Q-Cel reduce finbox meltdown?

Hey all,

I’ve got an eps blank that I’ll glass with epoxy. The horror stories of finbox meltdown have got me worried. I was thinking that something like Q-Cel might reduce the heat build up. As a filler it reduces the quantity of resin around the box, as a glass it’s not a good conductor of heat, and since it’s spherical you can put in a decent amount without stiffening the mix too much.

I checked the manufacturer’s website. Here’s a quote (my highlight): [indent]

Q-CEL® hollow spheres and SPHERICEL® hollow spheres products offer formulators flexibility in polymer composites. The addition of hollow spheres to fiberglass reinforced plastics (FRP), epoxy, compounds, and urethane castings can provide weight reduction cost savings and improved impact resistance. Insulating features of hollow spheres also work to the chemists’ advantage in thermal shock and heat transfer areas.”[/indent]

Sound like it might help. Has anybody tried this?


the trick there, is to use fin boxes that dont have excess pooling resin

like futures or fcs

use a slow hardener

and a micro fibre not a micro balloon

presealing the holes will help

also high density inserts as just released by fcs would make a big difference in strentgh as well

g’day Ryan !

…this might be just me ,

but i use q-cell to fix dings here.

i use milled fibre to insert boxes and plugs .

i have not however used eps blanks yet ,

so i don’t know if the same ‘rules’ apply ?

…but , i hope this helps , anyway ?



edit :

i did do a couple of fcs installs with q-cell and polyester resin a few years ago , come to think of it , and my experience was that the q-cell became very hot , and cracked a bit around the edges of the plug…

Hey Ryan,

those inserts Silly is talking about makes a HUGE difference installing FCS with quick epoxy.

Plus you don’t have to cut the fin plug hole to the deck anymore, just do it like the center plug.

Super strong.


I’ve done three boards using 2 pound EPS. I have used both milled fiber and resin filler (q-cell). I have installed FCS ,ProBox and Fins Unlimited 10.5 channel with no melt down problems. The real trick is to keep down the heat. Using what I learned on Swaylocks I did the boxes in two steps. 1/2 fill at a time. I also used a wet rag to cool the area while the resin kicked off. My 3 oz cup of epoxy resin that sat unused on the workbench started smoking and I burnt my finger when I tried to pick it up to move it outside. I recomend keeping a bucket of water near the work area just in case.

Eh? I must be out of the loop- what are these inserts? Can you show me a pic, or a link? Thanks -Carl


I didn’t expect to uncover so many good tips on the topic.

Except for Silly and his bad poly experience, sounds like Q-Cel and epoxy for center fins can be done safely with some precaution like Stingray used.

I’m still curious. Are there high density inserts for center fins? Stingray, did you have a really tight gap between the opening and the center fin box?

hi again Ryan !

just what boxes [?plugs, too?] will you be using with your eps blank , exactly ?

when i mentioned the cracking q-cell, it was with F.C.S. PLUGS , only. And using polyester resin , with a polyurethane blank.

i have NEVER used q cell in a box [ for eg: installing a bahne / fins unlimited type finbox]

were you thinking of doing fcs side plugs , with a back finbox ?

What board will you be making ?

… one with 1, 2, 3, ?4? , ?5? fin options , by any chance ? [you KNOW i like options eh , with fins , in my boards ?!]

 cheers mate !


Hi Carl,

I saw the inserts in a thread that Drewtang had posted in. Asked the local FCS rep and he knew nothing about them, maybe a U.S thing, but they look like the go for low density EPS.


Same gap around the center fin box as you would see on a regular longboard in a surf shop. About 1/16 all the way around. I had the least amount of heat build up with the fin box. I think the problem with FCS install is you have so much resin in a big pool that the chemical reaction makes lots of heat. Some one posted boards with the FCS foam inserts a few weeks ago. Did you try Foamez.com or check out the FCS wab page?

One day I went to a large glassing shop and asked if they would sell me some milled fiber. The workers were on their break. They all just looked at me as if I was speaking Greek. So I explained what I was doing and one of the guys walked into the shop and came back with a bag filled with powder. It appears to be ground up fiberglass and it works awesome.

If anybody knows where I can buy this stuff please post. I do have a friend who make his own using an old coffe grinder!

You most likely won’t have issues with the local temps down so much. As for

myself I would never do epoxy wet work in lower than 80F, and I would never

install hardware in one batch at 80F (if that makes sense, just my personal

findings…). Seems like a lot on this site have settled on 65F

Be sure to have at least a wet rag or even a bag of crushed ice handy if you

are potting hardware, esp if the epoxy has larger volumes or ragged holes.

The inserts are similar in shape to the stickers they put on the deck (not the

inked part) and are about 3/4 inch deep made out of higher density EPS (they

claim 8 lb/cu ft). They have a bearing-guided bit and flat plate capture jig

much like Future installs.

Hole is milled in finished shape, insert installed with epoxy, then the board is

glassed as normal, finally hardware is potted. Inserts for rail-only.

Airbrushing over flushed inserts is okay, and the ring-shaped hole to the deck

is not necessary. Just make the hole like the center plug holes.

q cel is used as a sandable bog

and has no real strength

even balsa dust is fine fibre

or micro fibre which is sold in a bag as a glue powder for mixing with epoxy

its very cheap and available at any marine shop

i have a pot life of 35 to 40 mins on my resin and never had a problem with exotherm

i do however preseal the hole first and allow it kick

but im an experimental board builder and have been using high density inserts right from the beggining.

fcs releasing the product, has confirmed for me that it is necessary for a strong install in 2pd eps

wouldnt be neccesary for boxes

but i dont like boxes so ill stick with the inserts and slow cure resin

fcs provide a bag of fibre when you buy manufacturers sets.

i never had to have water or ice

just make sure the whole is drilled as per manufactures instruction

ie. no more than 2mm deeper than the plug

a lot of this guff i learned form Plusone btw

I’ve been consulted by a few board makers who have had hardware installs melt

the EPS foam core. I’ve seen them, some were as large as a hand print, just

hollow around the plug.

I’ve reduced issues to the point of not happening. I’ve seen two shops in my area

that had full sets of boards (like 6 at a time) have meltdowns. The guy was just

about to cry, as they were customer boards. Also, the epoxy exotherm varies a lot

with the brand and speed of the hardener and especially with the ambient temp.

Experiences will certainly vary but I wouldn’t call the issue of meltdowns bullshit,

definitely take the warnings seriously when we have warmer weather again.

Good Luck.

This is working out great. Lots of good stuff on an issue that can really ruin your day.

My main concern started when thinking about about a single fin center box. I wasn’t sure if any particular system was more prone to meltdown, I was just looking to avoid it whatever I use. I was talking to a buddy and I thought about using microspheres (Q-Cel) because they have insulating properties and filler cuts the resin volume.

To answer your question Chip, after the new year I’m going to build a wide-ish 7’-6". Doing parallel singles with sidebites for versatility. I guess that makes it some sort of odd quad. It’ll be my first board. Up to now I’ve only done dings, delams, broken boards, and a skimboard. For some reason I’m set on an unorthodox fin set-up and shape. I’m calling them parallel singles. The idea is all Thrailkill and I can’t remember what name he uses for the set-up. I was inspired when I got to hear him describe it at the Cerritos forum.

I’m just throwing the side fins in for entertainment. I’ll probably use Futures. They look good and stout with lots of fin options. Plus I’ve watched a few be installed so that makes me a little more comfortable with them.

Just in the planning stages right now. I’m slow as a snail, but I’ll get there. Got a little obcessive/compulsive thing going so I over analyze things way in advance. Hopefully this topic is helping people that are trying to do something right now.

Thanks to everyone for all the advice.

I have found a simple solution that I think works well.

Use a slower reacting epoxy to set your boxes. I just did this one here, EPS, and I routered the foam all the way to the glass on the other side. Took a good amount of epoxy to fill the center longboard fin box and the FCS plugs.

I used System Three General Purpose with the slow hardener. Now I will probably go a notch faster next time, as this took 24 hours to get rubbery enough to pull the jigs, and several days to be hard. BUT no excessive heat was produced.

I only filled the boxes most of the way with it, when it gelled, I used the laminating epoxy (RR) to fill the last little bit around the edges. It’s got UV inhibiting properties that the other stuff doesn’t … I didn’t want the System Three exposed on the surface.

Just get a pint or so if you’re only doing a few boards.

OR, do this: cut your holes, then mark how deep the fin box goes in. Mix epoxy and fill to just below the mark. When it gels good, put the box in and pour the rest.

Also you can put the epoxy components in the fridge before mixing. It’s fin boxes so no big deal if it’s thickened up a little … you’re not wetting out fabric with it.

OR, if you live where I do, set the board outside in the snowbank =)) THAT will put the brakes on 'er …


Howzit stingray, I know Fiberglass Hi carries milled fibers and most likely any other materials company would too. You can make your own by cutting up some glass strands. Boat material sellers probably have it also.Aloha,Kokua

Too much resin = too much heat. Make your insert holes in the blank as tight fitting as you can (and still get the resin in).

Aside: the surface area of the hole you mill is what determines the strength of the install. It’s only at the interface that stress transfer happens, so more “glue” does not make a stronger install, except that a bigger insert hole means a larger contact area but the larger hole means more resin which makes it more likely to melt the blank.

Using Qcell, milled fibers, and the like, mean that there’s less resin by the volume of the “other stuff” you use, so addition may help reduce the likelihood of a meltdown, but will not mean a stronger install. Thickeners are useful to make the resin lighter, pasty and maybe more workable, but they don’t, generally, add strength.

Howzit Honolulu, I am a poly guy through and through and only use a little white pigment and milled fibers for plugs and fin box install mixtures. Aloha,Kokua

fiber makes stronger

balloons dont

also just want to add that fcs state the oversize hole

contributes to the strength of the plug

the ends of the plug are only 1mm thick

not very strong unless u add some fibre reinforced glue there

dont know why they just dont make the plug bigger?

"Howzit stingray, I know Fiberglass Hi carries milled fibers and most likely any other materials company would too. You can make your own by cutting up some glass strands. Boat material sellers probably have it also.Aloha,Kokua "

Hello Kokua , Hello Swaylock’s

I am using miled fiberglass because good people like Kokua have recomended it. Very strong and easy to use. I am willing to pay for this product. So far it’s been free. Good luck I guess !!!

Fiberglass Hi. oh yes , why didn’t I think about that ?

Share the stoke!