Longboard Finbox Lam vs Hot Coat Install

Tried the lam approach. Router left black marks all around the box, didn’t make a clean cut (exposing glass white glass threads, and had to estimate amount of lip exposed for the hot coat (had to grind down and went into the foam in one part).

Routing on the hot coat gives you a real clean line, easy to sand router marks, and a perfect level lip on the board.

Looks like I’m routing on the hot coat from now on.

many mahalos,


I agree with you… routing on the hot coat is way much more cleaner… I don’t know why, but I also feel that the router cuts better and faster on the hotcoat…


here’s a few follow up issues when routing into the hotcoat.

How much space are you allowing the box ro flaot in. I’ve seen as much as 1/8 on all sides, and as little as a few millimiters.

Also, how much of the finbox do you leave exposed. Given the natural rocker of the tail section the box will never lie flat, so do you measure for the ends to be flush and then sand down the middle?

I used to rout prior to laminating, but that always made such a damn mess. I am now a convert to this method as well.


Hey drew… I personally like to leave around 1/16’’ space all around the fin box… and try to level the box evenly leveled as possible to the tails glass surface also trying to leave exposed out the least of the box… just enough to be evenly sanded…



what up…

So are you laying any glass in the bottom of the slot? I lay a couple layers of 7oz and then fill with a lam mix of cabosil or micro balloons.

what do you use lam it in?


I rout the box slot as close to the box size as possible, then I use sandpaper to sand down the sides so the box slips in. I then try to keep the middle of the box flush with the bottom of the board, which the leaves the ends high. After everything is set I line the box slot with cloth, wet it and then put the box in. After everything cures I then sand the ends of the box down.


Yes drew… I lay two 6oz layers of glass on the bottom of the slot… and before putting the box in I add a bit of resin to wet the glass, put the box, and fill it with resin mix (lam resin, white pigment, and chopped or powdered fiberglass, and of course catalyst)…



Do you routinely rout into the hotcoat? If I remember correctly, you routed into foam on the board that you helped me with.

Have have you changed your method since then?

By the way, I just finished shaping my second board (actually, it’s the first board I shaped 100% on my own). I’m waiting for the order from Fiberglass Hawaii to come in so I can glass it.

It’s for my dad. Hopefully he’ll be MEGA STOKED and actually paddle out next time he’s up.


yeah brother. I have changed my method. Once I get this method down, it will make for, hopefully, very pro looking installations.

Sweet about the new board for your pops. I gots to come check it.

You around this weekend?

I’ll be around this weekend.

If Amy and I ride our bikes to the beach tomorrow we’ll stop by on our way up.


WHY are y’all putting glass around the fin box (I’m assuming the standard old-time Fins Unlimited box)? No amount of glass there will make the box stronger in a useful manner. Strength is needed on the board’s bottom surface, at the front end of the box, so you don’t rip it out when that pinnacle MF rock sticks up farther than you thought.

The only purpose of any resin or glass around the box is to adhere it to the foam. The plastic of the box is more than strong enough.

Ergo, the cleanest install is the one which only just barely leaves enough room between foam and box, to wet out completely. Close fitting router work also ensures the box is straight in the board - a widely routed hole offers the chance the box will go in at some skew angle. This requires a closely and carefully made router template, securely (and of course temporarily) affixed to the board when it’s used.

Now if only I could take my own advice…

Aha, the trick for this type on installation is to cover the area with 2" masking tape, route through it,pull up the tape, intall the box with clear resin and cloth. The reason for this is, the fibers from the cloth spread out onto the lamination, bonding the cloth in the route to the bottom of the board. It is much stronger that the typical butt joint that a regular route and install has.

Jim, how much & what weight glass do you recommend for this method? (1 layer 6 oz enough?) Always love hearing a tip from you, never thought of the masking tape before routing but it makes sense of course…

PS I had someone suggest to me once that the white and black FU boxes differed in strength. Any truth to that in your experience?

I work closely with Fins Unlimited and they advise me to NOT use the white boxes (I haven’t broken one). For the glass in the route, you need to grind off the side alignment tabs, but I dry fit the box with as many layers of cloth that will fit without cramming in the box. I have glass shops installing my boxes with just micro-balloons and resin, but I personally feel that glass creates a barrier between the box and foam, just resin can get cracks through it. If you are going to hit something hard enough to rip out the box, nothing will help then.

Before there were any suitible small boxes, I made a set of polypro inserts, 1/4" thick, that were the same as my own fin bases, I would route the lam’d bottom, lay 12 layers of wetout cloth over the hole and press my inserts into the route. After gelling hard, hotcoat and a tap with a hammer and they would pull right out. I worked laying teak decks on yachts and all the marine fasteners are tapped into the glass hulls, so when I made these fins/boxes, I tapped the stainless screw right into the cured glass. It was good for me to be able to have a cheap way to do multiple boxes, that were lighweight, in team and experimental shapes. If the ride wasn’t the desired effect, route in another box, until you got it right!

Honolulu, If a box rips out, it takes everything with it, but for for water migration from small cracks, lining the route with glass stops 90 percent of this. The solely resin installed boxes, have the resin break up into small pieces when hit, allowing water to find it’s way to place you don’t want it to