fin install on wood board


So I’m building a hollow chambered board, 5’10x22’, not sure on thickness or wood yet. Its gonna have a big single fin, but I can’t find any information on how i should install the fin. box or no box?


It seems like you are asking the last question first regarding building a chambered board.  It is good that you are thinking ahead.  The easiest method would be to just glass the fin onto the board.  I suggest glassing the board and the fin with epoxy.  It can be done, but it is hard get poly to bond well with wood.  The advantage of Poly, however, is that you can make a gin clear glossy finish -- if you know how.  Make sure that you don't have any big chambers under the spot where you will be placing the fin.

Check out this thread:

It is a classic, and was what got me going on my chambered board build.

The shaping 101 CD set from Damascus Productions is a good resource.  In one of them Jim Phillips gives a good demonstration of a chambered wooden board construction.



I  appreciate your help, and that board looks a lot like my plan. Glassing the board with epoxy would mean spreading epoxy all over the board like a varnish, or would that involve fiber glass? 


You'll probably want to do at least two or three coats of epoxy sanding between coats.

Fiberglass on a wooden board is optional, in my opinion, especially on a chambered board.

The board should have plenty of strength on its own unless you make the deck and bottom walls of the chambers extremely thin.

If you are careful with your glue up you shouldn't have to worry about the board being water tight except for the porousity of the wood.

A few coats of epoxy resin will cure that.

With respect to attaching the fin, you have a few options.

I like "glass on" fins for a wood board as opposed to a fin box but that's just personal preference.

Depending on the construction of the fin you can either attach it with or without fiberglass.

Since you still have time to plan ahead, you can leave the area where the fin will attach solid, or at least thick enough to cut a groove deep enough to set the fin in. I usually try to go about half an inch deep or deeper if I can but I've done less also.

If you do that then you can attach the fin with some thickened epoxy and not use any fiberglass at all on the fin attachment.

That is of course if the fin is strong enough on its own. Like if you're using a fiberglass fin.

You can thicken the epoxy with microballoons or just use some saw dust.

If you're using a thin wooden fin then you probably want to either fiberglass the fin before you attach it or when you atach it.

I usually fiberglass when I attach.

Here's an example of a board where I attached wooden fins using fiberglass to an otherwise un-fiberglassed wooden board:

 All that said, the advantages of using fiberglass on the whole board are:

Extra water tightness

Extra strength

Extra durability.

Down sides could be argued as added weight, added cost and perhaps reduced flexability

Thankyou very much for your helpful input! I’m all ready to go now, SO STOKED!!!

I suggested glassing on the fin, but that isn’t what I did with this board.  I made a slot with a router as shown below.  It actually turned out really nice, but it was a lot of work.

The main reason why I slotted in my fin like I did was because I didn’t want to use fiberglass – just like sqalyboy.  I finished my board with five or six coats of marine spar varnish.  Vanish gives you the clearest glossiest coat imaginable.

I don’t suggest doing what I did, though.  It was a serious pain in the ass, and I didn’t know any better at the time.  I have finished two wooden boards since this board, and used epoxy and fiberglass on both of them.  On the other hand, neither of them came out as glossy as this one. :slight_smile:

One other thing…  Don’t even think about chambering a 5’ 8" board unless you use balsa wood.  It will be too heavy with anything else.

Where are you located?

howdy swied,

great finish you got there, did you apply varnish with a bristle brush, or via compressor (airbrushed)?

also, does varnish require sanding between coats? if so, what grit works best?



howdy swied,

great finish you got there, did you apply varnish with a bristle brush, or via compressor (airbrushed)?

also, does varnish require sanding between coats? if so, what grit works best?



I used a foam brush.  You want to apply lots of thin coats of varnish.  Yes, you need to lightly sand in between coats.  Keep in mind that varnish does not fill in gaps.  If your surface is bumpy, and you varnish over it, then you will still see bumps.

Note:  I don't recommend varnishing surfboards anymore.  Do a search and check out some of the Timberflex boards that resinhead has posted.  He uses epoxy, and then sprays on a product called U-Pol.  His boards are beautiful, and he doesn't have spend two weeks doing the varnish-sand-varnish drill.

I used marine spar varnish on one of my boards, applied with a bristle brush.

I first did several coats of epoxy sanding between each coat.

The final finish was one coat of marine spar varnish.

The finish was OUTSTANDING but I will never do it again.

The fumes were so strong I had to evacuate my work area for days and it was weeks before the smell went away.


Regarding the slot to install the fin, what I usually do is hold the fin against the board where I intend to mount it and then trace around the base with a pencil.

I then freehand cut inside the lines using my dremmel tool and a round cutting bit like this one:

Round Non-Ferrous Cutter Bit (

It takes a steady hand and some patience.

Once I have the slot cut out and I'm happy with the way the fin sits in it, I'll mix up some epoxy thickened with sawdust, trowle it into the slot, then press the fin in place. Clean up the excess that oozes out with a paper towel and then hold the fin in place with a few strips of masking tape until the epoxy cures.

When its all cured I sand down the excess and either fiberglass over it as indicated in my previous post or just paint on a coat of clear epoxy.


Well that's 100 points and no balloon drop.

Guess its time to update my signature.

So making a 5’10 board and chambering it would be pointless unless i used balsa? This is a problem then…

I strongly disagree.

Your board will be heavy.

It will be heavier than any foam board you have ever seen.

But, it will not be a waste of time.

I have personaly made and surfed some very heavy boards and I love them.

Its a different kind of ride than an ultra light foamy but it can be very satisfying.

Here is a link to a ten foot chambered board that is not made from balsa.

My board was mostly balsa with a few strips of redwood.  It weighed about 28 pounds after shaping, but before chambering.  The volume of the board is around 50 liters or 1.77 cubic feet (from AKU).  That makes it an average density of 15.8 pounds per cubic foot.  The finished board now weighs about 16 pounds.  So... 1-16/28=43%, which is the percent weight reduction acheived by chambering the board.  If you get really aggresive you can maybe get up to 50% on a short board like this.  Balsa is much lighter than any other wood around.  I think that Paulonia is around 24 pounds per cubic foot.  If I had made the same board out of Paulonia, then the pre chambered weight would have been 24*1.77 = 42.48 pounds.  If you take out 43% of the material, then you will be left with a 24.2 pound board.  If you are able to reduce the weight by 50% then it will be 21.2 pounds.  That's pretty darn heavy for a short board.  Going really heavy on a long board is okay, but you're talking about building a 5'8".  It's going to be a nugget in more ways than one.  More like a gold nugget.

If you don't want to or can't get balsa wood, then you should probably look into a HWS design or maybe a Timberflex. 

heya swied, thanks for the heads up!


How am i supposed to make a board out of timberflex? I searched it and I don’t see how that would work

I'm not familiar with the Timberflex method of surfboard building but I think it involves laying a wood veneer over a foam core. Similar but somehow different to what would also be called a compsand (short for "composite sandwitch" I think).

If you use the search feature of this forum you should be able to find more details.


check it out surfingsgr8

first 4 threads are must reads

So i’ve done some thinking, maybe skip out on the short stub idea and go 9’0x22 and slap a D fin on it… use it on small days? I can’t get balsa so probably douglas fir?


Try cedar.  Hollow wood construction is pretty cool.

If you start here and go forward, that is my cedar bonzer - if you go backward that is my pin tail.