need any glue. Pre drill a template so you can take the bit put of the hole saw when you cut the plugs.
Thanks for the input, and I was planning a test panel to check for exotherm and bonding with a 1.5# or 2# EPS blank. I’m using a through-glass Pro-Box install (no flange) with a cap over that. Do you think if I spiked the cavity for the box install that bonding might still be marginal?
I’d run a test panel first, to see if the exotherm of foam blowing (or the expansion) produces any ill effects.
But I’d also be wary of bond strength on high density PU. You don’t say if you’re doing plugs or a flange system; if its a flange I’d stay away from anything higher than 6lb PU, higher densities have notoriously poor bonding properties.
edit to add that it won’t be any fun to shape either if you do it the way you’re talking about.
Thanks, but I was already aware of these other options. I already have some 4# PU skimboard foam on hand with which to build inserts. I’d prefer to use that stuff over Dcell or Corecell. I also like high density PU foam for leash plug installs and rout-in fin installs so I can skip the fillet at the base. I’m just looking to skip the gluing process and the minor complication of finishing around the seams.
I’m working off the conclusion the fin guys have conveyed that finbox failures occur more often due to the weakness and mushiness of the liteweight foam around the box rather than the box or glassing itself, so I run that support from bottom to deck. Isolates the EPS core a little better from water instrusion arounf the box install and offsets the cancer issue on the deck, too.
My plan was to pour it directly into the cavity prior to shaping. That’s why I’m asking about the potential pitfalls.
We sell a 1:1 ratio pour foam that would work for this application. However, it might be easier to just cut out pieces of polyurethane foam from a surfboard blank and install those or you could use an already expanded high density foam like corecell or divinycel. Here’s links to both:
They pour foam expands so fast and hot and you’d have to pour such small amounts into pre-made moulds that it wouldn’t be worth the trouble. We’d suggest using Futures fin boxes or the new FCS 2 on EPS boards since they are glassed in and maybe go with a higher density blank to begin with…like a 2lb. You can also use carbon to to reinforce the fin boxes too which is easier to work with and costs less. Hope this helps.