Glue for lapstrake

[FrankThomas]

In building lapstrake boats, what is a decent glue to use on the laps? The wood is 1/4 cedar. I am actually building a 1/4 scale model of a Rangeley Lake boat. Someday a full size one but I thought this a good way to develop building skills.

What is the typical glue for freshwater lapstrakes? Epoxy? Brand?

For a non-seagoing model would polyurethane glue like gorilla glue work well?

Thank you

[PAR]

The correct answer is none, with tightly fitted laps on solid cedar planking. Varnish as you please after she's planked up.

[Raggi_Thor]

Generally you will use glue (epoxy, because it seals the wood) if the planks are plywood while you will use clenches (traditional, copper or galvanized) if the planks are solid wood.

[FrankThomas]

Well, my lack of boat building knowledge is certainly showing. With solid wood planks (not plywood) no glue is used at all?? Only the varnish creates the seal? Well the varnish and the craftmanship of builder creating well fitting strakes.

Is there a need for some minor movement between the strakes? Is that the reason for no glue?

Thanks for your input.

[Raggi_Thor]

Yes, and wood has almost no strength transverse to the fibres. A glued joint would be stiff so the wood would easily break. Some builder use a flexible "goo" like sikaflex or similar, but that's normally not necessary.

[PAR]

A traditionally built lapstrake hull (clenched, roved, screwed, nailed or combination of, fastening doesn't matter) using solid cedar planking should have nothing but closely fitted joints on the lap, the moisture gain in the fastened lap provides the seal. Varnish or paint the completed planking, but leave the wood in the laps raw, so they can swell. The only exception to this, would be on scarfs or butt blocks where some will use a sealant (I don't). A well fitting scarf doesn't need sealant, just good fastening. Butt blocks are an amateur way of lengthening planks (in my opinion) and most good builders don't do them on lapped hulls.

There's a great deal of joint movement in solid planked lapstrake hulls. Using epoxy will result in lots of split and broken planks and frames. Other structural adhesives (PU, etc.) will do the same. Sealants such as polysulfide (3M 101 or similar) will provide a flexible bond in the lap, but defeat the self sealing qualities of the solid wood joint. this prevents the moisture gain necessary to tighten the joint closed and firm up the longitudinal stiffening members (the planking) on their frame fasteners.

Plywood planking is a different story, but the original poster was using solid cedar, not ply.

Glued lapstrake is a completely different construction method and relies on different engineering concepts to produce a hull.

These two differing lap methods don't mix well.

[FrankThomas]

Thanks for the very educational response. This beginner thanks you.