Kaholo 14 – Cyanoacrylate vs epoxy "tack weld"?

My last CLC build was an Oxford II shell. Before epoxying and filleting, the hull shape was set using CA glue "tack welds", which I thought worked well, because they set and dried almost instantaneously, and if you wanted to re-set the shape of a thing, you could do it pretty easily.

The instructions for my Kaholo 14 build are calling for a thickened epoxy 1/8" bead tack weld administered from a syringe, which seems like a) an unnecessary complication, b) would add unnecessary weight (albeit minimal) since the whole hull stucture needs to be epoxy filleted anyway, and c) be more un-forgiving in the event that something gets knocked out of whack to allow twist or a panel gap.

Wondering if CLC thinking about tack welds has evolved and my Kaholo instructions are simply an un-updated remnant from when the design was finalized in 2011, or if there's a good reason why I should stick with the instructions and run an epoxy bead along all joints?

My inclination is to use the CA glue to set my hull shape.


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RE: Kaholo 14 – Cyanoacrylate vs epoxy "tack weld"?

Thought #1 - the fillet size will automatically adjust to the presence of the tacking so there's no weight penalty if you apply the tacks and fillets carefully.

Thought #2 - thickened epoxy tacks are mechanically stronger than CA tacks. That strength is not needed on some lightweight boat designs so CA is fine for them. I don't know where the Kaholo fits in terms of strength required from the tacks.

Thought #3 - welding is melting 2 pieces of material with heat so they flow together and solidify into one piece when they cool. Try that with wood and you get charcoal. Tack bonding is my preferred term [/pedantic rant]

FWIW, on my boats I apply the tacks as small smears using a shaped plastic putty knife. This is much less work than syringes and has held together an 18-ft schooner until the stitches were put in.



RE: Kaholo 14 – Cyanoacrylate vs epoxy "tack weld"?

   I've shifted to CA glue for almost all of my tack welding.  Not only does it make the process much quicker, it also helps me gets smoother filets because the tongue depressor (or whatever filet tool you are using) isn't passing over the soon-to-be-submerged "lumps" when smoothing in the filet.  Even if epoxy tack welds are kept small, the discontinuity in sub-suface volume created by the epoxy tack welds can sometimes impact the ease of getting a smooth, one-pass bead of material when laying in a nice filet.  And with epoxy welds you are (or at least I am) almost always guaranteed to create a few lumpy welds that end up higher than the desired filet thickness, and then require attention to sand down prior to the filet.

And for me it really isn't the near instantaneous set up of the glue that does the most to speed things up - it is the fact that you can tack weld a whole boat in just a few minutes.  No time spent mixing epoxy, messing with a frosting bag or syringe, smoothing tools, drips, etc. etc..  Just walk around the boat with a bottle of CA glue with a squirt here or drop there and your'e done. 

I'm currently doing a Rhode Runner and the CA talk welds worked fine.  I did use some epoxy welds at the bow where stresses on the bent planks were quite high and there were some non-contact gaps in the planks.  I didn't want to risk having a CA tack weld "pop" in between removing wires and getting the plank filets done.  I only heard one CA weld pop in the whole process of doing the boat when I leaned too hard on the side putting in the interior longitudinal plank-line mini-filets with a syringe.  I never discovered which one it was, because other than hearing the noise no planks or frames ever moved.

RE: Kaholo 14 – Cyanoacrylate vs epoxy "tack weld"?

   Good thoughts Laszlo. Your experience and expertise are greatly appreciated, as always. And point well-taken on the tack-weld vs -bond verbiage. Although... if we're going to get really pedantic, there is a more general use of the term 'weld' that defines the joining together of any two parts into an harmonious whole, which could well apply to parts of a wooden boat. However, I agree that tack-bonding is probably a more precise term for what we do in S&G boat building.  :)

I think I'll try your epoxy smear technique. Any particular shape for the putty knife that you use?

RE: Kaholo 14 – Cyanoacrylate vs epoxy "tack weld"?

I am also pondering the merits of a thoughtful applicaiton of CA glue for some of the tacking work. As far as I can distill the differences for this specific project:

Pros: Faster set up time leads to less chance of shifting during the process; smaller tacks leads to a smoother filleting process

Cons: Faster set up time leads to less room to maneuver in the event minor fit adjustments are necessary

I am not concerned about overall process time differences or cost difference.

Given the above I think it makes most sense to just use CA for the areas where there's a high risk of movement that I want to prevent while the epoxy cures,  like with panels that tend to shift or in the transom area.

Thoughts? TIA, Steve

RE: Kaholo 14 – Cyanoacrylate vs epoxy "tack weld"?

If the CA bond is good enough to hold a Rhode Runner together as Bubblehead has demonstrated, then it's plenty strong for a Kaholo.

My filleting tools. Left is how it comes from the store, right is after I get done with it. The rounding is meant to be the same as the US 5 cent coin.

I use the rounded tool at an angle to lay down the smears and straight on to lay down the fillet. That guarantees that the fillet is the minimum size needed to fill the joint with a nickel-radiused fillet (which meets the minimum radius requirement for up to 6 oz. glass) as well as ensuring that the smear is covered without a visible trace or void. The straight tool is used to pick up any excess from the sides and lay it down in the next segment of the joint.

Finally, if either the epoxy or CA is being applied while the wires are still in, the wires themselves will hold the pieces in place while whichever tack type cures.

So for the original question, for the Kaholo it pretty much comes down to individual preference.

Have fun all,


RE: Kaholo 14 – Cyanoacrylate vs epoxy "tack weld"?

Just thought i would add my 2 cents here...

i have become a huge fan of the CA Glue (with accelerant spray).  so far, has held some pretty challenging bits with little problem.  used to do this all with epoxy but after making the transition not likely to go back.

fwiw, if you do find you glued up something misaligned, i find it easier to cut a CA glue 'weld' with an exacto knife easier than cutting a bad epoxy 'weld'.   cut a couple of the misaligned welds, realign, and done!




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