[Rokeby]

Re: waterproofing cardboard structures... a non-intuitive method

I've had very good success waterproofing cardboard boats with
contact cement, either the original or new water-based formulas.

Just apply with a roller and let it dry thoroughly. It really soaks
into and grabs onto the cardboard. When dry it remains flexible
which is a good thing as the cardboard has a lot of "give."

It is an excellent substrate for water based paint. Although it
might seem like overkill, I recommend finishing as per: contact
cement-primer-paint to get the best film adhesion. One boat
that I designed for and directed building of for a corporate client
was used for three cosecutive years with no waterproofing/paint
failures. (We used triple corugated refridgerator box cardboard.)

I wish that I had see this thread earlier, there are many little
construction tips that lead to a stronger, longer lived cardboard
structure.

For example, it is very difficult to get a good solid glued joint
where the edge of a piece meets a flat surface. The end of the
corrugation just doesn't provide enough surface area. This can
be overcome by including a folded-over flange on the edge-on
piece.

The additional surface area thus created provides a much
stronger joint in two ways: first, it provides greater area for
the joint between the two pieces. It also spreads out shear and
tension forces in the smooth face ply of the flat surface. This
helps prevent the separation of the face ply and interior
corrugations, which are simple glued joints,easily pulled apart
in tension.

At any rate, it looks like you've done a good job. I look forward
to seeing how your work holds up and what aero benefits it
provides.