EPS / Epoxy... Finbox install meltdown

It was very hot the day I installed the ProBoxes into the latest board. 100 degrees F in my workshop. I did a sloppy job putting some 4 oz cloth into the routed hole before installing the boxes. My brain is thinking poly and I only have fast hardener. Normally after pouring the resin I babysit the project with a wet rag to keep every thing cool. For some reason this time I just walked away. After power sanding I can see that I melted the foam around the boxes. It’s a gift for a friend so I explain what happened and warn him about water getting into EPS foam. One week later my friend returns the board. His ass landed on the fin and busted out the box. It’s my fault for doing a crappy install…

I done this type of repair many times before. All polyurathane blanks. Never EPS…So I cut out the area and make a replacement block of foam…Mix up some Epoxy…add some resin filler and shove the bolck of foam into the hole…Well…I did a crappy job shaping the block of foam…and I’m still thinking poly…I mix up some more epoxy to pour into the gaps…Wrong…now I’m getting major heat. I got a wet rag and tried to cool everything down but it was too late.

I came back the next day to a big mess and had to dig out a whole bunch of melted foam. Sorry no photo.


My new plan is to cut out around the hole and lam two layers of glass around the inside to isolate everything before I glue in a new block of foam.

All comments welcome.

If you are in north San Diego county and you have a White Probox side box please contact me via PM



I think this has happened to all of us at one time or another.

What density was the eps?? and what brand of blank if not self made?

Do you have the latest probox router bit?

is it adjusted possibly too deep?

This happened to me with an FCS install 3 yrs ago with 3lb foam!!

my suggestion would be to make sure you have the new router bit with the depth tweaked perfectly to eliminate excess pooling.

use long cure epoxy,it seems to get to a less dramatic exothermic peak. If you don’t have long working time hardener you can put your resin cup when giving it your 100 stirs and submersing the cup in a ice water bath during your mixing.

Also consider a waterproof epoxy paste doing approximately half your box and filling the remainder with resin when the paste is starting to harden. Also you could take that same paste and lightly coat the sides and bottom of the routed hole, wait 15 minutes and install as usual.

I have heard of others adding "stuff "(fillers) the the resin to help minimize the exothermic results. I have never done this.

I am pretty sure some of these ideas will not be supported by the pro box manufacturers.

Chalk one up for experience!!

high density inserts

if you cant get any h d foam

get some P U offcuts

e p s no good for instalations

darker than dark


Resin Research with fast hardener ,Industrial grade 2# EPS / homemade blank. Latest/greatest ProBox install router bit.

I’m taking full blame for the exotherm / meltdown. Not placing blame on RR or PB

Thank you for your input. Moving forward I need to make sure this never happens to me again. I will be buying some slow hardener in the future. Might have to start doing half fills like you say.

what are you crazy darkerside

that would take like , 8 minutes

cant have that

looks like poor old ray has been feed a bit of bad advice

but thats probly how they do it at s t

darker than dark

stingray what you do is use an infusion type of resin

very slow to go and doesnt get hot

it doesnt really get a full cure for a few days tho

it does astound me however the continuing bad advice wrt to fin systems in eps

the box should be isolated from the core for other reasons besides water leaks,

protects from exotherm and greatly increases strength

High density inserts are the best solution for a longlasting and durable eps surfboard

i personally wouldnt use eps any more, without some sort of sandwhich skin or many layers of glass vaccumed bagged on (as in COIL)

there is no point really

polyurethane foam (with polyester or epoxy) is perfectly useful for a simple cheap board

at least it wont suck water

ResinX works great and never melts EPS, as it has very low exotherm. Someone around you might have some. Matt could tell you who. Why flail with inserts, dual batches, wet rags, etc? Just one shot w/ResinX. You can sand the Fast in 2 hours. I now install all my Bahne boxes and most of my leash cups with it, besides glassing lots of complete boards with it. It is the straightest line to where you want to end up for a lot of EPS projects.

It takes guts to post up a disaster like that, but it will help others to learn. Paul’s right, HD inserts are the safest way to go

for after-glass installs in EPS. And if you bust one, water’s not into your core.

I use ResinX for ProBox and centerbox installs in EPS as well, 1# and 2# densities. Very little exotherm and no melting at all.

Little trick I do to reduce grinding work on the boxes and resin it to cut the gelled ResinX with a razorblade flush with the bottom glass. It cuts real easy before it totally cures and makes grinding the box down quicker because you’re not heating up the resin wall with friction…in my experience at least.



Just throwing this out there - as newbie myself I had to melt some eps doing FCS. I now take a sandwich baggie with frozen peas ( don’t tell my girl or we are toast) and tape it to the underside of each rail fin. I find the center fin doesn’t heat up as bad. I don’t cut through to the deck on that one - letting the stringer be it’s strong base. But the side fins need that collumn of resin to attach to the deck inside - thus needing a lot of resin. I get no melting at all - or bubbles cause the cold makes it suck inward on the resin. This way no need four kinds of resin or inserts or lots of work. I found this trick in the archives and thank all swaylocks braddahs for posting.

Hi Stingray, I agree with Mike D. It takes a lot of guts to post when something goes wrong. Everyone always loves to say, “Look what I did!”, when it looks good but when something goes wrong is when we all need the most help.

I have replaced large sections of EPS and Resin-X and it seems to work better even if the board is made of epoxy (the repair looks worse with epoxy than resin-X). It does have an exotherm but nothing like epoxy. If you want some you can reach me at this # 248-830-4122. Your repairs will go so much faster in this process because now you have more to do. With fast resin-X you may be able to fix this in a very short time. Long term, resin-X will not yellow around the fin box like epoxy has a history of doing before the rest of the board. Under most conditions with fast resin-X you can do repairs like this in half hour incriments. If you make a lot of eps boards and you use epoxy to put in your boxes, you are really missing out. Both in time and money.

Best of luck


Just a quick note that hasn’t been mentioned yet:

when putting in your high density inserts, or replacing eps, it’s not necessary to use epoxy at all. A polyurethane glue (I use gorilla glue) will do the trick just as well, and has no exotherm. It will, however, be brown. But I always go for function and weight savings when doing repairs on eps boards. Install boxes as usual afterwards.

I agree that isolating the core from the fin boxes is a very good idea. I got a water soaked stringer from a ding I didn’t notice right away on an eps longboard.


Heat Kills !!!


Keep a bucket of watersoaked rags around.Apply them(as the boxes start to get overly warm during set-off) over/under and around the boxes with a fan on them = no meltdowns.


Some interesting discussion so far ,let’s keep it going and keep it positive…

The fact that I had a melt down during the original Install is due to Me not following the ProBox instructions. I used 4 oz cloth and did a sloppy job and it was 100 degrees in my workshop…I’m actually quite good at installing boxes for a backyarder. Shit happens!

What has me mad is the fact that when I went to repair the board I had a second meltdown. Now I have a major hole that needs the foam replaced. It’s all the way to the deck now…Aprox 2 x 6 x 1.5 inches.

I’m looking for advise on how to get this hole filled with out a third meltdown. (Low dollar solution)

Ok… gorilla glue if I have to…

I’m not buying any Infusion resin or any ResinX any time in the near future. Thanks for the suggestions…

How much does a quart of Resin X cost??? With hardener?

Fun small waves at Igor’s this evening…

Go surfing


Hey S-ray,

I looked at my notes on my melt down and my theory for my problem might fit your case too.

I mixed up my fast cure epoxy and added my filler that came with the FCS.

poured all three sets, but the set that melted down was the last one I poured.

My theory was that after each pour the main batch of epoxy was getting to a “critical exothermic mass”. By the time I poured the last plug the epoxy batch was well on its way to max exothermic reaction where the other two boxes did not get the increase temp help from the main batch as much.

Also there was a previous thread where randy rarrick took a surftech egg or rocket model surfboard and added 4 probox fins to it. I mocked it and called it barnyard if I recall. But then probox larry posted some pics on the master that did the install. I don’t remember who it was but the pictorial and job was expert top notch. That person had some friggin epoxy skills.

On compsands where you skin over the inserts it is very easy to do. On painted foam or solid resin colors its a bit harder to make look good. On clear glass and white foam it is the hardest to get a nice looking and functional foam insert. We only put inserts in 1 lb foam and under with a rare bring back for a box problem. My personal preference is pre glass systems. But you got to put in what the customer requests, so knowing all the systems is important.

I hope you figure it out and don’t feel like you need to put inserts in 2lb foam.

talk to you all in a month or so.

hi mate, i believe i would fix the board by using a old piece of pu foam offcut and glassing it into the prepared hole. sand it flat then glassover the top with 2-3 layers… install the new box then sand the whole lot… finish coat it and walla your strong without a fin wrong…

ray listen to dave he has hit the nail right on the head

this is an easy fix thers nothin more to say realy

darker than dark

Just think of it this way…

…Probably rides better.