Different finbox replacement (FCS Fusion install ?'s)

Hello, i have routed out the old finbox of my epoxyboard, but the old finbox is from an other shape then the new FCS fusion.
Its an kiteboard from naish with its own patented finboxes. So the problem is that the old finbox is deeper in the foam then i need for the fusions.
I routed out 16mm and the fusion box will fit very well, but unterneath it will be still some plastic of the old box.
Will i get a good bond with the board in this case? Or is it better to route out all of the old box and build up the hole again to the 16mm for the new once?

I’d be tempted to try it as-is, maybe with a layer of cloth and epoxy resin in the hole. Then cap the new box afterwards.
Is the surrounding foam EPS or Divinycell or ???

Thank you. But now i routed it out some deeper. I dont know if the core is eps. It is only a little bit harder than styropor. I have allready put the fusionbox in an everything was fine with the resin. Now i have to grind it down and then glas it over. Some tips for this?


I thought that grinding happens after glassing with these pre-glass plugs, similar to a leash plug. Sink the screws, stickers over the holes, add the patches. I like to cut a slit into the glass over the top of the holes so there are no air bubble or tenting of the cloth over the plastic lip )that eventually get ground away.

Maybe someone who does these day in and out can comment.

Ok i will try this. As you can see the board is white. When is the right time for the paintjob, before or after glassing?

I defer to Resinhead in these matters. He told me graphics will ‘pop’ more if applied after glassing and first fill coat, sometimes the cloth and resin make things a little hazy. I have yet to repair one like that but I have one coming up that will need white paint after foam and fiber are repaired (windsurf board).

I have done the paintjob with a waterbased acryl from Belton. Hopefully the glas will get in a good bond with it. So far i am very happy with the repair. I think im my case it was better to paint now, because it dosen have to pop, it only had to match the color of the board. I think the best solution is to put pigments into the resin to match the color, but i dont have them. I also have an other repair to do after this one. Same finbox like here (i am goofy ;-), but its a bamboo finished board.

I added 2 layers of glas. Next step is to blend the edges and hotcoat. I dont know if its better to grind down and open the finbox before or after the hotcoat.

The grinded down box. I have to do some more grinding and then hotcoat. I have no surfaceing agent, Any tips for the hotcoat without it?

It looks like you are making progress with the repair.

Polyester (catalyzed with a small percent MEKP) resin or epoxy resin (parts A resin plus part B hardener)?

Not knowing which exact foam is in the board I would have used epoxy. One could have tested a small piece of foam with acetone to make sure it is not EPS as acetone melts EPS or ‘styro’ type foam.

You do not always ‘need’ a surfacing agent with epoxy, although with Resin Research people use Additive F with good results. I have added a couple drops of denatured alcohol or xylene at times to get a little more ‘flow’ out of the epoxy but prefer not having to. Warm resin, warm shop, freshly sanded surface, no finger prints, etc. to avoid gaps or ‘fish-eyes’.

Polyester ‘lam’ resin needs the wax surfacing agent to create a barrier to the air, this allows the resin to fully cure at the surface. Polyester ‘gloss’ resin often has the agent already in the can.

When things go wrong with the wax surfacing agent people often try to put wax paper over the sticky parts to get it to cure more. I have heard that one can spray PVA mold release on poly lam resin to create a barrier too but I have never tried that.

You are headed in the right direction and doing fine. Repair looks good. These boards are similar in construction to Surftech and Boardworks. EPS core, Propriatory vagum bagged layup and the the shell is painted and clear coated automotive style.

Thank you for your good tips jrandy i really appreciate it. Yes i work with an epoxy resin and i think its also an eps core. I have found the additive for epoxy. I will order it next time with the missed pigments. @McDing yes you are right the board looks like its machine finished, because the hotcoat is very thin. My next question is what i have to use when polishing the hotcoat?
I want to have it shiny again. The 600 grid with water cant do that.

I use a sanding polish from a panelbeater store with a wool pad. It takes out fine scratches and brings epoxy up to a shine (not quite a gloss, though)

Thank you red_boards i will try to get the final shine with a polishing maschine. I have started the second finbox of the other board. It was a good idea to cover the bottom of the jig with cork because now it dosent move any more.
Please take a look at the rails, they are painted in silver over the hotcoat. What kind of color i have to use for something like this?

The resin is not completly dry after 2 days. Try to add some heat but it dosent work.
How could that be?
Could i have added to much microbaloons?

Can i use a acrylic paint on the epoxy resin?
I think with a hotcoat over it works well.

I routed it out new, because it wont get completly dry. Fingernails leave a mark even after 4 days. I think the mixing of the resin was not accurate enough.
I have made a fin template to tape it down better than with a normal fin after instaling the new box.
The last time the box came up a little bit during the drying process. When pressing it down the resin comes up again. I hope i can avoid this now with some tape over the template to hold it down.
More tips are very appreciated.

I got a new problem. I build a angle measurement tool and find out that the old finbox is not in 5° like the fusionbox I want to replace.
The finbox on the other side has a angle of 7°. I know that there will be no fcs solution for this.
Is it possible to tilt the box 2° to match the old fin? What would you suggest?

I added ‘fusion’ to the title so people know what type of box you are using.

As far as the resin not getting hard, that is usually a ratio or mixing issue. Epoxy needs the correct amount of each part mixed together well to react fully.
I prefer a small scale (by weight) or syringes (by volume) for small batches. For example RR Kwik Kick is 100 parts resin to 45 parts hardener by weight OR 2 parts resin to 1 part hardener by volume. One cannot mix units weight and volume, they need to match for each side. Also remember to zero (tare) the container when weighing.

To add one more degree turned out to be ok. Now i am working with a better scale  and the epoxy gets hard the right way. My problem was a  ratio issue. 

Is it absolutely necessary to add one or two layers of glas over the box or is it enough to fix the paint with a thin layer of resin?