Wooden board cracking when glassed

I’m currently making a cedar hollow wooden board but the workshop that I build in is VERY cold over winter. I am glassing the board in a separate room with a heater to allow the epoxy to cure, however the top skin of the board has started to split at the end. Is there a way to avoid the cracking? Is there an optimum temp for glassing?

Can you post some pictures?

To be clear;  The wood is splitting or the glass job is splitting??   Also is this a skin of minimum thickness?  Or thicker wood?  Pics?  You’re working with wood.  It’s somewhat “alive” .  It contracts and expands long after that tree is cut down and comes out of the sawmill.  Such are the variables of working with wood.

Does the board have a vent plug?


Another newb w/o enough points to jump back into the discussion…

Shame about the points making it impossible for new users to reply to their own threads, but hey, I have not seen Asian Spam for a few months now…


I have not had issues with cedar splitting during the glassing process, only after, from impact.


Don’t know which method of frame you use, but often on the deck in the nose there will be a strong pulling force from the bottom planks pulling  the stringer rocker down and the top planks pushing it down. This often induces an unintended concave on the hull in the nose, as well as changes the intended nose rocker.  Many HWS have an abrupt bend in the nose rocker because of this, that makes them look all wonky and does nothing for performance either.


Lamming with epoxy, one need not/should  use much pressure on the squeegee as it often forms micro bubbles which turn the epoxy cloudy which becomes exceedingly apparent on top of darker wood.  Did the cedar split when you were using the squeegee, or after, once it started to heat up and thicken?


There are so many little details in making HWS, and climate control is a considerable issue on almost each and every step and often uncontrollable, forcing one to watch the weather closely not only for swell, but times of optimum temperature and humidity for any given stage.  

In general with hollow wood builds, you do not want to rely on the fiberglass for structure, but more for waterproofing of the wood.  Most of the strength should be in the structure and wood, and when the hull panels are pulling down and the deck panels are pushing down, and the rails perhaps doing both, or one or the other, depending on which method you are using, there are all sorts of additional stresses on the wood.

My later builds I glassed the hull wood panel on the inside before attaching it to the frame, and also do the interior of the deck panel too, but this can lead to secondary bonding issues that one must negate the possibility of via mechanical tooth, but without sacrificing the strength of the cloth, or at least minimizing that possibility.

Always try to have warmed wood before applying epoxy, so that the warming epoxy does not heat the wood and blow bubbles, and you really want the epoxy to stay above its minimum cure temp that whole time.  Getting back above temp the next day works, but… the epoxy does not seem to attain the same properties as it should.

If the epoxy says minimum working temperature is 60f, you really do not want it to stay at just above 60f for 4 hours, then fall below it for 12 hours, then put it in the sun the next day until it is no longer tacky.  Really take all precautions  feasible, against this occurrence.

Keep it well above the epoxy’s minimum temperature, and do not use point source heating  in close proximity, which will heat one part of the board more than the other.  Make an insulative box for preheating it if you have to, as it is so much work to get to the point of glassing, that it makes no sense to start half assing it at that point.


   On areas of critical bonding strength, I like to use the green concrete 3m tape on the wood, and push it down tight to the specific area with the back of a fingernail, then rip it off in one direction with the grain, then perhaps again in the other direction with the grain if it did not lift off a bunch of the soft wood inbetween the grains One direction will prove superior, but can change, depending on the wood grain. Across the grain works too, if it is on the interior of the board, but across the grain will show up as stripes on the exterior.

Also beware that this method on some parts of the wood can lift out way too much of the soft wood between the harder grains, not a big deal on the interior, just adds more weight in epoxy than desired, but exterior will be obvious forever after.

  The deeper the epoxy can saturate into the wood fibers , the much better the bond. Sanding dust can be pushed into the grains and impede saturation. 

It depends on the specific piece of wood, but this ‘rip tape’ technique can also add/ or detract to the beauty of the wood too. It can add shittons of effort to the exterior pre lam process, if one starts to do this and wants to blend that look across the whole of the board. 

  If it leaves visible tape adhesive behind when ripping the tape, use less pressure of a back of a fingernail, or skip the fingernail,  or go back to the blue painters tape. Experiment with offcuts first.

Do not use the painters tape stuff with ‘edge block’ for this process and perhaps all processes regarding use with epoxy.  Not sure about polyester resin, as I dont work with that anymore.


If you are trying top repair the split, try propping up the rails in the nose then pushing on the center. Does the crack get smaller?  If so Then you will have to figure out a way to weiught it and lay strips of cloth across the split around whatever you use to weight or put pressure on it in such a way to lift the rails in the nose while pushing down on the stringer, and hold it while the epoxy cures.  It will always want to split forever after, but it will not be in the same spot, likely the opposite side or right next to original split.  Try using thicker roving rail to rail instead of cloth, as no more strength is needed nose to tail, but from rail to rail to prevent the splitting.


I’ve had my longboard’s nose split twice in the last 17 years. The second time included removing a significant portion of the nose panel cutting carefully with a dremel and razor knife, glassing the inside of it, reinforcing the frame, and returning it, to place, then digging grooves into teh cedar rail to rail into which I laid carbon fiber roving, then twice as much glass as originally.

Quite the process but has been good for over 8 years now, and has seen a lot of use before and since.  This particular board was my third and before I started using fiberglass on the interior as well as exterior.