I have been using FCS Fusion for a few years now and I am pretty happy with the ease of installation and Ive nverer had any blowouts.

I do have a question for those that might use them, or know of them…

When I go to sand the plugs down (after hotcoating) in beginning to sand the board, I am finding that I am exposing some of the cloth adjacent to the raised plug slots themselves. Those that know the Fusion plugs will know that they have a coloured rim around the plug slot, which is designed to be removed during the sanding process. So what Im finding is that I am sanding down to remove the coloured rim, while during this process I am starting to espose the weave of the my cloth immediately adjacent to the raised plug slots and the plugs themselves.

I am wondering if anyone has any suggestions of setting the depth of the box better so as I can remove the coloured rim, without exposing the weave. 

For the record my instal process is:

  • rout plug holes , set and cure plugs in

  • lay up 4 ounce cloth patches and have them cure before I laminate the bottom of the board.

To me it sounds like I am setting the plugs too low. Has anyone got any hints/tips on setting my router to a more apprpriate depth?


Cheers Marty

trying to avoid the same issue my process is:

-Route holes and set boxes


-Sand slots flush with the lamination

-Cap boxes with tape and hotcoat

-Final sanding

maybe a little more labor but cleaner results that way

Another trick would be to make relief cuts around the slots as the lamination is tacky.

p.s I use epoxy


I like to make sure the top of the box is as flush with the foam as possible. If you route too deep, you can easily “float” the boxes up to make sure it’s flush with the foam. When setting boxes (Fusion of FCS 2) I always look at eye-level to make sure the boxes are flush to the foam and the sand-away part is visibly sticking up. Nothing worse than boxes set too low. You end up hitting weave and creating disasters.

With Fusions, or any under-the-glass flange system, it’s important to not sand into the fiber around the edge of the box (where box meets foam bottom surface). Hitting a little weave around the fin slot opening isn’t a big deal, but out on the edge it’ll provide a weak spot to focus loads. The strength of the install depends on integrity of fiber over that flange.

When you install into complex bottom contours it’s always better to have part of the box a bit low rather than have a spot that sticks up and gets sanded through. It’s a good idea to keep box placement in mind when shaping so you don’t make a problem, and you can even adjust just a little to make sure there’s a flat plane for the install.

Good to hear from you Mike. I was was hoping you would see this and respond. Coil does an outstanding job of setting boxes properly and I remember you saying that you set them a very slight bit low and build up with a but more glass for max strength. 

All the best

Windswell has the right idea with relief cuts.  Just run a razor around those slots. I do it when the resin is still wet.  this has the advantage of being able to press down the remaining cloth tight to the box and push out any air bubbles.


for post lam?

Thanks for the comments guys ,really appreciating it!

Jamie…so your talking about the top of the box itself being flush with foam, not the top of the raised rims around the slots?

I have played around a little with installing at different depths however I always seem to expose cloth (cloth that has been fully wetted out, Im not hitting dry spots/air bubbles etc) as I keep sanding down to remove the coloured raised slot rims.

Thinking about what I have just typed, it seems to me that my boxes are to deep. Thinking about it more, the raised sections need to be as high as possible to ensure the least amount of sanding downto remove the coloured rims, but also need to be sure the top of the box itself isnt above the foam.

I tend to wet up and cure the football patches first, as this allows me really concentrate on getting the air bubbles out, one the patches are cured I then glass the bottom and concentrate on getting thebubbles out again…it seems easier that way instead of trying to wet out and chase out bubbles from two layers of cloth (i.e the patches and the bottom laminate cloth.).

Any others tips suggestions immensely appreciated!



I follow the manufacturers directions and have the outside edge of the box ever so slightly below the surface (1/32") and use a football shaped patch of 6oz.  Never had a problem.


FCS Fusion Installation DVD from FCS on Vimeo.


PS:  If the Original poster is having a problem with exposing cloth adjacent to the fin slots as he reports, logic would say if anything he is too high with his installation.  By setting the boxes lower in the foam you will only be nipping off the very top of the fin slots when you sand the bottom flat with a hard pad.  The higher up your box is the more material you have to remove from on top of the box to sand down to flush with the bottom of the board.

When installing post lam (before Hotcoat), I always set the depth so they lay a hair under the glass, then put 4oz patches on top of them, 1 per plug, then a full 4oz tail patch covering all of them. When I hotcoat, I make sure to be a little heavier where the plugs are to make sure it is leveled with the rest of the board. Then sand as usual. 


Hope this help,

Jean G.

Hey Mako

Thankyou… Youve opened my eyes… While i was thinking my instal was too low- thinking i needed to keep sanding down to remove the colour tabs, in actual fact my instal was too high- Therefore i actually needed to keep sanding down to get the tabs flush with the bottom of the board- all the while I was thinking it was just to remove the colour tabs… Not really thinking about what I was doing/or why… Def going to try sitting the boxes a bit lower… Ensuring the top of the box (not the raised slot rim)… Is slightly lower than the foam itself…


Use FCS Fusion a lot.

Found post lam valuable in setting.

And grinding, with a lam buffer down.

Understand, my work leans more to concave.

Plus with the cants that are used creates issues…

Use 5 deg and 9 deg boxes (with concave) always high towards the stringer.

Find using a die grinder with 40 grit effective.

And grind protrusions, clean up (tape up) and lam with 2 dog bones.

Then hot coat.

Anyone else???

Just wondering if the OP dealt with this problem? Was it a case of setting boxes too low or too high in the end? I notice the same on my last board, tiny bit of weave showing around the tabs

Hey Helter, yep seemed to get a better result now that I am setting them slightly lower, when I say slightly, I mean slightly! I think the instructions said something like so the box sits 1/32” below the foam… not sure How I could measure that, so Im having them sit a smidge, like 1mm below the foam, seems to yeaild a better result!!

Cool thanks for replying. I was worried I was fitting mine a bit too low, but I am definitely no more than 1/16th below foam. I am also fitting them post lam now, just seems a bit easier and more forgiving. Not sure if the pic below shows it clear enough, but if you look carefully you can see weave around the tab closest to the camera. Bloody annoying! Wish I knew how to avoid this, still a bit confused (As you were once!) whether its a case of setting boxes too deep or not deep enough. Will keep experimenting. I did get one board where this didn’t happen but I didn’t do anything differently so it seems a bit like luck to me (being a novice backyarder!) AS someone else said, it probably doesn’t matter much in the grand scheme of things, I just hate seeing anything like that, I don’t spend hours and hours and hours to see unsightly shit :smiley:

Actually this works better…

Hey Helter, yep that photo is exactly what ive been getting… i did a repair the other week where i routed out the busted box, did a foam insert and re routed plug the. Re set a new plug… i did this with the ‘slightly’ deeper setting that I wanted to try and it seems to come out much cleaner… have a couple of boards to do so going to go with the slightly deeper setting and see what happens!! Im hearin ya… very frustrating!! And a bbit co fusing as to whether your to high, or too low!!

Cool, good luck! I agree with others saying go deeper, you can always float it up a bit. Trouble is my first few boards were like WAFERS, at 1/32 below foam, there was about 1/16th of foam in the bottom of the box before the glass!! scary 5hit :smiley:

Helter, that looks like a small air bubble. Do you cut slits into the cloth to allow it to drape better over the proud parts of the fin box. There is a tendency for wetted cloth to ‘tent’ over a fin box as it is being pulled tight around the box? If I get bothered by one I open it up and fill it in with resin.

Saltbush, I think too deep is part of your trouble. I would try setting your router on practice pieces until you can get it spot on. If I got too deep I add cloth and resin in the holes to bring the boxes back up to flush with the surface. What are you using to sand open the boxes? Coarse grit hard flat pad?

Hey jrandy,
Yep hard pad, coarse grit to knock the boxes down!! Ok, give me an idea where in relation the surface of the foam (as in the bottom of the board) should the top of the fin box be sitting, not the top of the tabs… the top of the fin box itself!!?

Hi JR, thanks. I am not sure its an air bubble but it does look like it. There is no tenting. these were fitted post lam, with glass cut to size of socket, then a football patch over, all pulled nice and tight with fingers and squeegee. I suspect you’re right and may try setting them a bit shallower so they stick up more and i don’t go down so far when sending.
thanks again