Sealing EPS technique for microballoons/resin

Hello guys, i don’t want to start this debate between spackle/microbaloons i just have a few questions regarding the process itself as i can’t seem to find a good video about this stage.

So my EPS cutouts are low density 23kg/m3 so i get beads pulled out when shaping, i am very delicate but it still happens, mostly around the stringer where i use qcell/resin to glue the stringer and if there is overflow it goes in the bubble matrix and when i’m shaving it down the razor pulls big chunks.
I dont have those acrylic based spackles around as the FNF or 1time, i’ve used the most cheapest one i guess based on limestone? i’m not sure, funny enough i haven’t got any delams or anything, it works but it has a brownish color and it colors different than the foam.
There are also some vynil spackles i might try those, but i want to also try Microbaloonss/resin.

So far i understood that i have to mix 1 : 1 by volume (resin+hardener/ qcell) get a paste consistency and go, but here are the questions that come up.
When later sanding it does it sand harder than foam and thus resulting in low spots in the foam?
If after filling i go directly to glassing the bottom… i guess, doing a cutlap, will it color my lamination white? If i try to do resin tint? Also will it be a problem the board being upside down and having some beads filled on the deck and in the rail?

Or Sherwin Williams shrink-free spackle has been used to replace the now gray DAP.

Thank you for the leads, i actually sealed the bottom yesterday, and left it to dry with microballoons/resin i hope i dont get delams and i get a good bond :crossed_fingers: i will scratch it with 120grit before laminating

Stoneburner turned me onto micro holes/perf prior to “sealing.”
I mix up RR epoxy and then add microspheres until it almost gets crumbly.
So far been working well.
What I’ve been most stoked on is adding a bit-o-pigment to the sealer/putty. I’m a kook and like to lam with clear glue.
Plain water based spackle - makes for a nice messy dings.


I sealed both sides with qcells+resin, i believe my ratio was a bit too much on the resin side i had a hard time sanding it later, and kinda messed up my rail line but the resin tint i did later turned out great, adhesion was good no signs of delams.
Will post photos when it’s finished.

I also found this lightweight spackle and oh boy it is really light! I had no idea!
I will try it on my next build.

i still have enough eps 23kg/m3 for at least 10 boards but i feel like i made a mistake and should have bought a 27kg/m3, I’m thinking i should buy the denser one but what i’m gonna do with the one i have already?
I think i should try to go trough with it as fast as i can and just sell them cheap, so i can get better and have the new batch on a whole new level.
Currently my raw materials for construction cost around 150 euro with the consumables and i plan on selling them for 300 euro wich is close to what Decathlon is selling boards around here.

Not expert here but I would use that eps. From 23 to 27kg it’s not a big difference. There are branded eps boards made with 1.5lb (25kg). Just put another 4oz deck layer (or wood veneer or cork if you want).
And about the sealing slurry, the next time you can try with a 1 resin / 1 cabosil / 3 microbaloons megamix, and put a thin sealing coat, just to fill the surface. As reference, for a 6,0 board, 100ml of resin it’s enough.
Good luck.

thanks for the feedback!
I cant seem to find Cabosil around here, what would be the difference if i use 1 part resin/ 4 parts qcell?

Currently, i’m using fibreglass that is 163/m2 that is approx 4.9 oz/y2 so i get the normal pressure dings but nothing major so far, i try to keep the boards light, with this epoxy sealing i think it would be even better as while i was sanding it it was quite hard.

Qcell and cabosil are the same. You need microbaloons.

This is not the case… Qcell = “microbaoons” Soft, lite, easy to sand - good for filler/putty making. Cabosil makes for a thick, much harder, mix - good for reinforcing, but you wouldn’t want to make a filler putty with it…

Be careful with that water based stuff, as a ding through the glass will get mo’ messy.

Also, if making your own putty to fill with, out of epoxy and glass beads/Qcell/micro balloons (leave the Cabosil out), don’t worry so much about ratios as slowly adding beads until it gets nice and thick - just under too thick to spread (you may go to far, then have to add a little hit of glue) - then you shouldn’t have any problems sanding…

Excuse me. You are right. I’m not from USA niether from Europe, so I confused the names. For our friend, Q-cell it’s a branded name of glass microbaloons. Cabosil it’s fumed silica. Some stores sells it like Aerosil. I hope this helps.
Good luck

No worries janop.

Better safe than sorry!

That Cabosil can make for some hard, hard putty. I like a 50/50 Cabosil and glass bead/microballoon mix for harder edge putty on the tail rails, and sometimes for fin customization, but then more beads for easier sanding.

Good advice that mix for the rails edges. Thank you!!