fin box install issue

g’day everyone - i’m a backyarder and this is my first foam board. I’d made a couple of HWS previous and also fixed acouple of snapped foam boards. But this is my first attempt at shaping foam.

I was lucky enough to borrow a Wayne Lynch Evolution 6’3" from a mate and have attempted to replicate it with a slight increase in overall volume. I also had a snapped fun board that i stripped the glass off and for each step of the shaping and glassing process i have had a 4’6" board to practice on which will be for my son.

I did a glass on fin for the little board but i wanted to do a 2 + 1 for the 6’4". I followed Stingrays thread from a few years ago so after the fill coat and before gloss i have cut the stringer and foam and glassed in the fin box no issues (maybe a little wonky!!) however when i came to sand/grind down the resin and remaining box that was sitting slightly proud of the board i have generated a slight hairline crack on one side of the box between the box and the resin. The question is should i remove the box and start again? can i glass over the box and “seal the deal” ( that may minimise water ingress but would not neccessarily do anything for the structural integrity of the box install)

At this stage if i do redo the box can anyone give me some tips on the process.

thanks in advance



Hi Noodle, I bought a new computer. I’m totally lost because it’s Windows 8 and I’m not tech savy…and most Tech people go so fast I just tune out…so no photos from me 'til I sort out all this computer stuff.

I think you have two options…paint some resin into the crack or “cap the boxes”. ( with 2 ounce or 4 ounce cloth) … I have a small wood sanding block,about 3 inches long, 1.5 inches wide and 3/4 thick. If it was my surfboard I would sand the FCS plugs and the center box with my little sanding block. Don’t dig a hole. Use long strokes to make it all flat…and then go from there…In the back yard it’s not a big deal to add some resin around the boxes…I do it all the time…or do a whole lot more work and cap the boxes.

.Today I’m doing a repair on a Firewire surfboard…There’s crack along one of the Future’s side boxes. I guess we could blame the sander for sanding too much. Or blame the glasser for glassing so thin or blame the designer for making the board so light… No blame game here. I’ll add a small patch of glass and resin…Stingray


If you don’t mind a slightly crooked fin,

Next time,

Sand sides of the box really rough.

It keeps this from happening.

Sometime just the heat of the resin will cause this.

So will heating up the box during the grinding down process.

Sand board,

Mix some clear resin with some styrene to thin it out.

If no styrene, heat it up.

Paint over crack, and let it seep in.

If you put a fin in the box during the resin painting, it will re-connect the side of the box.

And yes, you can glass over the box.

That may keep this from happening again.

Stingray, fixed a Firewire longbox that came through the deck too.

Quess that stringerless thing does have its downfalls.

Thanks Ray and Barry for the comments

Given its my first and i have now learnt a few lessons i think i might just finish this one off and have an excuse to have another crack at another one.

so best option is to sand down and get both fin box and FCS plugs all flush, then thin out resin and paint in and try and get as much into that crack as possible - whilst painting insert the fin into the box to try and assist adhesion. then for good measure glass over the top with 4 ounce cloth - should that glass overlay be patches or am i better off doing the full tail area??

thanks in advance guys


If were my board I would put a patch of 6oz. Glass over the entire box. Then cut out the box Chanel when the resin is half kicked. Then hotcoat twice as if it were ding repair. No need to remove entire box unless the fin is crooked. If you want to remove the whole box let me know and i’ll try to coach you through because you have a couple ways you could go about it.

Def cap the box with cloth. It may otherwise leak.   When you do, fill the box with gelatin from the grocery to keep resin from dripping in. Either cut out the cloth over the box with a razor before it completely cures or drill a hole and route it.  It is a good idea to put a old fin in the box when you first set it so you can avoid misalignment. 

if you do need to take out the old box you will need a beefy router, safety glasses, a steady hand and half a day to kill  ( go slow, avoid killing yourself). Build a 1/4 ply router template to make a clean job of it. 

all the best