Building Tips

I posted this in another thread, then though it would be a good idea to start a new thread so everyone can add their ideas.

With regard to Razor construction, or Fatbob, or any of my chine designs…I build using balsa. It’s a bit harder to handle than ply, but it’s nice and light, and after building 6 or 8 hulls, I pretty much have it down.

I use 1/32 or 1/6 balsa…sometimes both depending on the stiffness I want. I glue the patterns on the balsa with spray adhesive, then cut out the panels using a scissors.

After removing the plans from the panels (label the parts!) I soak them with 409…a cleaning agent that contains ammonia. Then I prebend the panels and clamp or band them to hold the approximate shape. This isn’t to get the shape exact, just to get a good start on the bend to make assembly easier.

When dry, I tape the panels together on the outside of the hull with lots of masking tape. I’m careful to butt the panels closely…this is where the hull takes shape. Once completely assembled with tape, I put a couple of crossmembers to hold the sheer to the right shape…then I run CA down all the seams from the inside of the hull. Be generous with the CA and it will give the seams good stiffness.

Take the tape off and sand the hull (lightly!!) to clean it up and you are ready for the internal stuff.

It’s a fast and effective approach…I built a new hull in a few hours yesterday afternoon.

Bill H

CA is amazing stuff. In my experience it becomes brittle with age and will fail if it is used exclusively at stress points. My main use for it is to tack parts together that will later be permanently bonded with epoxy. Most new builders use way too much epoxy to glue parts together. My guess is that they are mostly used to using Elmer’s white glue or some other household glue and assume that more is better for a strong joint. That is why a lot you guys have the impression that epoxy is too heavy to use.

In addition, blending micro-balloons into your epoxy mix both weakens the epoxy joint and guarantees that you will use more epoxy than necessary. There is a filler made by West System called “410 MicroLight” which is much lighter and less dense than than micro-balloons. I use MicroLight for fillets around the keel fin joint inside the hull before adding the glass reinforcement strips. If you want to put a fillet between the keel fin and the outside of the hull or between the keel fin and the bulb Microlight is the lightest filler that blends with boatbuilding epoxy. Its purported to be made from expanded epoxy resin (sort of like puffed rice) so it chemically bonds with resin. It is also sort of Balsa colored for you folks who want a “natural” finish to your fillets.

MicroLight can be mixed with epoxy to any consistency thats needed, from runny to stiff like whipped cream. The stiffer the mix the more likely you will have air-bubbles trapped in your application (same is true for micro-balloons). You will find these when you sand the filler back once its dried. In some applications this is okay as any air bubbles can be filled with more Micro-Light/epoxy mix. For a use that requires restricting the flow of your filler, say on a vertical surface (the term is thixotropic) you may want to add a small amount of West System #406 Colloidal Silica or similar product (Cabosil used in pottery glazes). One note of caution though, Colloidal Silica is carcinogenic (like asbestos fibers), Balsa also contains silica, Ca glue fumes can cause lung damage, and I can’t imagine that MicroLight is a benign product either. Boat building should be undertaken in a well ventilated area, away from children or pets and not in your living quarters. Please work sensibly and safely.

That said, MicroLight and Colloidal Silica are widely available through boat building suppliers that carry West System products.

Neil, good call! i think you are right that many folks use too much epoxy in their builds… a tiny bead of the stuff will suffice! the unfortunate part about things like microlight is that they are more expencive than trad. micro balloons… which isn’t helped by the fact that its made by West. however, as you said, if you are trying to save weight, then there is no better way to go than lighter filler, and less epoxy! I am interested in what seems to be a trend of people using hot glue so much to build… that seems to me to be a heavier choice than even poorly applied epoxy, and, it is slightly elastic, so if one is building a boat like Razor, you are losing stiffness. same with CA… there is nothing like a line of resin or epoxy with a little microlight or, if you must, balloons, to add stiffness…

as for the dangers of boat building… everything we use to build boats is a health hazard! i have yet to find a chemical i use that isn’t considered a carcinogen in the state of california! lol. if you are worried about taking years off your life-clock, avoid boat building!

of course, you would then be missing out on one of the best parts of life!

what is the reasoning/benefit to soaking the panels in a ammonia-based cleaner instead of steaming or soaking in hot water? just curious

the ammonia seems to make the balsa even more pliable… and, you can just spray it on:cool:

Another way to make lightweight hard-chined hulls with difficult twists. Go to and buy one sheet of pressure-sensitive white birch veneer and one sheet of plain white birch veneer. Cut parts. Find a convenient form the the desired curve (broomstick, whatever). Bend the pressure sensitive one around, glue side out. Peel paper, apply the other one, use wallpaper roller to press together. Voila! Instant preformed 1/32 birch ply with mylar center and good old waterproof 3M 468 adhesive. Give it a few days to set up, then do corner seams as described above.



I see you are back to experimenting again - eh Earl? :smiley:

Reminds me of the old “Constant Camber” panels for big boats. First layer attached to form, next few layers glued up, final finish layer coated. Remove from hull form, and you have a preformed cambered panel. Only you are doing it with two pieces of very thin veneer. Well done - hadn’t thought of that one !

Hmmm - a preformed, wing mast using this technique perhaps? :wink:

Time to head to the garage to experiment.

After some hot water soaking I got the 1/16 ply to conform to the shape I wanted, and I’m almost done assembling my razor! Only problem now is that I ran out of CA! One problem to the next!

Thoughts on curved panels…

1/32" ply can be pre-curved by working it over the edge of your work bench. Cup your hand over the ply area to be curved and work it back and forth applying pressure as it passes over the edge… take it easy.

If using 1/16" balsa for chine panels how about edge gluing* sheets then cut the panels such that the grain is vertical (across the panel). This has two benefits, curves very easily and avoids ‘cupping’ or hollows particularly towards the bow. I have done this to cover one of my foam cores and I think that is could be worth trying on such as the Razor.

Likewise 1/32" ply can be used with the outer grain vertical without running out of panel strength.


  • Use a wood glue for this, it will sand easily and not cause a hard line as cyano would.

Graham’s point about the hardness of the glue is oh so true and oooooh so often forgotten. Trying to sand anything with major differences in hardness will result in a nice sculpture of a starved dog!


you can say that again angus… :mad::rolleyes:


I set out to built three razor hulls and a son-of-razor, and have fallen at the first hurdle - my cyano wont set!

To assemble depron planes I have used odourless cyano since it came on the market, and use a foam-safe commercail accelerator very, very rarely.

Anyway I have cut out razor panels in depron, 1/16th balsa and acetate projector slide material.

So that I can build “in the air” I painted one edge of the bottom panel with accelerator glued the other and hled while it should harden, but no luck. Either my Zap-O has got weary or something else has prevented it. I will have one more bash then revert to plan B - use PVA woodworking glue and tape to hold it together.

The effect of the accelerator only lasts for a certain length of time. They are all different too. IMO, apply to the cyano to the glueor joint sparingly after you join the panels.

Tomohawk - Thanks for the observation.

I have a sad shortage of hands - only got two and both are used for building in the air.

The accelerator was applied only seconds before the cyano - and was dry before the gluing.

I don’t usually use accelerator - or at least I use BAA*. Cyanos cure by a sufficiency of water, and this makes balsa and depron variable in effect.

So I normally lick one surface - this gives a reliable cure, but can lead to some odd looks if one leaves the house with a boat/plane why stuck to the tongue:)

When time permits I will see if the snag is the cyano or the accelerator (or the builder)

Sorry - Biologically Available Accelerator.

I am reliably told that most body fluids accelerate the cure of cyano but hasten to add that my experimentation has been limited.

Can you post a picture please… :D:D:D

I would, like a shot but both hands were also involved:)

For those seeking a safer & more Earth friendly accelerator for CA glues, you can use plain old ordinary baking soda (make sure it’s baking SODA & not baking POWDER). It’s not quite as fast as a commercially available accelerator such as Zip Kicker, but you could eat the stuff & suffer no real ill effects (unlike eating Zip Kicker). Just apply your CA as usual & sprinkle on some baking soda. A saltshaker makes a good application tool.

Happy Yachting - Kip