I have just done my fin box instal ( fu 10.5 box ) and all looks good. I installed this **after **the hot coat,beforesanding. Im just about to grind down the box and I would like to add a patch of glass over the lip of the box to give the area strength, so my question is -
**Q **- Would it be best to sand the entire hotcoat as usual, then tape of my desired shape of patch over the box, sand that area down to the weave, then Lam on the cloth, wait , then hotcoat same area, wait, cut cloth and hole slot, wait till cured, then fair edges and move straight to the Gloss coat??
OR - is it best to do this **before **I sand down the entire hotcoat? Or does it not matter at all? I thought it may be better to sand board out first as this would allow for a more even patch area…
If anyone with experience could lay out the steps in layman’s terms it would be most appreciated . Thanks so much for your time.
If you used surfacing agent in the hot coat you need to sand to get the wax off. I would sand, then fill the slot tightly with some spare foam, then laminate. Rout it after finish coat with a trim bit. It will be well over built.
i just did one of these following some tips i found on here.
Before hot coat route and drop in box. then take router and a few pieces of wood to make your router sit higher than the flange on box. Set router bit so it is slightly above the glass on the bottom on board and router flange mostly off, then just a light touch up is needed with sander to make flush with botttom lamination. from there tape off and add your cap to the box. let it set up feather it out, hot coat and go!
whoops just realized i misread and you said AFTER hot coat
On a single fin box you really don’t need to put a layer of glass over it.
For installs, I like to put glass in the routed hole and then mix saw dust in with the resin to thicken it. It seems to make a strong install. The one “trick” I know is that I route the box 1/8" wider than the box and I have some popcicle sticks that are 1/16". So I break a stick into 4 parts and use that to align the box while I press it in - keeps everything straight. Then once it is all clamped in I take the sticks out and fill in the holes.
Since you already did the hot coat, here’s what I’d do.
Sand the board as you would normally on any hot coat, bringing the box down flush to the glass. Put a piece of 3/4" masking tape over the slot in the fin box. Lam your patch over the box. As soon as the resin gels sufficiently, take a clean straight edge and a razor/exacto knife and cut the glass around the edge of the tape. Remove that glass and the tape. Put another piece of 1/2" tape over the slot once the lam resin has fully kicked, then hotcoat again. Avoid getting too much resin on that tape. Remove tape when hot coat gels. Sand accordingly.
Don’t forget to blow the sanding dust out of the box and make sure the face of the box is dust free before applying tape. Tape must adhere well to prevent seepage.
My fin box in my 9’7" HWS was seeping salt from between box and epoxy surrounding it after a decade of use, and also appeared to just be starting from between wood and epoxy when I drydocked it for reinforcement.
The fin box was originally routed into a 3/4" wide chunk of cedar on either side of the center 1/4 inch stringer that mates to the deck, so it was very solid to begin with.
I went a bit overboard on its reinforcement:
I laid CF roving in those grooves next to box, sanded flush, then glassed over with some 7.5oz which remains a bit too visible.
5.5 years since that reinforcement and many many miles ridden since.
Solid.
I had built a fin for that stretched box, and afterwards I did have to sand the base a little bit so it would fit tightly. I feel the Fin should mate with as much surface area inside the box tightly, rather than wobble even slightly and exert pressure on a few areas of the box only. Getting the fin to fit is easy, getting it to be a honeymoon fit is a challenge, especially when the box is older, worn and stretched.
I cap all the finboxes with double 4oz on the boards I glass.
Hotcoat 2. Route and drop in finbox like you normally would 3. Grind box flat and the area around it (make sure the box and seem are slightly low) 4. Cap with two layers of 4 oz. No need to tape off, just be gentle and the resin won’t drip into the slot. 5. Hotcoat the 4oz and surrounding area. 6. Sand board normally 7. Gloss and Polish if the board gets that finish. 8. Route out like in this video. https://www.youtube.com/watch?v=oS7hB_n0kfA . You can sand the whole board then cap/sand or you can sand the area like I discribed, your choice, doesn’t matter